Here is a strange one...IAC?

[GRWeldon]

Car died in Walmart parking lot last night. Would crank and try to start but generally would not start. Twice it started but I had to keep the revs up. Whenever I tried to bring it down slowly it would just die between 2-3K rpm. I left it there over night.

This morning, I go back and it cranks and runs just fine. I drove it about a mile home. I grabbed an IAC off one of my parts car this afternoon (its warm outside...about 85°). I installed the used IAC with a new gasket.

It cranked right up and I reved it once and it was settling in to an idle at just under 1K RPM...then it just died.

Just now I let it rest for the time it took to type this message on my phone. It would start but run rough, holding the RPM from 3K to 4K then to 5K. I let it settle down, keeping the RPM between 1000-1500. It would stay running but act like it was having multiple misfire. I let it slowly sink to idle and as soon as it hits 850, its like somebody killed the ignition. It will sometimes start but if it does it won't get above 1500 and then dies.

I have no idea what is going on. I hate to drop $50 on a brand new IAC, but if you more knowledgeable folks still believe this is an IAC issue, I'll get a new one. Only 111K miles on the engine. The donor used IAC COULD be bad...stranger things have happened. If my parts cars weren't 25 miles away I'd try another one but I've already been there once today, don't feel like going again.

Let me know what y'all think...

PS...I'm wondering if a coil pack or both might have issues...

 

[Jae 'Bird]

I am not super familiar with the symptoms but I do know that before you buy a new one you can and should try cleaning the IAC, just carb cleaner and a shop towel can get it quite clean. It is worth trying just because its free and might solve your issues, but more knowledgeable folk here can provide better input.

 

[1997ThunderbirdLXV6]

No codes? Because the symptoms resemble my crank sensor issues.

 

[GRWeldon]

No codes? Because the symptoms resemble my crank sensor issues.

I had a thought that a crank sensor failure might be a possible issue last night when she was stuck at Walmart. My code reader is also 25 miles away and when I was there today I forgot to bring it back home. Will definitely check that when I get the reader in my hands. The only time I have replaced them is when the engine has been out of the car. Are they fairly easy to do from underneath? I'll be on the ground for this, lift is also 25mi away.

 

[theterminator93]

If the IAC is stuck closed, the biggest tell that's what the issue is when you start is it will fire and briefly catch then immediately die as it sucks all the air from the plenum and manifold into a strong vacuum and suffocates. It will otherwise idle fine if you barely keep the throttle open to let in a little air for it to idle.

Try running it with the MAF unplugged to see what happens.

 

[supergordo]

Is this a 94/95 car or 96/97?

 

[GRWeldon]

Is this a 94/95 car or 96/97?

96

 

[Grog6]

To verify the iac is simple, give it partial throttle,and start it. if it runs with you giving it air, and dies when you let off, it's the iac.
I drove Lazarus for a week like that, lol.

 

[GRWeldon]

Well, sometimes it starts when I give it partial throttle, sometimes it doesn't. IF I can get it to start I ALWAYS have to do it with the throttle open. Sometimes it makes no difference. Isn't the IAC a proportional device? Can it be partially open but not quite enough to idle correctly?

In any case, it doesn't always start with the throttle partially open.

Im beginning to lean towards coil pack(s). It only seems to happen when the car is at operating temp...

 

[theterminator93]

The IAC closes completely when the car is off and no power is applied to it. When it gets stuck, that is the most common position for it. There is a small amount of air that bleeds through the throttle body when it is closed but not enough to idle with.

FWIW, coil pack failure on these is extremely rare, perhaps the most uncommon electrical failure item on these cars of all years. I wouldn't waste time or money on them, though you can do an easy spark test if you remove a plug and ground it while cranking with the fuel pump disabled.

It's more likely an issue with the MAF, ECT, IAC, CKPS, or even the wiring harness or a vacuum leak than the coils. Do the quick, easy and free test of disconnecting the MAF first to help isolate that as the cause.

 

[GRWeldon]

Do the quick, easy and free test of disconnecting the MAF first to help isolate that as the cause.

Thanks...theterminator93

Checked the codes...MAF. Pulled the plug on it and it cranks and runs. Enough to get me 25 miles to my shop where I replaced it with a new one I had on hand.

Now if I can just figure out what is causing the shudder I'm feeling. My thoughts that its the 18mo. old TC failing has been pretty much poo-pooed in another thread...