Rough Idle


More Boost
Apr 8, 2002
For the past week or so the car has started fine but ran real rough and smelt like it was running real rich when cold(stock chip, thrasher went out). It even stalled on me a couple times driving down the street when cold, and about 50 degrees outside. But when the car warms up it runs perfect. Well today it was running real rough again so I gave it a little gas to try to clear it out and the rpm's wouldnt come back down and just stayed around 2000. Check engine light finally came on, came out to a code 24 (VSS) but the speedometer and all that seem to work fine. :confused: Would a faulty VSS cause this or does it sound like something else? Any help will be appreciated.
my car used to be horrible at that. start it up and it sounded like it had a very lumpy cam (i liked it:D ). it would die sometimes after running it hard, then letting out of the throttle, and sometimes just from hitting the throttle. i've been replacing vaccum lines, that helped a bit, reset the idle air controll, that also helped a bit too. it cleared up a lot all by its self too, i still haven't figured out how it does that.

start looking for bad vaccum lines, and anything that looks wrong. reset the iac and hope for the best. i was told to do some other things but i forgot what they were.
Ya I know what you mean about the lumpy cam and mine used to do that too. It does sound real tough. But it never smelt so rich or sounded like it was loading up. I just replaced all the turbo y-vaccuum hoses about 4 months ago but I should go through them all. How would I go about reseting the IAC? Thanks for the info.
i don't remember exactly what you do to reset the iac. there is a key gm made to plug into the adl port, a paper clip would work. if i remember right its the top left 2 holes, findout first, i'm not sure. then you unplug it and plug it back in? its been a long time since i did it...

Go to that site....all the info on setting IAC and TPS is there.

Also you can find out just about anything you would every want to know about your car....Read up.
OK thanks for the advice, Ill try to reset the IAC. Does anyone else have any ideas if it could be anything else? Would the IAC make the car run like that just when its cold? Does it need to be reset out of the blue like that? Or would it only happen if someone was messing with it? Cause the throttle body has never been tampered with. Any info will be appreciated.
it's just one of those things that you have to do every once in a while, at least in my experience. My car seems to detune itself, especially when I don't drive it real often.
Thanks for the input .38 Special. This car is driven everyday and has 115k miles but since you say they can detune themselves I can beleive that (too many sensors on cars today, why cant they be simple like they were back in the days?). I guess I will have to go out there and do that. The procedure seems pretty idiot-proof so I dont think theres a way I can mess it up. :p The guide on states something about adjusting the throttle set screw, but since this had never been tampered with will I still need to adjust this? Or will skipping this step still reset the IAC?
Also, I do not have a scan tool of any kind. Is it possible to do without one? The only mods are in the sig. (except that the stock chip is back in)
possibly a bad o2 sensor. they can be bad without setting a code. they respond real slow when cold, then even out when warm. sometimes they just get stuck at a certain voltage too. i had this problem with my dad's celebrity. it would idle up and down, then go up to 1500-2000 rpm, then just die. you need a scan tool to look at the data though.
You do not need a scan tool to rest it, but to adjust it you do...if you look closely at you will notice there are 2 sets of instructions.
Ya never thought about the 02 but that could very well be it. I dont think it has been changed in a while, it should be done no matter what.

As far as the the IAC goes, since I dont need a scantool and the car has not been messed with I guess reseting it to the way it should be wouldnt hurt. :cool:

Thanks a lot for the info guys. I appreciate it.
jumping the aldl (diagnostic connector) does not ADJUST the IAC. it just sets (resets) it to a certain position, as previously stated. you need a scan tool to set the iac counts, then you have to set the tps. yes, you can find all the info at sure if this is correct,but is posted by others the correct way)