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Discussion Starter #1
Just want to make sure it is my IAC and nothing else.

My TBird started idling around 1100 rpms and tends to creep up more and more to around 1200 rpms instead of the typical 700-800 rpms that it used to be in normal conditions. I used to have this problem intermittently, where if I shut the car off and turned it back on the problem would correct itself, but now it seems like its stuck doing this high idle thing. I can feel the car trying to move forward when I'm stopped at a light and braking is reduced since the car is trying to move forward lol. Downshifts are slightly more rough since the RPMs are staying up and I can basically accelerate lightly without having to put any input on the pedal.

I'm guessing it's the IAC? Never changed it or cleaned it.
 

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Vacuum leaks are air, right?

Hopefully that's not it, but it's pretty limited.

The only way I know of to check an IAC is to replace it.

A stuck open EGR can cause this as well.
 

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Unplug the IAC Valve and start the car to see if it idles. If it does then the IAC Valve is stuck open. A properly functioning IAC Valve will not let the car run without having to push the throttle.
 

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I had the same issue . mine was also the iac . does it go full throttle fine? If not nay be the tps.
And if its a 94-95 iac I don't think it is as simple to get at like the newer style..
Cel on ?
 

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Discussion Starter #5
I had the same issue . mine was also the iac . does it go full throttle fine? If not nay be the tps.
And if its a 94-95 iac I don't think it is as simple to get at like the newer style..
Cel on ?
My Bird is a 97.

No CEL.

Yeah it goes full throttle and drives fine, really only affects me at low speeds and idling which in turn hurts my fuel economy and makes for a quirky ride, otherwise you couldn't tell. Also worth noting is that it used to happen occasionally last winter when the weather was really cold and a restart fixed the problem most of the time, but then when summer came along it got better, and now it's fall and it's pretty much become permanent now.

I think if it was a vacuum leak I would have other issues like pinging and maybe a code, because a high idle like that would probably have to be a pretty big vac leak that would trigger at least some codes.

I'm going to unplug the IAC and see if it runs.
 

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Discussion Starter #6
Here's a video showing the high idle in drive (normal idle should be like 700) and then once you put it in neutral, jumps up to around 1350 rpms and when shifting back into drive at those RPMs it obviously causes a rough transition.
https://youtu.be/e2UuOYsZwMY

I unplugged the IAC and the car wouldn't idle, so not sure if it's still the IAC, maybe it closes but opens too much? Dunno.
 

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When the IAC went out in my 96 4.6 it did not throw a check engine light, or any codes. Mine was the opposite though, and was idling too low to the point it would stall.
On my friends truck it went out and it was doing the same as your car, again no codes.

They are pretty straight forward to replace. A couple of the bolts are in tight location but with a 1/4 ratchet and an extension its a quick job.
 

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Discussion Starter #8
Just ordered the Hitachi IAC, once it comes in I'll swap it in and see if it does the trick. Thanks guys, I just wanted to make sure if my suspicion was correct and I think it is...we'll find out.
 

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Discussion Starter #9
Alright, Hitachi valve installed today. Just gotta actually start the car and do some driving and idling now when I get the chance.

Here's pics of the old original valve I took off (hence dirtier, blacker) but I noticed some differences inside from the hole I can see the old valve had some sort of spring, new one doesn't. Old valve had a nicer paper/plastic feeling gasket on it, new valve has a plain old paper gasket. Surface finish on the new valve looks worse than the old valve, looks like they run the machining really fast on these leaving all sorts of marks, but not a critical sealing component so it should be just fine. Just some observations. Also can anyone tell me how dirty my IAC valve is? Seems to have a decent layer of deposits on it but nothing I would guess would cause any issue.
 

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Discussion Starter #10
Okay now I'm frustrated. The IAC valve made no difference in the idle of the car. Still has the high idle with it creeping up. 1100-1300 RPMs idle in park/neutral and 1000-1050 in drive. Just like in the video I posted. No change.

What to look for now?
New IAC checked off the list.
No CELs
Car runs fine with no pinging or any other signs of a vacuum leak.
 

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What does the vacuum measure at idle?
 

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Discussion Starter #12
What does the vacuum measure at idle?
I haven't measured it. But I did a few things: I unplugged the new IAC while the car was running (around a 1500rpm idle when AC is off), and my idle went down to about 500 and became rough. The car still idled. Plugging the IAC back in returned the car to its high idle again.

I unplugged the TPS while the car was high idling and it had no effect on the idle. Still a high idle. Don't know if that means anything.

Any other ideas before I borrow a set of vacuum guages?
 

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Okay now I'm frustrated. The IAC valve made no difference in the idle of the car. Still has the high idle with it creeping up. 1100-1300 RPMs idle in park/neutral and 1000-1050 in drive. Just like in the video I posted. No change.

What to look for now?
New IAC checked off the list.
No CELs
Car runs fine with no pinging or any other signs of a vacuum leak.
Make an iac restrictor plate ...I've had to use one before ..I made it out if thin plastic ..you ate just making the holes smaller to restrict the flow and it lowers rpm and helps hanging idles.
 

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Make an iac restrictor plate ...I've had to use one before ..I made it out if thin plastic ..you ate just making the holes smaller to restrict the flow and it lowers rpm and helps hanging idles.
First I've ever heard of this, let use know how it goes if you try it.

Joe
 

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To me, something like this is just putting a band aid on it. It's not solving the problem.

Joe
 

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That sucks the IAC didn't fix it. It really sounded like the problem. TPS is next, but honestly that is just my guess as well as others; that's throwing more parts at the problem.
Sounds like it might be time to get the voltmeter out and a copy of the factory service manual.
 

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Discussion Starter #20
Thanks for the input guys.

So I did some troubleshooting and threw the old IAC back on.

I had unplugged the TPS while the car was running last time and it made no difference in idle. This time I unplugged the TPS before starting the car and surprisingly....regular idle! I then plugged the TPS back in while the car was idling at regular cold idle (950 ish) and a few seconds later the idle shot back up to (1450)!

So I'm now almost certain it's the TPS. I returned the new IAC and put the old one back on since that wasn't the issue.

Ordering a new TPS as we speak, will update once I have the new one on.

Also I'm sure that IAC restrictor is for custom applications such as when you're running forced induction. Because I can see a need for that when there's more air being pushed in through the valve at idle than what is necessary.
 
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