TPS reading .89 volts-4.59 volts

[jcwaters1]

TPS reading .89 volts closed-4.59 volts wide open. is this a normal range? my reason for checking it is when i rev the engine up to about 1000 RPMs, say when reversing an unloaded trailer, and snap the throttle shut, the engine slows to almost 300 rpms and shakes and then comes back up to about 500. is this normal? or what else should i check?

 

[manaen]

you can start by setting your closed tps to .95v that will greatly help throttle response. The tps does not have as much of an impact on idle speed as the IAC (Idle Air Control) valve does. You need to clean/replace the IAC. Also you will want to check for vacum leaks. In some cases the throttle body idle set screw can move/wear and the iac is not within its correctable range.

If memory serves correct you can set the throttle stop screw by unplugging the IAC set the idle around 450 to 500 then plug the IAC back in. The idle should raise to 750. If the idle. BEFORE YOU DO THIS make sure you check for other problems. Idle will be effected by many other factors you need to rule those out before adjusting the manual stop screw. However in my case one time when I unplugged the IAC the engine stalled and I knew that there were no other problems. After re-adjustment my engine idle was much more stable.


So I would check
1) plugs/wires
2) clean MAF
3) check/replace air filter
4) check for vacuum leaks
5) check fuel pressure (it's always a good test to do)
6) clean/replace IAC (you can try cleaning first but many time they just go bad)
7) if all else fails check your throttle stop position

Good luck

 

[2000StreetRod]

TPS voltage & idle speed

Did you read the voltage to ground or the sensor return line? See my TPS Test Procedure for more info. There's a link to it in My Helpful Threads in my signature.

You may want to perform my Idle Adjustment Procedure.

 

[jcwaters1]

you can start by setting your closed tps to .95v that will greatly help throttle response. The tps does not have as much of an impact on idle speed as the IAC (Idle Air Control) valve does. You need to clean/replace the IAC. Also you will want to check for vacum leaks.

1) how do i set the voltage to .95 volts?

2) i have cleanes the MAF and IAC today... no change

3) how do i check for vacuum leaks EXACTLY? i have never been told exactly how to do it..


thanks guys

 

[jcwaters1]

Did you read the voltage to ground or the sensor return line? See my TPS Test Procedure for more info. There's a link to it in My Helpful Threads in my signature.

sensor return line.

 

[Carguy3J]

The TPS is NOT adjustable on the 4.0L SOHC. If I recall correctly, anything under 1v, at idle is fine. As for the 4.59v, at WOT; that's a little low. I would check and see if you are actually getting full throttle. (ie, the throttle blade is open all the way when the pedal is to fully presses to the floor) The 2nd gens are know for 1.) the throttl cable stretching and 2.) the weak little spot welds holding the gas pedal assmbly to the firewall breaking. Either condition will prevent you from getting full throttle. do a search on the forum for "throttle cable mod" and "throttle pedal", you should get all the info you need on fixing those issues.
As for the stalling/low idle:
1.) Why are "snapping" the throttle shut when backing up a trailer? Practice better throttle modulations skills.

2.) Suddenly closing the throttle with the engine under load could possibly cause a brief "undershoot" like you describe, with nothing wrong. This situation could be further exasperated if you have the a/c (or defroster) on, as this places a further load on the engine. Does it idle normally? Does it do this under "normal" driving conditions? If not, then I would say that it is more related to how you are operating the vehicle then anything being wrong.

3.) are the symptoms the same regardless of engine temp and/or ambient temp? IF not, then you could have an ECT or IAT sensor going bad?

4.) Yes, as others have suggested, it could very well be your IAC valve. I have never had a "bad" one start working after any reasonable amount of cleaning. If it's bad, replace it. Another possibily is a sticking egr valve. You can test the proper function of the egr valve with a hand vacum pump. Advance and/or Autozone should rent the, or buy one for about $20-$30. It's a very useful tool to have.

5.) I see in your "sig" you say you have a "chip". What, exactly, do you have? Depending on just what your "chip" is, it could be related.

 

[jcwaters1]

The TPS is adjustable on the 4.0L SOHC. If I recall correctly, anything under 1v, at idle is fine. As for the 4.59v, at WOT; that's a little low. I would check and see if you are actually getting full throttle. (ie, the throttle blade is open all the way when the pedal is to fully presses to the floor) The 2nd gens are know for 1.) the throttl cable stretching and 2.) the weak little spot welds holding the gas pedal assmbly to the firewall breaking. Either condition will prevent you from getting full throttle. do a search on the forum for "throttle cable mod" and "throttle pedal", you should get all the info you need on fixing those issues.
As for the stalling/low idle:
1.) Why are "snapping" the throttle shut when backing up a trailer? Practice better throttle modulations skills.

2.) Suddenly closing the throttle with the engine under load could possibly cause a brief "undershoot" like you describe, with nothing wrong. This situation could be further exasperated if you have the a/c (or defroster) on, as this places a further load on the engine. Does it idle normally? Does it do this under "normal" driving conditions? If not, then I would say that it is more related to how you are operating the vehicle then anything being wrong.

3.) are the symptoms the same regardless of engine temp and/or ambient temp? IF not, then you could have an ECT or IAT sensor going bad?

4.) Yes, as others have suggested, it could very well be your IAC valve. I have never had a "bad" one start working after any reasonable amount of cleaning. If it's bad, replace it. Another possibily is a sticking egr valve. You can test the proper function of the egr valve with a hand vacum pump. Advance and/or Autozone should rent the, or buy one for about $20-$30. It's a very useful tool to have.

5.) I see in your "sig" you say you have a "chip". What, exactly, do you have? Depending on just what your "chip" is, it could be related.

1) the engine has done this forever. even before the chip.

2) how would i know if the iac was bad if i didnt clean it first? how can i tell it its bad?

3) symptoms the same as long as the engine is at operating temp.

4) i have been backing up trailers for a long time, and i know how to drive. every other truck i have driven hasnt done this. it doesnt seem like it should almost stall everytime i close the throttle. if you are going slow, at 1000 rpms, and need to stop, you arent going to slowly let off the 1/8 of an inch that the throttle is pushed down. are you?

5) also, when i took the volage readings, i was at the throttle body, hand moving the plate, i wasnt pressing the gas pedal.

 

[jcwaters1]

it also does it when its not under load...just sitting there in park it will drop below 400 rpms if you close it after being @1000 rpms

 

[Carguy3J]

1) the engine has done this forever. even before the chip.

Ok, then it's probably not related. Still curious what this "chip" is.

2) how would i know if the iac was bad if i didnt clean it first? how can i tell it its bad?

Does the engine idle ok? Does it "stumble" as you described if you do a quick throttle snap test in park/neutral? If it idles poorly (very low and/or "hunts" up and down) and/or has a hard time recovering from a quick snap test w/ no load, then I would suspect the IAC. If the idle is "hunting", unplug the IAC w/ the motor runnning. If the idle smooths out, it's the IAC. If it idles low, and you can hold a smooth steady idle by opening the throttle a little, then there is a good chance the IAC is bad.

3) symptoms the same as long as the engine is at operating temp.

So it doesn't show any symptoms when the engine is BELOW operating temps? If so, check the accuracy of the ECT (coolant temp sensor). Start form an overnight cold-soak. Use a quality liquid thermometer (or an infrared thermometer) to measure the actual coolant temp. You'll also need a scan tool hooked up to the OBD2 port at the same. Continue to monitor and compare the ecm reported temp to the actual measured temp throughout the warmup cycle. If there is more then a few degrees difference, then replace the ECT sensor (make sure it's the one for the ecm, not the dash gauge)

4) i have been backing up trailers for a long time, and i know how to drive. every other truck i have driven hasnt done this. it doesnt seem like it should almost stall everytime i close the throttle. if you are going slow, at 1000 rpms, and need to stop, you arent going to slowly let off the 1/8 of an inch that the throttle is pushed down. are you?

Well, when you put it that way, I guess not. On the other hand, I wouldn't have referred to that as "snapping the throttle closed". No, of course it shouldn't stall under that condition. You didn't really answer my question though. Does it only show these symptoms under these specific conditions? (with a trailer / other heavy load), or does it do it all the time, such as stopping at a traffic light, when not towing anything?

5) also, when i took the volage readings, i was at the throttle body, hand moving the plate, i wasnt pressing the gas pedal.

If you are sure you were opening it up to full throttle (if you have a tight return spring, it's possible that it felt like it was open all the way, but maybe you didn't get it open that last little bit.), then you might also want to test the TPS further. Fist of all, make sure the throttle shaft is in good shape. If it has any "play" in it, that can cause intermittent vacum leaks, and cause erratic TPS readings. If the shaft is "sloppy" then you would need to replace the throttle body. If the shaft seems ok, hook up your voltmeter again, or even better, use a scan tool to monitor the TPS voltage right from the ecm. Watch the voltage as you work the throttle open and closed (best to do it with the engine off, so you can get the widest range of reading without overrevving the engine) Make sure that the volltage changes smoothly and linearly with the movement of the throttle. There should be no erratic jumps in TPS voltage, or "dead" spots. "snap" the throttle a few times. (open it to various positions, then shut abruptly) Make sure the sensor quickly returns to a closed throttle voltage. Also look to make sure that that closed throttle voltage stays the same throughout the test. A variation of a few hundreths of a volt is ok. More then that, and something is wrong: a.) a bad sensor, b.) sensor mounting screws loose (unlikely, as they have loctite on them), c.) "play" in the throttle shaft, d.) a worn throttle return spring causing inconsistent throttle "return" action. Every time the throttle is closed, then ecm looks for and learns the lowest TPS voltage that it sees, and records this as "closed" throttle. If that voltage is constantly jumping around, that could mess with the idle control strategy.

6) one last thing. you said that its possible to adjust the tps, how exactly do you do this?

Sorry. That was a typo. I have since edited my previous post. It is NOT possible to adjust the TPS on a 2nd gen w/ a SOHC. Yes, some guys have tried "slotting" or oblonging the mounting holes in the sensor. However, there is not much "meat" there to do that, and really, if the sensor is out of range, it should be replaced.

 

[Carguy3J]

it also does it when its not under load...just sitting there in park it will drop below 400 rpms if you close it after being @1000 rpms

Sorry, you posted this while I was typing my "book".
Does it the stay at 400 rpm, or does it recover back to normal after a few seconds? and again, only when it's up to temp, or even when it's cold?

 

[jcwaters1]

yes it does "hunt" once in a while. and sometimes its really bad, and others it runs like a purring kitten. it just depends...on what? i am not sure. but i'm also leaning towards the IAC. are there any other tests i can do on it other then the ones you said, to be sure thats what it is before i spend $130 on a new one?

and yeah, it always does the "stumble" whether it's sitting in the driveway in park, or going slow, or whatever. but if it's at litterally 950 or 1100 rpms, then it doesnt stumble. i guess 1000 is the magic number

Sorry, you posted this while I was typing my "book".
Does it the stay at 400 rpm, or does it recover back to normal after a few seconds? and again, only when it's up to temp, or even when it's cold?

haha ya that was pretty long...good info though. its the same thing, it drops...shakes a little, then comes up to like 500 is all, so i tap the gas and it settles to approx 700 rpm. and yeah, its still only at operating temp.

 

[Carguy3J]

yes it does "hunt" once in a while. and sometimes its really bad, and others it runs like a purring kitten. it just depends...on what? i am not sure. but i'm also leaning towards the IAC. are there any other tests i can do on it other then the ones you said, to be sure thats what it is before i spend $130 on a new one?

and yeah, it always does the "stumble" whether it's sitting in the driveway in park, or going slow, or whatever. but if it's at litterally 950 or 1100 rpms, then it doesnt stumble. i guess 1000 is the magic number

No, I can't really think of anything else. I would agree, it's probably the IAC, based on what you're saying. Price wise, Autozone has it for $99, and I'm sure you could find it cheaper online. If there is a junkyard close-by, I suppose you could try a used one, but it may not be worth the trouble, and if the problem continues, you won't know if it's another bad IAC, or something else.

haha ya that was pretty long...good info though. its the same thing, it drops...shakes a little, then comes up to like 500 is all, so i tap the gas and it settles to approx 700 rpm. and yeah, its still only at operating temp.

Hmmm. I'm still leaning towards an IAC, but the fact that it only happens when warm could mean you have more than one problem. I would still do the test/temp comparison on the ECT sensor. It is also possible that you have a vacum leak that only occurs after the motor has warmed up. With the motor warmed up and running steady, spray brake cleaner, or something similar, around the base of the intake manifold, and the base of the throttle body-where it meets the intake. If the motor stumbles when you do this, you probably have a vacum leak. Apparently the SOHC are known for intake gasket leaks, as someone previously pointed out.

 

[manaen]

Yes the TPS CAN and should be adjusted follow this thread. It is a worthwhile mod
http://www.explorerforum.com/forums/showthread.php?t=79362&highlight=adjust+tps


The fact that it is only at operating temp makes me lean toward a vacuum leak. But I would still clean/replace the IAC.

 

[2000StreetRod]

ratchet routine

As I recall there is a ratchet routine in the source code for the Ford PCM that assumes the TPS voltage reading when the key is turned to On is for the closed throttle position. The value is stored and compared with subsequent readings. If a lower one is read then it becomes the new closed throttle value.

A similar thing happens with the WOT TPS reading. The PCM then scales the range for the min and max values. A scanner may read the absolute value for closed throttle as 18% but the PCM treats the value as closed throttle. The scanner may read the max absolute value as 89% but the PCM treats the value as WOT.

It's my opinion that as long as the TPS low and high values are within the extremes that when exceeded will set a DTC there is no reason to adjust the value by mechanically rotating the potentiometer.

The above may not be true for 1st generation Explorers.

 

[jcwaters1]

could it be the fuel pump?

 

[Runnin'OnEmpty]

could it be the fuel pump?

Not likely to be the fuel pump, but if yours is equipped with
an external fuel pressure regulator, check the vacuum line going to it
for cracks and such.

BTW, Dales description of the 'ratchet effect' is correct for
Gen 2 up Explorers. The PCM adjusts/ratchets for several
sensors to compensate for engine wear over the long term.
I suspect it's designed for emissions purposes.....

 

[jcwaters1]

ok, i tried spraying some engine degreaser around the manifold, and nothing happened. i'm wondering though, where EXACTLY should i be spraying? with the top cover off? or where? specifics if you would. =) thanks

 

[2000StreetRod]

IAC valve interference

Finding a leak with starting fluid and other aerosols is complicated by IAC valve interference. The IAC valve/PCM attempts to keep the idle stable reducing the effect of the aerosol. Will your engine idle with the IAC valve electrical connector disconnected? If so, try the aerosol test in that configuration. Spray the aerosol near the ports where the upper intake manifold joins the lower intake manifold and the ports where the lower intake manifold joins the heads.