rblair

how do i know if the iac valve is bad on a 94 camaro z28. also how do i check the wiring on the iac and know if it is right?

Josh-'04 GTO

It only plugs in one way, so the only way the wires would be messed up is if you hacked them up at one point.

Why do you think the IAC is bad? It may just be in need of a cleaning. Take the IAC out, point the pintle down, and spray it down with carb cleaner. Don't get cleaner into the IAC motor.

Lt1t56

If IAC was defective I would guess idle high or idle low problem noticed, cleaning IAC and its passages is the best place to start. After that true test would be to watch IAC counts on a scanner.

ROLYZ28

that is my problem iac shows reading from 0 steps and climbs to 70 steps even when no load is applied on the engine.

the haynes manual says that the pintel can be moved in and out with firm presure on it but my iac seams to be very sticky even after cleaning. do you have the same senario.

Lt1t56

If engine is at running temp the IAC should have counts between 20-40 at idle, not an expert but thats what I have found from research. Warm engine at idle and IAC counts "0" there is a problem, most likely suspect vacuum leak.

ROLYZ28

replaced the iac
and the counts dropped down to below 10 steps

so the iac is workin.

i will chek for leaks

any sugestions where to start?????

Lt1t56

A vacuum gage hooked up to any of the ports should indicate leak. Stock motor should have 17-20 inches of vacuum at idle warm with no needle fluctuation.

LT1DG

Bringing this thread back to life lol. I been having similar issue, the difference is I got a A4. Everytime I come to a stop, rpm drop and car feels as if it's about to stall out. But it will recover back to normal. It's worser when it's cold outside. Sometimes it won't even do it, it's weird. Also I noticed now when I put it in drive from park or drive to reverse the freaking rpm would shot straight down then recover. Sometime even stall out but fire back up (I was thinking maybe that could be the neutral safety switch problem ?) cause the lights also dim out alittle. But the braking and rpm dropping, I think is the iac. When I checked my scanner, the counts was at 160 in drive, but when in park it settle down to like 60-65 I did a smoke test for vacuum leak, and there wasn't no leaks. My tps voltage is currently at 69 volts which is a alrite range. Everything pretty much checks out good. Which make me think it's either a tune issue or iac. Maybe that iac follower tables aren't correctly adjusted? Solomon is who tune my car.

Injuneer

Need more details:

- Year of car

- What engine mods that required a tune?

- Has it ever idled correctly since the tune was done?

- Have you addressed this problem with the tuner?

The neutral safety switch only completes the starter solenoid circuit.

- Have you cleaned the IAC? If so, did you attempt to move the pintle? You can clean with brake cleaning fluid, brush lightly, do not attempt to move the pintle, keep pointed down while cleaning to avoid getting liquid in the electric motor.

Shoebox has a simple IAC resistance check, and covers the reset procedure.

http://shbox.com/1/iac2.jpg

4th Gen LT1 F-body Tech Articles

Any work done on the throttle body before this started? I've seen one case where the gasket on the bottom plate with the IAC valve and passages was leaking coolant into the IAC passages.

LT1DG

Thanks injuneer for the response. It's a 1995 trans am and mods are cai, holley 58mm throttle body, edelbrock intake manifold, 1.6 roller, Compcam 502 cam and long tube headers.

A one point it was idling good, then this all started like 2 years ago and it's been awhile since I got a retune, so I haven't had time to tell my tuner.

I even swap the engine harness for other reasons, and the problem still there.

I bypass that already, so no coolant runs through the throttle body no more.

I haven't cleaned it yet, but clean the throttle body alittle last week and notice a little difference in idle.

And I did the reset procedure, like twice. No change. Maybe I do need to take iac completely out and do some cleaning on it.

I noticed when I clean it last week, oil is always in there. I know it's normal, but wouldn't that mess up the Iac and cause it to act up?

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Injuneer

Oil in the throttle body is often a sign of excessive pressure buildup in the crankcase. This can be due to a plugged PCV valve or excessive combustion gasses bypassing the piston rings. How many miles on the engine? It's possible some oil could get sucked into the IAC passage if the oil flow was high. Usually it just coats the blades and throttle body bores as it gets sucked into the intake manifold.

Definitely need to pull the IAC and check the condition.

It started this problem 2 years ago, after the tune, but you haven’t had time to contact the tuner???

LT1DG

The engine only has like 80k miles on it. Well taking care of, or at least i try lol.
Clogged? I hope not. I change the pcv quite often. Every oil change pretty much.

When I check it the other day, you can see a trail of dry oil going in the hole where it feeds air to the iac. I assume that could be the issue. I also discover that the hose that connects to the intake manifold and pcv on the driver side was old and brittle. I replace it, with clamps. The idle slightly got better but still the same.

That iac is kinda new, got it not to long ago. Maybe defect? I have to check it.

Nope, I haven't talk to him in quite sometime. Been busy with work, and my son. I will message him, to see if this been something that other ppl have ran into with his tune.

I read forums that ppl was have a similar issue with pcmforless years back, maybe they made some improvements since then.






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Injuneer

If the PCV valve is getting dirty enough that you have to change it "Every oil change" you appear to have a serious problem. A PCV valve can last for years in a healthy engine. When I sold my Formula after 26 years, it still had the original PCV valve, and the PCV system was functioning correctly. And that was with an engine spraying a 300-shot of nitrous = huge combustion chamber pressures/stress on the piston rings. Also was running a 58mm Holley TB. The shop that built the engine always laughed at it, and were able to show me with the engine on an engine dyno that even at 490 flywheel HP (normally aspirated) the 58mm TB was not necessary.

You appear to have excessive backflow of oil into the throttle body. Pull the hose from the throttle body to the passenger valve cover off, check for oil. Take the top cover plate off the throttle body, and see if there is oil buildup.

Based on comments I see here, and on the other LT1-oriented sites that I moderate, it appears that pcmforless has not improved with age. Nobody uses them any more. Should be very easy to tune for the limited mods you have.

LT1DG

No there still good and clean when I change them out. It's just a peace of mind habit lol. There very inexpensive, mind as well.

😂 My uncle does the same. He always joke around with me about the throttle body, cause he have his own shop and his own projects. But he always end with "At least you got something off the list" he has c10 with a 24x LT1. Also a c5

Definitely. On my day off I probably take out the iac and clean it. I should invest in catch can or something that can keep the pcv clean.

Injuneer

You shouldn’t need a catch can, because the system shouldn’t be blowing oil into the throttle body. Some people experiencing oil flow used to use a small right-angle filter from Deutsch in place of the plastic elbow in the valve cover.

One “mod” that might increase the oil flow problem is modifying the valve covers for 1.6X full roller rockers. There is a small baffle on the passenger side cover, below the hole/grommet for the PCV vent line. If that baffle is removed, it can increase entrainment of oil droplets when there is backflow in the system.