With my engine in closed loop my IAC step counts stay around 26, while my buddies 88GT are steady around 60. What could be causing this diff? Mine is an 86. Also what voltage should I see at the IAC with the engine running? I'm trying to trouble shoot my no idle in gear problem using WinAlDl hoping to find something tangible. When we put his car in gear the step counts quickly rose to 95-105, when we put mine in gear it just stalls and the step counts stay at whatever they were. I have a new IAC, coolant sensor, plugs, base timing is set at 10 degrees, have swapped ECM's, cleaned throttle body,all with no improvement in the idle problem. In fact as of today the problem seems worse. I'm pretty much out of ideas and patience. Anyone care to have a shot at it? Forgot to mention, no codes, good mileage and overall performance. Just won't idle in gear. Oh yeah, WinALDL says tcc off, park neutral switch working right. What deity have I pissed off now?

[This message has been edited by David DeVoe (edited 05-10-2006).]

Throttle stop set wrong or a small vacuum leak will cause low IAC counts.

You need a noid light for the IAC. It plugs in just like the injector test lamps but has two lamps in it. The state of the lamps should match the IAC coil states reported by the ECM. You should see the coil states and Noid lamps flash any time the ECM is trying to move the IAC. A small vac leak can be used to force that to happen.

I believe the "Normal" range for IAC on EFI GM engines is in the 35-50 range at idle w/o load on a hot engine. This means you friend's car probably has some minor issues as well. Meaning in his case the throttle could be closed a little too much from incorrect adjustment or TB wear.

Always check with the air cleaner and any ducts off the TB to make sure there isn't some problem like a crappy filter or kinked/blocked duct killing airflow. (Unless it's some other car that has a Mass Air sensor in what case just pull the air filter and check all the ducts.)

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurasic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

Also, I suspect that the auto cars have a higher count than the manual cars.

JazzMan

Both cars are autos. I have checked for vac leaks but will check again. If I cover the hole in the throttle body the engine shuts down at once. Also the factory plug is intact on the throttle linkage so I doubt thats been played with. I will try to locate a source for the noid lights as I can see that I'm going to have to get a handle on what the IAC is doing. Thanks for the input so far.

What brand of IAC did you use ? Have you re-set the ecm after install or driven the car over 45mph to set the IAC ? Have you checked your wiring harness leading to the IAC or connector . Also check at ecm. If your friends reading is jumping that high at idle --he has a problem too--as mentioned above. The best readings you`ll get with winaldl are on a 55mph run 10-15 minutes flat road if possible, this is for majority easy readings. My first guess ---if you had not stated tcc open would be the tcc .

3800superfast thanks for the input. The reason this is making me crazy is that I've had several different IAC's in the engine, always reset the ECM, always driven the car. Yesterday we even swapped my buddies IAC into my car......no change. I've also had 3 different spotlessly clean throttle bodies on it. Another thing I forgot to mention is that the slightest load will kill the engine at idle. Coolant fan coming on will kill it for example. At all other times the engine runs great, but it absolutely will not idle in gear nor will it idle reliably when its hot. I think I may have a problem in the IAC circuit as you suggested. When I get this noid light that Ogre suggested will I be able to diagnose the circuit? I have no idea how to use one. Anyone out there speak noid?

Two thought I will toss out.

1. May not help but have you tried adding extra grounds to see if that affects the problem? Add a jumper from the bat. Neg. to the engine and see if it has any affect. (if you have not already)

2. My shade tree test for IAC's has been to pull the iac out, reconnect the plug, hold the iac in one hand with your finger(s) also holding the pintel so it does not shoot out of the iac motor. (don't want to loose the little bugger) Have someone start the car and place a finger of your other hand into the iac hole in the TB and simulate the iac to control your engine idle. You can vary the engine speed as you watch the iac drive in and out. (if it is working correctly)
If you can't do this and make it work you need to trouble shoot what the issue is. You could also log with winaldl while doing this and see what your iac counts are doing. Together doing this might get you somewhere.

Both of dodgerunners ideas are real good---would check those also. I re-read the above posts again & again , what is the winaldl showing for your volt readings ? Your saying any load brings the engine to a stall, may want to look in that area as well. Low voltage will mess with IAC and alot of other things.

Thanks dodgerunner and 3800superfast. As to the grounds, yes, I added a 4 gauge ground from the trans to the chassis that had no effect, but after thinking about it will change it to the engine. WinALDL says battery voltage is 13.6-14 volts. Alt is new, so is belt. On dodgerunners idea about holding the IAC I WILL do that. Frankly I don't think its doing much. One idea I've had is to get an IAC connector from the junkyard and make up a jumper to go around all 4 wires to the ECM and bypass the original wires in the engine compartment. Does that make sense? Downside or difficulties? I'm hoping of course that the color code on the wires is the same all the way back to the ECM so I can ID the right wires. I'm not an electrical guy but I'm almost to the point of fixing this thing or selling it, so I'll try anything. Thanks again you guys for the help.

Welcome to my hell. Awhile back I put a turbo on my DOHC, it hasnt idled since. Been over and over and over everything, to no avail. But here is what I can offer:

1: Clean all grounds, make sure extra wires go to clean metal, check the small lead off the neg on the battery. before the turbo my car would stall with the rad fan, extra ground fixed that.

2: Check it for vacum leaks, then check it again, when your positive its fine, do it again, then one more time for the hell of it. I did this and STILL overlooked a vacum leak. The primary cause of my horrible idle characteristics was air leaking by the throttle plate pivot bearing. It was actualy coming out behind the throttle cable bracket. Who would have thought !?!?! Now it almost idles but its getting there
The best way to check for vac leaks: Block of the throttle body with something, like a spray paint cap or kitty littler jug cap, something that fits snug, then tape it on. Unplug the PCV or another large vacum port and hook it to an air compressor, regulate it down to <10 PSI and open the valve. the engine should pressurize, you will get some minor seepage out like the dipstick tube, but for the most part you should be able to hear any leaks. Then spray the engine with soapy water like a leaky tire. This still didnt work for me, the only way I happened across my leak was by dumping bucket after bucket of water on the engine.

As far as the IAC, its a stepper motor, so you cant really measure the power to it, just the presence of it or not, a test lamp will work for the most part. Make sure when you are installing these, you spin the pintle all the way back until it stops moving back, and reset the ecm before you start it. Also check the passages for gunk. when you start it you want to just let it die until it idles on its own, dont hit the gas unless you absolutely cant get it to work. Then let it idle for 30+ seconds, shut if off for a few,then take it for a drive.

86GT3.4DOHC, believe me, I feel your pain. What busts my butt is driving my buddies car which has a rock solid idle, in gear or out. You can ACTUALLY drive it with just ONE FOOT!!!!!!!!! What the ...........? I intend to go back over the engine again looking for leaks, will follow your suggestions, and will also check and recheck every ground I can find.
Some fun facts about my car; I'm the second owner, guy said "its a good car but it won't idle right" I thought "big deal, needs an IAC" Changed the IAC and made it worse and things went down hill from there. That was some years ago and I've diddled with it ever since. Engine has 127k on it. Anything off idle it runs like a turbine, gets 23-24 mpg and will pull like a train from 70 to 110 with nary a stutter. Uses a pint of oil in 2k miles, mostly seeping past the valve seals. But it has NEVER idled in gear since I bought it. Anyway, good luck with yours..... we're both probably just a hair away from a solution.

If the iac will not respond in the test I suggested I would run a continuity test on the iac wires from the plug to the ecm to make sure one is not bad or grounded. Or at a minimum compare the resistant readings at the ecm between the two coils of the iac motor and to ground.

Since you swapped ecm's guess that should eliminate a bad prom.

Have you messed with air and coolant temp sensors? They play into the idle game also.

I've alway wondered what the park/neutral flag in the ecm was for. Wonder is that could have anthing to do with the idle problem. Wonder what a test disconnecting that signal would do or cause. Does the flag switch in your ecm as expected?

Just tossing ideas.....

Dodgerunner, yes good ideas. Testing the continuity of the IAC wires was what I meant I guess by jumping around them with new wires, but just testing each for continuity would probably be saner. Yes, I have changed both the MAT sensors and the coolant temp sensors. When I hooked up WinALDL this last time I made sure to look at the Park/Neutral switch reading. Switch was on in park and off in drive. I also changed this switch last fall with another I had on hand. I think before I change anything else I'm going on a big ground hunt and vac leak hunt. There is one thing that has occurred to me and thats the recovery canister for the gas fumes. There is a solenoid in there isn't there? Can it stick open?, and what happens if it does? You can tell I'm desparate now right?

Have never looked at the Fiero canister circuit. On the newer car that can cause issues so it might be possible.

Usually there is a relay somewhere that opens during the first 15-20 min. of operation to purge the canister of vapors. I'll have to see what the service manual say about how it operates. You have me wondering now and I alway have to know...

Hey if you learn anything let me know will you? Even if it doesn't apply to the current problem, any time you learn something is good.

quote Originally posted by Dodgerunner: Have never looked at the Fiero canister circuit. On the newer car that can cause issues so it might be possible. Usually there is a relay somewhere that opens during the first 15-20 min. of operation to purge the canister of vapors. I'll have to see what the service manual say about how it operates. You have me wondering now and I alway have to know...

it's pretty primitive. those 2 lines that run across the back of the car along the trunk are it. one is constant vacumm, the other is ported vacuum from the tb I think. been trying to get my system working correctly for emissions, waitin on a new canister now, as I broke the fitting on the control pot on the top. had done all the usual vacum checks, that's how I traced out the circuit and figured how it works. the bottom hardline is constant vacuum, the top seems to be ported, builds as throttle opens.

OK this is how it works..

I you look at the canister where the hoses attach there are three ports.

Two are located one above the other.
The top port is full time manifold vacuum and is used to open the purge valve when the engine is running.
Note: If the diaphragm is really bad it would be one more vacuum leak to affect idle.

The bottom port is connected to ported vacuum from the TB. This is used to pull vapor from the canister into the engine to burn whenever the TB is off idle.

The third is to the left of the other two. This one connects to the fuel tank to receive the vapors. Note this one is not used the the test below.

Testing is done as follows.

Attach a hose to the bottom port of the purge valve and attempt to blow through it. Little or no air should pass into the canister.
Apply vacuum to the top port and watch vacuum. Should hold 15" for at least 20 second. If the diaphragm is leaking the canister needs to be replaced.
If the diaphragm holds vacuum, again try to blow through the hose connected to the lower port while vacuum is still applied. You should now be able to blow into the canister. If not then the valve is bad and the canister should be replaced.

Again, thanks for the info.......great writeup on the purge canister. I have a vacuum pump and will test that little sucka asap. Did that come from the shop manual?

Yes it did.. Just re-worded it to save typing.