Alright I got an 89 L98 and well it starts up fine but when I m at a light the idle starts to go up and down, I've lost some power so I m thinking that one of my plugwire is burnt, I m going to change them today, I got no trouble codes so I hope thats it. Oh also I clean my IAC not to long ago any other ideas thanks.

 

Check your plug wires, connections, plugs, coil, etc...it's probably ignition related. It's also possible something is not tuned right or faulty, like the IAC. Is the A/C on when it does this?

 

I would probably chech to make sure your TPS is adjusted correctly. If it is not really tight it will move if you bump it.

 

well I just changed out the plugs and wire cap and roter, and it still does it, my tps is set at 56 volts, no trouble codes have came up I just scaned it, Oh yes it does with the ac on or off, I ll probably yank my IAC off today and check it out. It idles alittle rough too, not to bad but just enough to notice.

 

alright I think I narrowed it down, well it revs up and down at idle when I'm stopped at a light, well it does it when its not in gear ,well when it was reving I took my foot off the brake and makes the car move so is that TPS going bad?

 

With your volt meter connected to the TPS move the TPS by hand and watch the voltage on the meter. It should increase and decrease in a smooth, linear fashion. In other words the numbers shouldn't "jerk" around. They should go up and down smoothly.
Best way I know to test for a faulty TPS.
(I think its your IAC)


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Rob P
89RSconvtZZ4TPI
Edelbrock Hi-Flow Intake
SLP Dual Cold Air Intake
1 5/8" Headers
Semi-Siamesed Runners
MSD6AL/AdjFPR/IROC frnt@rear swaybar/wonderbar/steeringbox/alum drvshaft/ Alston SFC/3:23posi disc rear/MAC LCA/H.Adams Panhard Rod/KYB struts/ shocks/
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

I am having this same problem. My car runs great as long as its not idling. It starts quick and easy but it idles up and down pretty bad.
The difference in my problem is that my car will sometimes (by itself) Just idle up to like 1500 (in neutral), and stay there until i tap the gas-then it settles back down to a rough 650 rpm idle.
Also at stop lights it will be idling fine then all the sudden jump up to 2000rpm then fall below 400 then up to 2000 then comes down and dies.(this happens alomost always when it is hot)
I have checked tps and it is very linear, and set to the correct voltage. I have also reset the iac and idle screw many times. And the ignition system is in good working order.
My question to add is how to tell if your iac is bad?
Oh yeah, I never get any codes either- I don't have a scanner to check the other stuff.

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'88 RS (originally 2.8)
-350, .040 over, vette alum. L98s, stock tpi.
-305 injectors & chip
-TES headers & edelbrock cat back
-3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
on a 2.050 60 ft.
(Damn the 2.8!)