My 91 Firebird I just purchased has a really bad idle when the car warms up. It goes from 500 rpm to 1000 and back and forth. I replaced the IAC and another small snesor just under it. Neither did the job, as a matter of fact now when the car is warn and restarted, the idle jumps up to 2000 rpm's and slowly comes back to normal. When the crusie control is set or just going at a steady pace you can feel the car surging up and down. The car has 95K on it and has never been tuned up or any after market mods. It runs very well except this problem. Any help is greatly appreciated. Thank You Very Much !!!!

 

You may have a vaccuum leak somewhere.... take some throttle body cleaner and spray it along the base of the plenum and runners, and any other vaccuum lines you can find, listen for the RPMS to drop, and that is where a leak is.

Does/has your engine light come on at anytime?

 

No engine lights what so ever, even took it to the dealer, ( yes I know, what a joke ) they told me as long as no codes are being produced they cannot figure out what to do. I'm guessing since the check engine light isn't coming on. Thanks again

 

Oh, well they are extremely stupid then. I brought my GTA to the dealer this past season with a power problem... the car just WOULD NOT pull past 4000RPM, lots of people said, thats TPI restrictions... I said.. NO WAY!!!

Anyway.. I had NO CODES at all coming up... since I was determined something was wrong, I told the dealer mechanic to take it on a test drive and hook up the diagnostic computer and see what the engine is doing while driving... anyway, they found that the TPS was only reading 1.42 Volts at Wide Open Throttle... It is suppose to be around 4 volts... so my car was thinking it was at half throttle. The mechanic then tested the computer output to the TPS and it still read 1.42 Volts, thus meaning it was either the computer or the wire(s) going to the computer. He checked the wire, and it was fi ne, so he replaced the computer (250bux brand new)... needless to say, it ran like a top after that, shaving 1.5 seconds off the 1/4 mile, and giving the ability to smoke the tires any time I choose, and sometimes even when I didn't want to.

So.... either find a new dealer, or take it back and say that you want a driven computer diagnostic check and check all the parameters of each sensor.. it should only cost about 100bux canadian... so 60 american I think.

Try to find a vaccuum leak before you take it in though, cause that sounds like your problem... seems that the engine is getting air from somewhere else, causing the IAC valve not being able to do its job.

 

250.00 for a computer?? I should start selling the stack I have.

-- Joe

www.joesperformance.com

 

Are the ones you have brand new AC Delco replacements? And note thats in canadian dollars

 

A couple of things...

first the computer isn't going to know when the fuel pump starts to crap out, or when the injectors are flaking out, etc... as long as it doesnt see a rich or lean condition you aren't going to know if you have a fuel problem.

Aside from that your problem doesn't sound fuel related. I'd say you've got an IAC problem. You've replaced the motor, probably didn't need it but you didn't say if you reset it correctly. Go here: https://www.thirdgen.org/newdesign/tech/tpimod2.shtml Forget about the TPS it doesn't really matter since the SD cars don't have to be adjusted. Follow the minimum air instructions. In my case I didn't have to adjust the throttle adjustment screw at all. When I started out the car idled at about 1500rpm, afterwards it idled at the correct 600rpm. It also took care of a stalling problem that I had anytime I came off the interstate. Give it a try its easy, I'd start here.

If the problems continue look into the things you should do anyway. Cap, rotor, plugs, wires, fuel filter, 02 sensor, PCV valve, air filter, etc. If you want to use high performance parts thats fine but delco and the over the counter stuff will work fine too. Also see if you can get your hands on a timing light and check your timing. If the car isn't in tune you can't start to troubleshoot a problem. There's a good chance that any of these could be your problem, and doing the entire lot shouldn't cost you more than $50 with normal parts.

After that I'd check your fuel pressure. You'll need a guage ($30). If its not supplying the correct pressure or holding pressure you could be looking at a bad regulator, fuel injectors, or fuel pump. Also don't rule out electrical problems, wiring, ecm, etc.

The GM dealership just didn't want to work on an older car. Doesn't matter much anyway, makes more sense to learn your car and do the work yourself.

 

Thank you everyone for all the suggestions, i have a blown 72 chevelle w/454, tools and such are not a problem, except, there are a heck of alot of additional sensors on this thing. I think I will try the basic tune up first and check for any vacume leaks and go from there, I like the suggestion that the dealership dosen't want to work on it anyway, probably very true. Are their any hints on getting the plugs out of this thing, do you have to go under the car to get any of them out ???

THANKS AGAIN FOR ALL THE REPLYS !!!!!!

 

Plugs are easy. Go to the tool box. You'll need a spark plug socket, a 3" extension, 6" extension, and a 3/8" drive ratchet.
Start at the front on the drivers side, the first three should come out from the top. Then jack up the car, support with jackstands and slide underneath. You should be able to get the last plug on the drivers side, then move on to the passengers. The crossmember is going to be in the way, and you probably won't be able to see most of the plugs. The hardest part is getting the plug boots off the plugs. You will have to see with your hands. This works best with the car cold cause you'll be putting your arm/hand near the block and manifolds, etc. Snake up over the crossmember and work from the front back... the ratchet and 3" extension with socket will be all the more you'll be able to get up in there. Just take your time and its pretty self explanatory.

 

thanks very much, i'll be trying all the suggestions over the weekend coming up.

 

my car did that when the fuel pump was going out....