when i start my car the idle jumps up to 2300, then slowly comes down, this also happens anytime i put the clutch in or put it in neutral. its not as bad once the car is warmed up, but still does it. i have gone over every vacuum hose and they are all intact. i have also replaced the IAC valve ( i have an 88 2.8L) i also replaced the MAT sensor. any thoughts?

 

Hello....

very friendly site......

 

Doc,

When you replacd the IAC, did you clean the air passages in the throttle body where teh IAC is mounted?

 

yea i cleaned out the throttle body and the entire intake.

 

Doc,

A few other possible hidden leaks can be the PCV valve, EGR valve, and power brake booster. It's fairly easy to cap teh PCV and brake booster lines to test that theory, but the EGR valve may not be do easy to diagnose.

Also, IIRC, the IAC on a V-6 requires a learning procedure when replaced. They aren't just "plug-and-play" like a V-8 IAC. As I recall, they need to be monitored for IAC counts and the pintle position adjsuted accordingly. That may have been only on the '90 and later V-6s, but I'm not sure of that.

If you search by "V-6" and "IAC" you might find something I posted earlier.

 

i checked w/ two different older GM techs and they said the 88 2.8 does not have a relearn procedure. we went through the Tech1 and there is no relearn procedure in there. so they suggested to disconnect the battery. i left it off over night to reset everything. still the same.

 

Here's one of them:

https://www.thirdgen.org/techbb2/sho...hreadid=149505

 

Doc,

Obviously, you're way ahead of me on this one. I'd guess that the two Techs are right, and the IAC needs no special procedure as the later ones do.

Do you have an idle (well, whatever idle happens to be) RPM and vacuum reading? Your problem is screaming "vacuum leak". You may also have an issue with the throttle body, but I'm guessing you've already checked that out, too. Did you disconnect the throttle cable, cruise cable, and transmission TV cable just to make sure they aren't binding?

 

ok heres what i have, the idle jumps up when i first start the car. it goes up to like 2300. then it SLOWLY comes down. eventually it reaches normal idle speed. but anytime i put it in neutral or push in the clutch, it jumps up and then comes back down. when it goes up, it takes anywhere from 10 to 30 seconds to come down again. its not as bad when its warm but its still a problem. anything else you can think of to check? i have replaced the IAC valve and MAT (manifold air temp) sensor (which was bad) i have visually inspected the vacuum lines, which doesnt mean a whole lot. i guess, aside from a bad vacuum hose, what else could there be? my next step is to pull the plenum and redo the whole vacuum hose system.

 

Check. I got all that before, except the part about it eventually reaching normal idle RPM. It certainly sounds like a sluggish IAC, but since you've replaced it, that makes TWO of them that have the same symptoms, and all but eliminates that as a possibility.

Since you have a couple of factory trained techs at your disposal, you might want to inquire about the IAC rate. I also have a vague recollection of there being two different IAC step rates for V6 engines. Then again, that may have been the same difference as the "plug-and-play" versus "learned" IAC types.

Do you have a scanner that can read IAC counts?

 

What about the valve adjustments?. Cause for strange accelerations at idle, too.

 

ill check with them after this weekend and see what they say about the IAC steps. its not even a huge deal but it gets annoying, lol.

 

oh dennis, its not the valve adjustments. it has no problems idling, just takes a while to get down to idle speed.

 

I have this exact same problem down to the clutch making the idle jump to 2600 rpm. I can't figure it out myself, I just got my car running and when I start it the idle will jump to 3000 rpm and slowly come down, but I heard this is normal, its warming up the engine and will idle normal.

But when I am on the road if I put the clutch in the idle jumps to 2600 and slowly comes down, its like a 50/50 chance it will do it. Im suspecting my brake booster vacuum line. I accidently left it unplugged when I started the car once, car would idle to 2600 and drop and idle back at 2600.

Im gonna dedicate a day or two to investigate this, if I find anything i'll let ya know.

 

about the only thing i can think of anymore is possibly MAF sensor problem. im trying to get ahold of the one off my grandma' s (yea my grandma's) camaro. i have a strong feeling that could be my problem, since i also have a really rich running problem. but thats partially because of injectors leaking, blah blah blah. how is your MAF as far as you know?

 

No clue, im not sure if im using a MAP or MAF or have a way to test it. I have a 91 3.1 Vt 5-spd. Does it use the MAP or MAF? I believe its the MAP but not sure. If there is a way to test it i'll do just that.

 

Replaced my Map, no longer do I get a long high idle when starting the car, it does jump to 3000 rpm but comes down much quicker, not to mention my idle is now smooth and the rpm will not rise when putting the clutch in. Just FYI if you stiill have the problem.

 

well i unhooked mine and then started and drove it. it was lots better, throttle response was great, just a bit of fluctuating w/ the idle, i assume from not having it hooked up. so im thinking im going to get a new one for it.