Both on my 87 and 88 4 cycl - as soon as you start the car the idle goes to 3k and stays there. On the 87 the idle will drop by about 500 RPM ever couple of min. until it gets down to 1200 RPM. On the 88 it will drop to about 1800 and stay there. I've replaced the IAC on the 88 (it would not start at all or would stay at 3K until I replaced it).

Any ideas on why I am having the same issue on two cars?

You have 2 vacuum leaks. Sometimes it is nothing more than a crack in the line or a split in one of those little rubber elbows, but it is there somewhere. Make sure the hose to the brake booster is tight.

[This message has been edited by Gall757 (edited 07-30-2013).]

check the pipe from the egr to the intake manifold--mine leaked and played havoc with me

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Pat Jones

I think I've checked all the vacuum lines and they are all tight and sound.

What would cause the ecm to send the engine into high idle at the turn of the key?

Rick, did youI check the gasket at the base of the EGR valve?

Why this topic didn't come up when I searched I have no idea. Mine started the exact same symptoms today. Vacuum leak was my first thought as well. It would have to be a pretty big leak imo.

quote Originally posted by ARKaiser: I think I've checked all the vacuum lines and they are all tight and sound. What would cause the ecm to send the engine into high idle at the turn of the key?

The only thing that the ecm can control to raise the idle is open the IAC valve, which is basically a controlled vacuum leak. You have air coming in some where: bad gasket, broken vac line or fitting, crack in egr system. Your car couldn't rev if it didn't have air, you have to find where it's getting the air.

There could be a Vac. leak and when the engine warms up it is slowly closing the leak. Is everything torqued down?

check the upper plenum for leaks.. check throttle body gasket to plenum for leaks as well.. I usually just take soapy water and brush it around the plenum and throttle body or any suspecting vacuum lines.

If a leak is present youll see it.. just make sure you dont get it on any of the electrical things

Conner

EDIT: I just saw it was a four cylinder oh well.. same idea though

[This message has been edited by gmctyphoon1992 (edited 08-02-2013).]

My egr valve was loose. That seems to have been my only issue.

quote Originally posted by TriumphFetish: My egr valve was loose. That seems to have been my only issue.

Just found that mine was also just finger tighten. I took it off and cleaned it and torqued it. After 4 or 5 restarts the car now starts at the correct RPM and dose not turn on a CES light. I'll be driving it around for awhile this afternoon and we'll see what happens.

I'm glad it was a simple fix like mine. My guess is because the bolts are in an aluminium manifold the heat cycles will tend to loosen the bolts. I plan on checking mine every couple of days for the near future.

Here is where I stand. I have tightened the loose EGR valve and replaced the IAC. I had some success. The car started and ran but again at 2500 RPM but after driving for about 20 min. (the standard reset time) the RPM dropped to sub 300 and I had to keep the throttle depressed to keep it running. Now I am right back where I started. The car right now will not start at all.

Today I took the IAC out and move it all the way in. I replaced the IAC and the engine started right off. However the RPM was back to 3000 and will not drop. I then shorten A B on the ALDL and turn the key on. I could feel the IAC pulsing. I removed the connection from the IAC and tried to start the car. No start. I took the IAC out and it was fully extended (1 1/8 inch). Cleaned the TBI and the engine starts fine with out the IAC in place but at 3000 RMP idle.

This is on the 88 and there is no check engine light.

Any ideas on what I should try next?

Are you not touching the gas when you start it? It's ok to use the gas pedal some to get it to start. It won't flood.

Ok so the IAC is moving in and out. That is good however there seems to still be a problem.

The IAC when fully extended should still have the engine running at about 500 RPM. There is a throttle stop screw with a cap over it. The problem is that it shouldn't require adjustment. But the key word is should (n't)

One thing with the IAC. If the IAC is extended beyond the normal range, when you screw it into the throttle body you will jam the pintle into the IAC. Then after that the IAC won't work.

To adjust the throttle stop screw - Start the car and let it warm up. If needed take out the IAC and retract the pintle some. Now reinstall it but don't plug it in. The car will start and idle. If you retract it all the way it will idle at 3000 so you don't want to go that far.

Once warmed up, shut off the engine. Take the cap off of the throttle stop screw and turn it in a few turns. Count them if you wish to know where it was to start with but you don't need to. Turning it in a few turns should get you to a spot where the idle is above 500. Reattach the connector to the IAC. Jumper A-B. Turn the key on, but don't start the engine. The ECM will drive the pintle out till it seats. The ECM will still be pulsing the IAC, but once the IAC bottoms out at fully extended it won't move any more. That is a normal thing the ECM does to know where the the pintle is. Wait 20 secs to make sure the pintle is fully extended. Then unplug the IAC and start the engine. You might need to use some throttle depending on how far the screw is screwed in.

Now adjust the idle speed for 500 rpm or the slowest the engine will idle on it's own.

Finally reattach the IAC connector. If you have a check engine light you will need to reset the ECM by disconnecting the battery for 15 seconds.

This should at least keep the engine from dying when the idle is surging slow.

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If at times the engine idle speed is below 500 rpm then you don't have a vacuum leak. A vacuum leak will always make the engine run fast on a Fiero. The ECM only looks at the absolute pressure in the intake manifold to calculate the gas so it doesn't matter how the air got in the intake. Throttle blades open, IAC or vacuum leak. The ECM will always inject the proper amount of fuel and thus with this set up you won't go rich/lean from a vacuum leak.

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Like I said before if you screw the IAC in with the pintle overextended it will jam the pintle and either wreck the IAC or at least temporary jam it. The same can happen when the IAC is fully retracted tightly by hand. Maybe that's why the idle stuck at 3000 rpm when you fully retracted it by hand.

Otherwise the ECM should be able to move the IAC's pintle. You have observed it moving out (with A-B shorted). The way it works, I suppose it might have problems with the ECM electrically retracting it.

You could check this by starting the engine with the IAC removed and holding it in your hand. Have the IAC plugged in electrically. Hold it so the pintle can't over-extend since if it does that spring will launch it across the garage floor and then it will just happen to fall into your floor drain. It would be best to do this with a glove on since the throttle body has coolant running through it and it gets fairly warm. Start the engine and stick your finger into the IAC hole covering up the output port to the right. When you cover the IAC output hole the engine will run slower and when you uncover it the engine will run faster. While you are doing this the ECM should be trying to adjust the idle speed by extending and retracting the IAC pintle which is now in your other hand. Make sure the ECM can move the pintle both in and out. There is always a possibility that the pintle is jamming in the throttle body hole, but it almost always gets jammed on carbon deposits and you said you have cleaned it.

I think doing the above will give you the direction to figure out what is happening. Let us know what you find.

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After the engine is warm, if the IAC can't adjust the idle to the target idle speed after 45 seconds you will get a check engine light. I don't think you will when the engine is cold however. 45 seconds = long red light. That's when mine came up with a too fast idle problem when I had a leaking EGR tube. A leaking EGR tube will never however let the engine idle down so that's not your problem.

quote Code 35 - Idle Speed Error The ECM will set code 35 when the engine speed is 75 RPM above or below the correct idle with closed throttle. This condition must be met for at least 45 seconds before the code is set. If idle speed is too high, check for vacuum leaks. If idle speed varies up and down, your engine might be running too lean (high air/fuel ratio). Check for low fuel pressure or water in fuel. If idle speed is too low, your engine might be running too rich (low air/fuel ration). Check for high fuel pressure or leaking/sticking injectors. Also, check all connections to the IAC and replace the IAC if necessary.

https://www.fiero.nl/cgi-bin/main.cgi?ECMCodes

[This message has been edited by phonedawgz (edited 08-15-2013).]

Thanks - I'll give it a try next day off I have.