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hey guys, I looked at my idle issues a little more and am getting confused now. well here goes. i haven't had tome to play with the car for a couple of days now. I get in today to move it to the garage and it had the usual stumble stall thing at start up but the seemed to be almost normal. i shut it off restarted and still seemed pretty good. I disconnected the iac and the idle increased as it should. plugged it back in and would not go back to idle.( bad iac you would think) since then did nothing else but I am back to the origional problem. the new and confusing part of this is I would of thought unplugging the iac would set the check eng light, but no. so i rolled the key offf then on and found the ses light is not working. not even the in the test mode key on eng off. hmmm. I may have an electrical problem. any ideas on manually checking this circuit. scan tool unavailable due to work being busy (go figure). also, how to check EGR. gm seemed to want to bury this unit under the plenum. ps, sorry for the double post ooooops

 

Do not unplug/plug the IAC with the engine running. I'm not sure why, but this gives the engine issues. Try turning it off then on again with it plugged in the whole time.

 

ok, took a break on the car cuz its bout 95 deg. out here. So I'm a jackass. I shouldn't call myself a mechanic. I took the bezel of the insrument cluster and found the previous owner took the bulb out from the check eng light. (lets not fix the problem lets take the bulb out. (right?) needless to say a little ticked off !!!!!!!! Now i might be able to pull a code and or get the scanner hooked up and find the code or codes this dummy left in this car. I hate that, customer = gee, the check eng light is on, well, Since I can't fix it i'll just take out the bulb, problem fixed (RiiiiiiiiiiiGHT?) mechanic = wrong Dumbass, it just makes people that have a clue to what they are doing to take a lot more time to diagnose what should be a simple problem. Sorry for the inconvienience to you guys that spent time replying to my concern. I say all this a little angry but, I do know nobody's perfect and when you buy a car for a short money you will get these headaches. just needed to vent some frustration. Oh well back to the Z and maybe I can see whats going on. I will keep you guys updated if your interested. thanks for all the help, hey, at least i'm getting somewhere.

 

thanks 91Z, I did not know this, I have run the car several times since then. still no change, i think the eng light and codes will give me some info too. (I'm gaining on it) LOL. something i say when things take me more time than they should. thanks man.

 

The IAC being unplugged will not throw an SES code. My IAC was bad for about 2 years and I always ran the car without it, just unplugged and tuned the car to run without it. As far as unplugging it while the engine is running, shouldn't make a hill of beans difference. It'll just be stuck in the position that it was last when the power was disconnected. Lets say that its engine hot and 15 IAC "steps" Meaning you'll have a continuous vacuum leak of 15 steps at all times. It'll make it run rough after startup until it gets warm enough to go back to where 15 steps was the prescribed amount of vacuum leak and all will be fine again.


Stumble/stall at startup on my car was associated with a bad Oxygen sensor and a bad IAC. It would act all sorts of weird when I would drive it around. I used to have to apply the gas at stop lights so that it wouldn't stall, the idle was erradic to say the very least.

Here is what I would do. Change the IAC if you haven't done so already. Make sure that you unplug the battery for this and leave it unplugged for a good 10 minutes or more if time constraints allow. Then check or even replace the oxygen sensor if you can, a new Bosch unit at Autozone will cost you about $20. I would then make CERTAIN that your TPS sensor reads correctly at idle. It should read .64 Volts with the throttle blades closed. If its not, and its reading 1V or somthing the car will think that the blades are opened and it will refrence the proper fueling "table" and apply the prescribed amount of fuel.... too much fuel in this case and it will make the car stumble and what not. TPS under .64 volts and you'll have a situation where the pedal will have to be applied to get to where it should be at idle, and will then make incorrect fuel requirement requests from the computer.

Short of these things and all vacuum lines being correct and accounted for, along with the necessity of making sure that your initial timing advance is set correctly (usually 6* advanced) with the EST wire disconnected, I'd say that it will be a mechanical problem at that point. But not likely.

 

thanks rediroc, great detailed diagnosis. i didn't think the iac unplugged while running would trip the light. but i wanted to see if it was working. which it is working but maybe incorrectly. i will check the other things mentioned like o2. i'm sure it was never replaced anyway. for 20 bucks i'll throw one in but after i check the other things cuz we all know that other things can cause an 02 to fail or read incorrect.