IAC Questions

[natenkiki2004]

I have a 1991 v6 Ex with 230k miles on it and when I got it, it had severe starting issues. It would never start the first time you cranked it. It would start the second time but even that was a little shaky. After some troubleshooting and tuneups, I found that the Intake Air Temp sensor was extremely faulty and replacing it made the Ex start right up.

Right after that though, I developed another issue. When cold, the idle would hunt around a little bit, surging up past 1K RPM and then heading back down to 800 RPM or so. It would do this until warmed up. I cleaned the IAC before replacing the IAT sensor (I found that thread with pictures) but didn't use a new gasket when installing. I also used carb cleaner NOT electrical contact cleaner (oops...).

Fast forward to today, the last couple of times I start the Ex, it really stumbles and has very low RPM for a few seconds, to the point of sounding like it's going to die. Running some errands today, I restarted the Ex when warm and it seemed a bit shaky but not nearly as bad when cold. I got home and pulled the IAT and IAC. The IAT tests fine for now (I'll check more later) but I'm a bit confused on the IAC readings.

Looking at this thread:
http://www.explorerforum.com/forums/showthread.php?t=232262

I should have 2 different readings when probing the pins, depending on polarity? I get 9.7 ohm no matter which polarity I probe with. That's 9.7, not 9,700. As far as I can tell, this IAC is stock (the previous owner replaced a lot of parts with non-OEM aftermarket ones and this has the FORD logo).

Does my IAC seem fried? Perhaps I fried it with carb cleaner or maybe it just bit the dust after 230K miles?

Thanks.



Forgot to mention, my IAC looks like this:
http://i.fixya.net/fixya20/uploads/images/jturcotte_524.gif
Not the one shown in the cleaning thread:
http://www.explorerforum.com/photopost/data/503/3661iac_before_low_res.jpg

 

[malohnes]

There is a diaphragm that could have been rotted that can cause the IAC to fail, regardless of the impedance check. Carb cleaner could damage it as well, but thrush be told, that is how I clean mine. Mine is also original and acting flaky these cold winter days.

 

[natenkiki2004]

I didn't think the carb cleaner would hurt it much. I didn't let it soak and blew it out with an air compressor after cleaning the immense amount of crud out. Then again, maybe the air compressor screwed something...

The issue with hunting/surging on a cold idle only came up after I swapped out the IAT sensor and fixed a major vacuum leak. Maybe the vacuum leak was doing the job of the IAC valve? Or at least masking the problem with a high idle?

I'd hate to go and drop $100 or so for a new unit (NAPA's higher-end model) just on a guess/shot in the dark.

 

[natenkiki2004]

More info: I read on the newer years you can test the ohm from either pin to the case and it should be over 10K ohm. I get nothing at all.

 

[natenkiki2004]

Well, I decided to backprobe the TPS since I read that can cause idle problems as well but I'm more confused now...

I have 4.85v on the ref and ground pins with the TPS unplugged from the harness.
Plugging the TPS back in and probing the sig and ground pins, I get -0.84v at idle and -4.67v at WOT.

I've checked the connections several times, my polarity is correct and the multimeter has a fresh battery and tests fine on several other connections. Would a faulty TPS send back a negative voltage? It seems like the values are ok but the polarity is wrong...

 

[malohnes]

Not sure on the negative voltage part, but the voltage value is a little low from ideal. Idle should be around .96v and WOT at 5v. I think this could be part of the problem. There is a TPS mod that shows how to set the TPS to ideal.

TheRangerStation has some info on the TPS mod also.

I'm still thinking IAC is chief culprit.

 

[natenkiki2004]

Not sure on the negative voltage part, but the voltage value is a little low from ideal. Idle should be around .96v and WOT at 5v. I think this could be part of the problem. There is a TPS mod that shows how to set the TPS to ideal.

TheRangerStation has some info on the TPS mod also.

I'm still thinking IAC is chief culprit.

I did see that mod and I'm tempted but 1 thing at a time The throttle response seems great and smooth with plenty of power and no hesitation. When the Ex is running when warm, there's no stopping it. It's a solid performer. It's just cold starts and cold idle that I've been fighting on and off now.

The IAC not having a pin-to-case resistance reading seems pretty suspect. Should be 10K ohm for Explorers '91-'01 according to my Haynes manual. I'm gonna see if the local auto parts has one in stock I can probe with my multimeter. If not, I may just order the $85 unit with 3-year warranty and be done with it.

 

[malohnes]

You have a good point. The mod is for throttle response, but my truck actually helped clear up some idle issues. The response part was a side benefit for me.

Thinking more on your dead reading, I wonder of the connector itself is at fault. Connectors are made of plastic and many time the plastic fatigues and breaks apart. You might be able to pull the pins out of the connector and take a look, and take another reading with your meter, but I am not positive about that. I played with my TPS and MAS sensors this way.

I'm not sure that compressed air would hurt the IAC any more than carb cleaner, but I would think that if the diaphragm is getting old and weak, it could very well damage it. Too bad it is not a cheap part, say like a temp sender

 

[natenkiki2004]

Well come to find out, despite knowing a bit about electrical systems, a reading of no continuity on the multimeter can mean infinite ohms. Apparently this is greater than 10K ohm and according to Ford, that is within spec. I had to find this out on a non-Explorer, non-Ranger forum after Googling quite a while. No reading = good for pin to case measurement on the IAC. With this info, mine tests fine, at least the coil for the motor. I just find it odd that I had to hunt around for this info because it's not blatantly stated in the Chilton, Haynes or anywhere on here but yet I've seen a lot of confusion on here for that specific measurement. Even people going and buying a new IAC and have no improvement after installing it.

Ever since I disconnected the battery to reset the computer, the Ex seems to run pretty decently. I got a new IAC gasket coming in since I've re-mounted it a few times with the original gasket. When it comes in, I'll give the IAC another cleaning and call it good.

I've pulled codes and have nothing new, just a persistent 57 for the trans neutral switch which I'll worry about later.

 

[FR-425]

Hey check this out:

I think your PCM "believes" your engine is up-to-temp ALL the time.

It's the PCM temp sensor!

This dude will also cause rough idle on warm restarts as well and contribute to lean/rich probs, poor fuel econ, and other nasty tuning errors.

The one "near" The housing for the PCM looks like this.

It is a bad Temp sensor.

http://www.rockauto.com/catalog/moreinfo.php?pk=951148&cc=1119631

Been here, done that already on the 94.

There are (2) sensors, so make sure you change the one that has a cone on the end of it, next to the thermostat housing.

 

[FR-425]

May be worth a look at your cold air damper (if so equipped..)

If your Ex is equipped you will have two vacuum lines connected to the top rear of the air box.

It switches when cold to draw hot air off the right exhaust manifold until the PCM detects "minimum operating temp" and goes off open loop. Then the door opens to cold air inlet.

If it's busted, well --- = bad cold starts.

If it is not getting vacuum it will always be in the cold air position.

If everything is in order. Check the foil tube that runs from the exhaust manifold to the air box.

I admit this is getting a bit to picky because it is really only intended to help warm up the engine quicker for cold environments, but I have noticed shaky performance for the first 10 minutes without it.

A bad diaphragm in here will provide you with a cold start vacuum leak causing a lean cold start.

 

[FR-425]

Carburetors! remember those?

Get the choke set right and cold be *^^%$ed.

 

[FR-425]

Seems like these sensor glitches always happen in three's.....??

Until they add up to a trouble-shoot exercise in grey hair and arthritis of the brain.

 

[natenkiki2004]

FR-425, thank you for getting me reading and thinking!

I already replaced the IAT sensor which was the cause of a major startup issue (lean cold starts) and the ECT sensor (the one you posted) seems fine although I will test it hot and cold tomorrow.

However, reading that thread that you quoted the info from, it got me thinking and so I decided to go out and poke around on the Ex (at 10:30PM) and I don't know how I missed it before but I found another vacuum leak. One of the plastic tubes coming off the tree was worn in half, I assume by the trans kickdown or throttle cable rubbing that wasn't stuck in the cable holder. As far as I can tell, that specific tube either goes to the air box or to some component on the fuel system (I'm guessing the fuel pressure regulator). Although, I don't think I see either of those items in the vacuum diagram I have.

In any event, that's #1 priority to get that bugger fixed and check for others as well.

 

[mr cribb]

I may have to look into these parts.

I suspect my IAC is shot due to high idle upon cold start (1500 rpm), and rough idle kind of choking/ stumbling out on warm restarts (600 rpm).

I am getting a consistent 18.5 mpg on the highway (and 98% of it is highway per tank), but comparing to my old 2wd that got 22 mpg (4 door 3.27 gears), I feel like I am missing 2 mpg on my current 4wd (2 door 3.73 gears).

I keep my speed to between 65 and 70 which is 2400 to 2500 rpm.

Whenever I fuel up, I am putting in 17 to 17.5 gallons.


I am open to suggestions.

 

[smegun]

after doing a typical tuneup new plugs wires checking alternator i replaced the AIC with the crank sensor the block temp sensor and cleaned the MAF this wasnt the major problem its a tolerant part you probobly have to trust that it is a tolerant part I replaced the O2 sensors too .... the truck has to be warm or it wont burn all the fuel its normal but still the best thing for performance i did was put in a bottle of chevrons complete flush the little black bottle on top of about 8 gallons of gas made short trips for a few days letting it rest it gave me 25 percent more efficiency those jets need a dose nothing else worked sea foam short lived berrymans coats the sparkplugs with gunk the chevron product works if you want to try it techroleen soap

truck is tuned hot evidently it runs good for awhile after reaching operating temp but then could use a cold shot of air later in the day ..it runs better at night when the temps are cooler thinking of a cold air intake but seems situated well stock its probobly a problem im having with the truck detuning on the fly with the cam position sensor the sensors run together in circuit to tune the truck the AIC is part of the problem but so is fuel

my truck dosnt have a knock sensor so in part im questioning the theory of the circuit of sensors and how they relate to the full stroke of the truck .....bummer my next trick is to question the cam position sensor itself its built into the distributer type unit behind the engine

taking out the octane resistor and drilling holes in my catalytic converter to find bliss ive taken out the resistor once seems like the truck gets torqueyer but havnt done a full trial with it out

i know the truck runs good at times but lacks a 4 barrel carb it just cant seem to handle burning all the fuel being given it when trying to pass even high test

obd1 sucks without a conversion i want to find my detuning gremlin could be O2 air seems like temp air at night but everything ive ever driven at night seems better

latest from ford is short phlenum gas evaporates to fast direct to head with pressure there still trying to do it turn gas into gas leave it hangin around the right ammount of time my buddie took off his highrise double webbers to a standard holly worked perfect at least he can drive gas is evaporating fast im looking at my milage since gas hitting 250 a gallon i seem to be loosing maybe they found a new light formula and its cheaper :/ methanol and alchaholly ...:/ there selling us the new bark formula just not telling us


ive been playing with relays lately and am questioning

 

[natenkiki2004]

Boy oh boy this is a revival. For what it's worth, I've learned a lot in the last year but I still have this issue.

IAT and ECT sensors replaced and tested within tolerances. Cold engine starts still falter, I've learned to deal with it by giving it gas while starting, that usually does the trick. I'm tempted to still buy a new IAC valve, they can be found cheap enough on eBay. But I think part of the issue may be injectors or bad check valve in the fuel pump. Sometimes it seems like my fuel rail is empty but priming extra times (key on, off, on, off) doesn't always help, it seems like there's something else going on.

I haven't given this issue much thought as there have been more pressing things to fix on my Explorer. I calculated my MPG to be 14.2 over 1,500 miles so something is still off. MAF & TPS seem fine, no need to replace. O2 was replaced too. That doesn't leave much left, except the IAC. If anything, my plugs look on the lean side and having to give it gas when starting it cold may mean that the IAC is leaking too much air into the engine. Hasn't thrown any check engine lights on me though.

I will say that my other suspect may be a bad lower intake gasket which might be sucking excess air in. I know I have issues with coolant leaking from the lower intake, so the intake ports themselves could be leaking too? That's on my to-do list.

I will figure it out in due time.

 

[1Byounkin]

Mine had a crazy miss show up thinking it was all of that stuff. Finding out I had one spark plug die. Wasn't even that old. I spent over $100 trying to figure it out. Had no power and sucked gas. I replaced that plug, power came back. Might be worth looking in to. The simplest things can be missed. More of the things that will not throw a code.

Good luck

 

[natenkiki2004]

I bought new plugs for it when I got it and have pulled them twice in the last 2,000 miles, they all look identical. I replaced the wires too with some Belden lifetime ones, not long after I got it.

I will be replacing the plugs once I made a parts order, I'll get some Motorcraft double platinums. Not that I need them but I found a few sources that have them cheaper than Autolite coppers so... why not?

All that said, I don't think plugs/wires are the issue in my case.

 

[1Byounkin]

That's good.im trying to think how I got past that. I've had that had before.

So basically it runs rough at operation temp. With bad mpg. Right?

Have you done any checking of the FPR? See if the vacuum line has gas in it. That can suck gas strait into the engine.