How to: Ford Explorer - Ranger TPS Test Procedure

[Pontisteve]

Sounds like you've still got something wrong, but at least its better. I suppose you could try to decrease your throttle stop screw even more. Cars with stock cams can idle at surprisingly low RPMs, like 400. You can drop it as low as possible, even to the point of stalling or inconsistent idle, and as long as your TPS is above .9, it'll probably work. The thing is, I feel we're compensating for some other problem at that point.

By giving the IAC room to move the idle speed up or down, we've basically allowed it to correct for any problems. The thing is, there should be no problems to correct for, ideally. We're dropping the range lower than the factory probably intended, but still within the OEM specs. Fixing your vacuum leak or bad coolant sensor (whatever you find with your new scantool) will ultimately fix things.

Another slim possibility is that you don't have a bad coolant sensor, but have a bad thermostat, holding the truck too cool.

The calibration will have an idle airflow amount built in, and that is the amount of IAC that the truck "starts out" with. The IAC (if properly set to around 30% duty cycle at idle) has the room to raise that speed a lot, or lower that speed a little (30%), but if everything is right with the motor and EFI, it basically shouldn't have to be making these corrections.

With the scan tool, you can look at IAC duty cycle. If the RPM is 1100 and IAC is at 30 or 40%, and the PCM sees the high idle problem and tries to lower idle via the IAC, you'll watch the IAC duty cycle drop in the scan tool until it hits zero. At that point, there's nothing more the PCM can do to drop idle. See now, the relationship between IAC range, duty cycle, and idle speed? Once you figure it out, it seems amazingly simple and common sense.

Get your innova, and check coolant and IAT temps before starting the vehicle, and as the vehicle warms up to full operating temp. Along the way, look at IAC duty cycle. It'll start out higher, as the PCM is commanding that 600 rpm (or close to that anyway) idle speed. If 600 rpm = 30% duty cycle, then to get to a cold start 1200 or 1400 rpm (whatever the calibration calls for), then the duty cycle would have to raise up to maybe 60 or 70% (again with some room to go further if there is any problem!). As the truck warms up, commanded idle speed will slowly reduce, and so will IAC duty cycle, until it bottoms out at the warm idle speed and hopefully that's around 20 - 40% duty cycle.

Can we push our range further up or down? Yeah, but we really shouldn't have to, and it's a clue that were compensating for some other problem. Plus, by making the computer do above average IAC corrections, we're guaranteeing that it will start out at a much higher idle speed and work its way down, instead of just starting out at the correct idle speed.

Welcome to the wonderful world of OBD2. You're gonna love having live data, and you'll realize you were in the Flintstone world until now

 

[drdoom]

Need Help

I need some help here. I have re-done my TPS test a couple of times, and I cannot get the correct readings. Here is what I have:

At HARNESS, reference voltage is 5.0 volts

At BACK-PROBE, throttle closed, 0.24 volts, then a gradual increase to 1.85 volts at WOT.

I have checked it over and over, still the same.

BTW, I don't have any trouble codes, and the only drive-ability issue I have is a harsh 2nd to 1st downshift. I am just checking things out before I go back into the valve body.

 

[2000StreetRod]

TPS out of range

I suspect if the PCM was reading that low a voltage at closed throttle a TPS out of range code would be set. Try measuring the voltage between the wiper and the reference voltage. It should be about 4.0 volts at closed throttle and about 0.5 to 0.2 volts at WOT.

 

[drdoom]

OK Dale. I will try that tomorrow, and let you know. Thank you for responding.

 

[silv86]

high idle problem + rotten egg smell and miss

I have been experiencing the same problems (high idle, decel issues) as described in this thread. My main motivation to do this was for the obviously high idle, previously tampered with throttle stop adjustment, it wasn't even touching the throttle plate. Therefore there wasn't anything stopping it except the butterfly bottoming out in the throttle body.

I have after reading through the thread, tested my TPS resulting in .92 volts @ idle and 4.64 volts @ WOT. Also, while with the DVM hooked up I progressively went from idle to WOT resulting in a smooth gradual increase in voltage without any drops or jumps. TPS seems to be working properly. I then adjusted the throttle stop screw until i noticed an increase in voltage to .94 volts. I did all this with key on engine off position. (After typing this I think I might have done something wrong)

Now after doing all of this I proceeded to clean the throttle body because I have noticed a sticky throttle upon acceleration occasionally. Probably due to the miss adjusted throttle stop screw I assume. Throttle body appeared to be clean aside, so I did a quick clean with a damp paper towel. I did notice there was no factory sticker about not using solvents thought that I thought was odd. After cleaning the TB I rechecked the the TPS sensor readout to see if there was any difference. The idle was the same .94 volts and the WOT was 4.66 volts a little higher...

I then removed and cleaned the nice shiny IAC valve that was dated I am assuming when it was put on about 5 years ago. The inside was pretty clean, went ahead and cleaned it anyway and re installed it and plugged it in. After putting it all back together and firing it up I instantly noticed that the truck was idling rough(missing) @ <1000rpm, which is about normal maybe a little lower than it has been but it fluctuates 900-1200rpm in park lower in gear. Keep in mind it is in the mid 30's today, but the truck was already fairly warm having been driven about an hour or so prior to doing all of this.

I popped to the hood now dark outside used my flashlight to see if there was any obvious problems( unplugged MAF, TPS, IAC valve, etc) to see if I had forgotten something. All seemed as it should. I continued to drive the truck about 2 mile round trip to store and back thinking it might just need to driven a little to readjust or clear up. This miss did not go away although in park if revved above 1000rpm's or so it felt like it went away but cam back when letting of the gas, same when driving. I started to notice sulfur smell in the when driving, I didn't think anything of it until I noticed it following me everywhere i went, then check engine late came on stopped by parts store (P0301) obviously I could ave guessed a miss fire code, was hoping it would be something more detailed. Cleared it and returned home.

After returning home still missing, smelling like rotten eggs, and running normal operating temp, I am stumped... I am going to do some more trouble shooting in morning.

I am wondering and worried that it could be something to do with my cats, but find it coincidental that they would act up directly after the small adjustments I had just made. Also I did notice that there was no difference in idle at all when the IAC valve was unplugged as well as MAF and TPS, in fact it didn't make any noticable difference in idel when these were unplugged, thought that was odd.

Sorry for the lengthy explanation just thought I shouldn't leave anything out. any insight would be great. I plan on doing some more troubleshooting tomorrow, maybe resetting the throttle stop back to where it was and draining the alive memory to see if that makes a difference.


Thanks

 

[silv86]

Update... I got rid of the missfire, somehow I had a loose connection to one of my coil packs causing a missfire in cyl #1... Now that that is fixed I am still experiencing a high idle as before. I think that I have narrowed it down to a bad IAC valve...

I did the reset as stated on losota racing's link. before doing this I set the throttle body stop screw so that my TPS sensor was reading the .92 volts it was reading when I first started before adjusting it to .94. I pulled the plug on the IAC valve to see if the idle dropped in which it didn't... I then inspected the inside of it to see if there was any obvious obstructions to no avail. Also, while it was off I used a pick to see if it was bound up and noticed that there wasn't much movement maybe 3/16" or so(I don't know how much movement is normal but, the movement seemed restricted), I then reinstalled, and just to be on the safe side I started engine back up and covered the throttle body with my hand to see if I could kill it and see if there might be any existing vacuum leaks I have already checked for or if the IAC valve would compensate. The motor did stall out after restricting throttle body inlet with my hand. I then hooked everything back up plugged IAC valve in and started it. Nothing changed although the IAC did respond to unplugging it this time but after shutting the truck off and starting it again the IAC would no longer respond(lower RPM's).

I think I am dealing with a bad IAC valve. Also I don't know if this makes a difference but when I measured the volts to the TPS sensor I got 5.10 volts, is that acceptable? I know it mentioned 5.00 volts was normal in this post I believe.

 

[silv86]

Replaced my IAC with motorcraft IAC and it didnt seem to change a thing... Before I changed my IAC, The idle was unaffected by unplugging the IAC, it is my understanding that the motor should die or almost die when the IAC is unplugged. I am wondering if there is something wrong with my computer... My wiring engine compartment looks near new with no melted, frayed or cut wires... I have checked for vacuum leaks more than once with starting fluid to see if there is a change idle to no avail. Just looking for some suggestions, maybe fuel related, or temp sensor... My truck did have a coolant leak, but never affected to temperature at least from the gauges stand point. Any suggestions would be great.

thanks in advance.

 

[Pontisteve]

With the engine fully warmed up, unplugging the IAC should drop engine RPM. One reason why it does not might be that you have the throttle body stop screw adjusted too far open. The engine itself without the IAC should be idling very low, like 500 RPM or something. Barely able to run, maybe even stalling. The IAC brings that up from minimum airflow up to the airflow required to idle the car.

With this design, it gives the IAC complete control of the idle speed, up or down. If the throttle body stop screw is set so high that it idles at 800 RPM without any IAC help, then the engine would never be able to be slowed down below that.

I would start with checking TPS voltage. Then, open the throttle body by hand and slowly close it while watching the TPS voltage. See if it consistently returns back to the same .94 volts or whatever your TPS idle voltage is. Make sure the throttle body is clean, and not carboned up, as that can prevent it from closing all the way.

The TPS has 3 modes... idle, part throttle, and WOT. Idle is whatever the PCM sees when the key is first switched on, perhaps .94v. Should be set between .94 and .99v. Part throttle is anything about .03 or .04 volts above idle. And full throttle is usually something like 3.68 volts and up, or 3/4 throttle.

If your TPS tells the computer you're in part throttle mode, it will open the IAC up some. If you're really at idle, not part throttle, this can cause issues. So the TPS must always return back to idle correctly. This means a clean throttle plate, no binding, no throttle cable issues (rare), and a correctly adjusted minimum airflow screw.

The only other sensor that has much effect on idle speed (other than the MAF, which dramatically affects air/fuel ratio) is the coolant temp sensor. The PCM reads the engine temp, and raises idle speed up, the colder the motor is.

 

[silv86]

I get .92volts at idle and 4.64 at WOT, with a smooth transition between the two numbers. I will recheck everything and go from there, thanks for the info.

 

[silv86]

I can't believe it... I took my truck to a mechanic shop to run the scan tool on my truck only because they were cheaper than the dealership... They ran the diagnostics test and the truck passed with flying colors. The mechanic then while the truck was running, opened the oil fill plug, only to hear a loud vacuum noise... They pulled one of the pcv valve hoses loose from the back of the intake to check the pcv valve, and told me that it seemed like too much vacuum to be a bad pcv valve, told me that it was the intake gaskets... I thought this was an unusual diagnosis because it doesn't use oil or coolant... Told me it was a 6hr job and that they could do it. They must mistake me for a sucker... They did however find my problem, but thought I was a complete idiot and try to sell me a intake and valve cover gasket replacement job...

30 minutes and $51 later feeling a little "sore in the rear" I was on my way to purchase a pcv valve, Bought a replacement pcv valve from autozone $4(dealer didn't stock it, and I had to order a complete assembly of hoses and pcv valve all in one) popped it in my truck and bam, idles at about 5-600 rpm.

I guess I could consider myself an idiot for not having checked the pcv valve in the first place! It is rather hard to replace having not replaced one on a 5.0 being the second ford product I have owned(1st lincoln navigator/completely different), also my hands look like I got in a fight with a brick wall. I have ordered the factory pcv valve assembly $37 which I was told comes with all three rubber hoses, very easily broken double ninety degree plastic union, and the pcv valve itself.

Well hopefully someone will learn from my mistakes and self them selves some time and money

 

[Pontisteve]

A smoke machine would have told the story on that one!

Generally, there isn't much to a PCV valve. It's a hollow tube with a check ball in it. If you shake it and the ball moves up and down each time, it's probably good.

 

[LoadedLimited]

Tps smoothly increases than goes open line

Hmm,
I tested my tps and at idle it reads 1.03, a little high but OK. I the roll on the throttle and the voltage slowly increases till it gets to about 2 volts. Right at this point I continue towards WOT and the sensor goes to reading OL "open line". I just changed out the tps and same thing happened. I used the method of measurement laid out in this thread. Thoughts?

Thanks in advance for any input.

 

[LoadedLimited]

Lol. Took me 30 minutes to figure out that the multimeter was on the 2v max setting. All is well, sorry for the false alarm.

 

[Jstcruz]

Im sorry if it has already been covered but, what should the TPS readout on a Scan Gauge be? Mine is showing 19.

 

[2000StreetRod]

Absolute throttle position

Im sorry if it has already been covered but, what should the TPS readout on a Scan Gauge be? Mine is showing 19.

19% was the reading I got for closed throttle when using my Windows based Dyno-Scan program. WOT was 92%.

 

[Jstcruz]

19% was the reading I got for closed throttle when using my Windows based Dyno-Scan program. WOT was 92%.

Good to know, thanks! I thaught something was messed up! Thinking it should of been at 0 or 1-2 :/

 

[Pontisteve]

The reading you are seeing in the scan tool is a generic function. Different scan tools will show different readings, depending on how they scale the data. Scan tools read the voltage, and then calculate a percentage. Most sensors, including the TPS sensor are 0 - 5 volt analog signals, so the % you see is based on 5 volts.

So 19% = .95v, and 92% = 4.6v in the example above.

Looking at raw voltage would be a much better way to read the TPS sensor, but % can be handy for doing the sweep test.

Typical values for a Ford are .98v at idle, and 4.65v at WOT.

An acceptable range might be .94 - 1.02v at idle, and 4.6 - 4.7 volts at WOT.

The TPS sensor sends a raw analog voltage signal to the computer, based on throttle position. The more throttle, the more voltage. The computer takes this voltage and breaks it down into three categories. CT (closed throttle/idle), PT (part throttle), and WOT (wide open throttle). The computer learns what CT and PT are.

When you first hit the key, the computer knows the truck is at closed throttle while starting, so it learns whatever voltage you're at right then, and calls that CT voltage. Along the way, the computer constantly monitors this closed position, and occasionally may update what CT really is. So if you hit the key, and the current TPS voltage is .98, then .98 becomes what the computer thinks CT is unless it learns otherwise later.

PT is determined by normally being .04 volts higher than CT. In other words, if you move the throttle .04 volts more than what idle is, the computer determines you are now in PT mode.

WOT is determined based on the computer calibration, but is generally speaking about 2.7 volts higher than idle. So if Idle is 1.0 volts, WOT would probably be 3.7 volts or higher.

The "mode" that the car is in determines the strategy the computer uses. For idle, it allows closed loop spark fluctuations to perfect idle quality. It is also used to trigger the dashpot function in the tune, for controlled deceleration rates (via airflow thru the IAC).

In PT mode, the car quits playing games with the timing, and runs a much more fixed timing value, based on calibratable tables in the PCM tune. At WOT, the car switches over to open loop mode (after a small waiting period - the time of which is calibratable in the tune), and runs a different set of timing values and air/fuel ratios.

In reality, the computer uses an A/D converter to convert the 0 - 5 volt signal into a 0 - 1023 AD count. Each volt = 204.6 AD counts. The computer tables are all in AD counts in the tune. And all the tables in the PCM are based on RELATIVE throttle position. That's relative to closed throttle. In other words, WOT = 555 counts relative to CT. So if CT = 1volt (205 AD counts), then WOT would equal 760 AD counts. And that calculates out to 3.71 volts if idle is 1v.

GM vehicles will often have the factory computer scale throttle percentage for you. So the GM computer will learn that idle is (in a GM) around .6 volts, and WOT is maybe 4.5 volts. The computer will then scale 0 - 100% to be equal to .6 to 4.5 volts. So when you datalog a GM computer, the throttle position percentage will make a lot of sense (0 - 100% is easy).

Ford computers don't really do that. They just convert the voltage to AD counts, and use relative AD counts in the tune to figure up everything. Any % being shown on a scan tool is just to make a mechanics life easy. But most good mechanics just look at voltage.

TPS sensors have 5v going into them, and spit out between 0 and 5 volts coming out, depending on the resistance in the sensor. This resistance changes because of a film inside that's thicker on one end and thinner on the other. This film can wear out over time, especially between idle and about 2 volts (where your foot is most of the time).

To properly test a TPS sensor, datalog it (or backprobe it with a voltmeter), and slowly rotate the throttle position from idle to WOT, while watching the TPS voltage. It should slowly and steadily rise linearly, always going up at a nice, consistent rate. If you see any skipping around of the voltage, or voltage drop outs (sudden reduced voltage spots), the TPS is bad. Replace with a factory Ford one and done.

 

[mesaroad]

high idle/over-revving between shifts

I'm new to the forum but have been following the TPS discussion. Along with many others, I am experiencing high idle/over-revving problems with my 2003 Ranger 4.0. FX4 manual. Mine occur between shifts (+ 200-300 rpm's), while coasting in neutral (1100-1500 rpm's until arriving at a full stop then it will drop back to 750), and starting a fully warmed engine (jumps to 1200-1300 rpm's and stays there until gear progression or an eventual stop causes a change.

I have cleaned the MAF sensor and the throttle body, changed the PCV valve and checked for vacuum leaks, cleaned the IAC valve and gone through the idle adjustment procedure, setting it at 750 rpm's (550 with IAC disconnected). At this setting the TPS reads .91 at idle, 4.64 at WOT with an even progression in between, and 5.02 volts to the PCM. When I set the TPS at .98 by adjusting the throttle plate, the idle goes to 850 rpm's and the other high revving problems become more accentuated.

Any suggestions about where to go from here? The TPS appears to be working though the idle voltage is low and the IAC plunger is clean and free to move. Does the fact that the idle eventually settles to 750 eliminate the possibility of valve cover or intake manifold gasket leaks?

The truck only has 50,000 miles on it, though it is new to me. I have never experienced this high revving behavior in any other vehicle.

 

[Pontisteve]

What you're describing is too much airflow at idle. Total idle airflow is made up of two things: air passing by the throttle plate, which is a function of the idle stop screw setting, and air passing thru the IAC. Think of the IAC as a miniature throttle body that is computer controlled.

The air going past the throttle plate should be just barely enough airflow for the engine to idle on minimally. In other words, if there was no IAC (or it was unplugged), the airflow going past the throttle plate should just barely run the engine. On a factory engine, that means maybe 400 - 500 RPMs worth.

Once the engine is able to just barely even idle, the IAC's job is to bring total idle airflow up from the base airflow setting (air passing the throttle plate) to the desired airflow setting (a setting in the computer calibration). The desired idle airflow is based on a calibrated table in the PCM that is RPM based.

This way, the computer can add more airflow when the coolant temps dictate a higher (cold start) RPM. For example, 0 degrees outside might require a 1500 RPM idle speed, but as the engine warms up to 50 degrees, it might want 1200 RPM, 90 degrees 1000 RPM, and anything over 140 degrees maybe 700 RPM. I'm making these numbers up, of course.

If you have too much throttle body stop screw setting, the computer still adds in the same amount of idle airflow thru the IAC, and the total idle airflow becomes too much because the base setting was too much.

First, to check the IAC, let the engine idle and then unplug it. (This will probably set a code). If engine RPM suddenly drops, or the engine stalls, then the IAC was doing something. Or if you start the truck in the morning, and it has a high idle that slowly lowers as engine temps warm, then the IAC is working. Cleaning it won't hurt a thing.

Next, if you have never adjusted your throttle stop screw, then don't. It shouldn't need adjusting!! If you've monkeyed with it, then it may need to be reset. For this, I would try unplugging the IAC, and then slowly turning the stop screw out until the engine just barely will run, or maybe just starts to stall. Then plug the IAC back in, and you should be good.

An alternate method is to turn the throttle stop screw out until you have .010" of gap between the stop screw and the throttle body lever. Then turn the screw in one full turn.

But if you have a stock engine, have never tampered with the idle screw, and are having trouble with high idle (after cleaning the IAC), then you probably have one of two things going on. Either your throttle body needs cleaning, and carbon is preventing the throttle plate from closing (which should basically show up as a higher than normal TPS reading at idle), OR you've got a vacuum leak.

Vacuum leaks could be a variety of things. Blown intake gaskets, rotten vacuum lines, cracked plastic vacuum lines, bad brake booster diaphragm, or even a bad o-ring on your dipstick tube.

The PCV & dipstick tube all need to be sealed up. The PCV system basically sucks fumes out of the oil pan and internal engine spaces, and ultimately that air gets burned in the combustion chamber. Therefore, we need to add fuel for that air. That fuel is added by measuring the air going into the engine with a mass air meter. So ANY AIR not going thru the MAF, and yet getting burned in the combustion chamber, is an unmetered air leak, and creates a lean condition that can cause a high idle.

Here's an example of this. A stock 5.0 mustang GT where the guy removes the PCV hose that goes from the passenger valve cover up to the throttle body, and replaces this PCV hose with a little K&N valve cover filter. By doing this, he's allowing unmetered air INTO the engine crankcase, and that air ultimately gets in the PCV valve, intake, and combustion chamber. This air isn't metered, so it isn't fueled for. So the motor runs lean at idle, and lean engines tend to rev up some.

You should also check your intake tubing, between the mass air meter and the throttle body, to see if any of the joints are loose, the rubber is cracked, or any hose grommets are cracked/missing. All intake tubing must be leak free.

If you've exhausted all of this, and your brake booster holds a vacuum, and your charcoal can vacuum line (and all others) aren't rotten and porous, and are properly routed, then I would suspect intake gasket leaks. Remember, they may not be an external vacuum leak. They may leak from the bottom side of the intake ports.

Cold engines have gaskets that leak more air than when warm. So if you have a scan tool, datalog your long term fuel trims and watch to see if they are huge when cold, but shrink when the engine warms up. For example, going from a 1.15 LTFT cold to a .98 to 1.06 when warm tells me that the engine has to add more fuel when cold and idling, then when warm and idling. This could indicate an intake gasket leak. Other types of vacuum leaks would probably just always leak the same, causing large LTFT's at idle all the time.

 

[Jstcruz]

I greatly appreciate all the input on this thread. Thank you guys!