jimmydz28

Okay, i got an 89 iroc-z 305 tpi with a 5 speed. when i start it up, drive for several seconds and come to a stop.. it idles very low, about 300 to 500 rpms lower than it should.. it will idle that low for several seconds, hunt for idle, and then come back to normal. it will really only do this any time i start up the car. it wont really do it while driving for a while.

I cleaned the egr, it wasnt hooked up the first place, but hooked it back up, no difference... changed gaskets on the runners and TB, no difference.. tried turning up min idle, nothing... This all happened after i changed my thermostat.

When i accelerate from a stop, its sometimes rough and jerky.

my car has the CCV plugged, charcoal canister removed, and i guess the egr was bypassed as well. i dont know what can be wrong.. i did cap/rotor plugs/wires last year. all fuel injectors are ticking normally as well.. help would be greatly appreciated

86T/A_Ram_Air

you might want to check the IAC valve and at the very least clean it

jimmydz28

Checked IAC and cleaned... didnt help... im discovering the low idle only happens after i start up the car.. doesnt happen randomly when driving

RedLeader289

iTrader: (2)

You could have a vacuum leak somewhere. (my appologies if whatever the acronym you have already talked about looking into refers in someway to vacuum).

You've said 2 different things: 1) that it happens when you come to a stop
and 2) that it happens only when you start the car

which is it? or is it both?

Because if it happens soon after braking and coming to a stop then that is most likely tied to a vacuum issue.

If it is when it is still warming up then it could just be getting old (I mean, it's 25 years old)

Does it die when this happens? because dropping 500 rpms from idle would be more than enough to kill most cars.

jimmydz28

Well, ill start the car, it will idle fine, but when i get down to the end of my street, prob like 15 seconds of driving, it starts to idle low, choppy, but then it kicks back up to normal after like 20 seconds.... once im driving around its fine... only happens when i leave my car sitting OFF for more than like 10 minutes... and when i get back it will do the same.. i dont understand it lol... sometimes i see the idle bounce up and down when its idling crappy, like a vac leak... but if its a vac leak, then wouldnt it be happening all of the time??

RedLeader289

iTrader: (2)

Not necessarily, and sometimes you can't tell when driving because you are giving the car gas. I'd check all of your vac. lines for problems, that's just what I think it is though. My car is carb'd so I have no experience with fuel injection on these cars.

86T/A_Ram_Air

could be an EGR issue

armos

When at a cold idle, the IAC would need to open more and flow more air than at any other time. When you drive, the throttle is open and the IAC would probably close, then when you let off the throttle and reach a stop, it would need to open again.
You did mention you cleaned it though. Did you clean out the ports, or just the IAC itself?

When it's struggling to idle, do you notice a loud whistling sound near the IAC? That would suggest the IAC is wide open (as it should be if it's having trouble hitting the target RPM).

This is a little premature and alarmist but it might act like this if you're getting oil or coolant in a cylinder. After running for a bit it burns it out and stops misfiring.
That wouldn't explain why you have to drive it a short distance before it starts missing though.

darbysan

I have found that I have trouble getting the runners and plenum to seal properly unless I use a little RTV on the gaskets. I was sure I had no vacuum leaks, but when I checked, sure enough they were there.

Also, the IAC adjustment, along with the TPS adjustment, is somewhat iterative. You need to do them two or three times in succession to get them spot on. Based on your description, I would look at the IAC adjustment , and it's easy to check for vacuum leaks around the runners.

southbay08

Just because the injectors are ticking doesn't necessarily mean that they are functioning properly. Are they stock? If so just for the hell of it test the resistance on them when they are hot and cold and see what you come up with. Let us know

jimmydz28

Well i was driving today, the idle would get stuck at a high rpm, like 1700, and the only way to get it to go back down would be revving it. now im more convinced its the IACV. But the thing is, I just replaced the IACV last year in the summer.. why would it be crapping out again?

jimmydz28

bump

86T/A_Ram_Air

Did you put a auto zone special in or a delco?

jimmydz28

i put in one at advanced autoparts, got a BWD.

im now having a feeling this is because i may fooled around with the min idle screw, and forgot to adjust the TPS.... this could explain the "hanging" idle

darbysan

I've made it a habit to always adjust min idle, TPS and IAC together. I've also found I need to do it a couple of times to get it just right, because each change to one affects the others.

jimmydz28

Just adjusted tps and IAC together. jumped A and B terminal to reset, drove for 20 min, but it will still sometimes hold a high idle when cruising in any gear and shifting into neutral. Again, i would have to rev to bring the idle back down to normal idle.. im starting to think this is now a bad IAC, but i just bought it ordered in from advanced autoparts

I have a 5 speed, if anybody is wondering.

raiderkush

Did the new IAC fix your problem? I am having similar issues on 91 305 tbi 5 spd, i turn the car off to get the idle back to normal, reving doesnt seem to work.