Car won't idle with IAC plugged in
 

My car all of a sudden will not idle correctly, I have to keep my foot on the gas to keep id idling or it will die. I took it to my tuner who said I had a bad IAC, he said it was at 100 % and was not responding.

I noticed that I could take out my IAC and manually screw the plunger to a certain spot, put it back in unplugged and the car would idle ok. I can drive it like that and it idles right around 900-1000, as soon as I plug my IAC back in the car starts stumbling around 500-400 rpm and just dies.

I replaced the IAC with a brand new one from Oreillys and the same thing. I have tried resetting the PCM to make it re-learn idle but nothing.

I looked at the wires coming out of the IAC and they look ok no exposed wire

ttt tt

If you have access to a Snap On Modis Scanner.
Do the test where you can manually actuate the IAC.

Did you also clean the physical port on the Throttle Body?

Good Luck

My tuner tested it before I replaced the old one and said it was maxing out. The Throttle body is not dirty or gunked up.

I drove to work this morning just fine with it unplugged

If it was my car the next step would be to do continuity checks on the wires.

You like doing electrical right?:eyes:

See if there is any break between the pins from the IAC connector and PCM connector.

On top of that make sure you are getting the proper voltages at the specified pins.

Search for the LS1 pin out diagrams.

Good luck

Ok, so I replaced the IAC with a new one. The car idles fine once its warmed up right around 850rpms, but it still dies when i first start it up if I don't keep my foot lightly on the gas.

Sometimes it does this even when its warm if i turn the engine off and then start it back up. It acts like it wants to idle around 4-500 rpms. Eventually if i keep driving , it balances out to normal.

I checked for vacuum leaks by spraying carb cleaner all around the intake and hoses and no change, but i dont think its a vacuum leak or it wouldnt be able to straighten out after driving.

The Fuel filter needs changed, but its less than a year old, the Fuel pump i just replaced with a walbro

I hooked up a scanner and I can see my Throttle Position sensor likes to bounce around from 0 to .39% is that normal? Other than that the throttle readings are normal.

Fuel trims look ok around +-5%

Alternator is working fine, volts around 12-13

I opened up the Throttle blade a little by adjusting the screw, but it didn't really make any difference.

Engine Coolant Temp stays right around 190-200 once its warmed up.


The Timing is around 18 at 800 RPMS and goes up to about 27 at 12-1300 rpms if that makes any difference

bump ttt

i'm having the same problem. my car dies if i dont keep my foot on the gas when i first start it up.

after about 20 seconds, it's fine.

whats the best way to check for continuity? the length of the wire is too long for the leads on a multimeter

tested my fuel pressure today and its 50psi with the key on and 60 with the motor running, also sprayed carb cleaner all over the pcv and intake and no change

Did you ever get it figured out? My car has been doing the exact same thing.

It could be the throttle position sensor is bad. Electrical/PCM problems can be difficult to find if you don't have the equipment to test it. And throwing parts at your car gets expensive, so you're better off taking it to a shop that can diagnose it.

Yea, when it originally started i took it to my tuner, he told me my iac wasnt responding , i got a new iac the next day and when i took my old one out, i noticed it had ejected from the motor, so i replaced with the new one.

After replacing with a new one It was still not idling right and it turns out when the tuner was looking at it he left the iac values messed up from when he was troubleshooting the old one. I went back to him and He put them back like they were and it idled correctly

So Originally the problem was my IAC, after replacing the IAC I had no idea that the tuner had not put the values back like they were so I spent weeks chasing the problem.