so my cars been having a problem lately where it surges (mostly on the highway) usually it won't stay steady around 2,000-2,500 rpm. It was originally giving a TPS sensor error, so i replaced the tps took apart the plenum and throttle body and cleaned it all while I was at it. Its all back together now but its still surging and idles really high when it first starts up. I tried setting the IAC when I put it back together, but my book says it involves starting the car with the idle air valve disconnected and my car won't start when that's not connected. It's not throwing any codes now but it definately doesn't seemed tuned right ...any ideas?

 

You need to have the engine warm to perform the IAC setting procedure. If the engine wont start warm during the reset procedure, Try adjusting the base idle up a bit before starting the motor. If the engine wont idle at the specified rpm, you will have to diagnose the reason before proceding. Let us know and we'll try to help.

Just for starters, most surging is caused by lean fuel mixture. EST problems, O2 sensor failure, restricted purge canister can also cause surging.

 

thanks for the quick reply. O2 sensor is new, but I'll check the purge and try setting the IAC the way u said after work tmrw ..let u know how it goes

 

Oh btw, A quick test for the purge system is to simply remove the fuel cap and see if the problem goes away.

 

ok, so it started fine after letting it warm up first this time. My book said it should be between 500 and 450 rpm but it stalls if i try and get it below 500. I got it to pretty much touch the 500 mark but not below it. The idle when the IAC is plugged in again is only a tiny bit over 600 so i think it might be close enough. It's interesting you mentioned the gas cap though, a while back it wouldn't even start up sometimes unless i let some pressure out of the gas tank. I bought a new gas cap though, and there's no more pressure so I figured that was all set.

 

The engine should be able to idle at 450 for the idle air reset. If you can get hold of a scanner, check all data itmes for a clue as to why it wont idle that low. You can check for a lean/rich condition by running an O2 sensor test. Basically you warm up the motor, run the engine at 2500 rpm for 1 minute while watching O2 voltage. It should toggle between .200 and .800. Release the throttle and let the engine idle. The O2 sensor will read accurately for a few minutes after returning to idle. If it reads low or high, you may have a fuel management issue.

The gas cap on these cars is sealed. It will pass air under high pressure or vacuum only to prevent high or low tank pressure. The tank is intended to vent through the purge canister. If the canister becomes clogged it can cause both negative and positive pressures to build. This can also cause the surging youre experiencing. I test the canister using a smoke machine. You can test it by blowing on the hose to it but I cant recommend this as a safe method.

 

sorry for the lack of updates, I hit a pretty bad pothole on the highway and had the car in the shop for a while. Finally got it back and took a look at it, the bracket holding the sway bar on was still snapped so I had to bring it back again. Now my mechanic says he can't get a hold of that bracket cuz they don't make them anymore so I have to get one at the junkyard I guess. Hopefully when I get all this sorted out I'll try checking the purge o2 test.