OK, right in the middle of a business trip, my S2K throws a CEL. Absolutely nothing seems wrong with it from a driveability perspective, so I decide to have it checked when I get back home and don't worry about it. But then, like the next morning as I'm warming up and driving off, it starts this very odd very fast oscillation at idle. The idle goes up and down maybe through a 300 RPM range or so, about 2-3 times a second. The car actually rocks back and forth side to side from the engine doing this as I am sitting in it. Now, the car is at fast idle since it is cold (20 degrees F or so). Once it warms up it seems to stop, though the CEL is on throughout.

Tonight as I arrive back home I decide to pull the ECU backup fuse and let it do the idle learn. Voila, no more CEL. I drove around for 20 minutes or so, and still no CEL.

If the funny idle or CEL come back I suppose it's off to AutoZone for a code read or to the dealer.

But in the meantime, anyone have any ideas what could be causing this? I figure that the strange idle condition must be a giveaway for some of you experts as it seems quite strange and must relate to something in particular.

Thanks!

 

sounds like a dirty/malfunctioning Idle Air Control Valve..

 

Well, I drove to work this morning (20 miles or so) without a CEL or idle problem. Apparently the computer hasn't re-detected whatever condition set the CEL last time.

Is there maintenance that can be done on the idle air control valve like cleaning and so forth? My understanding is that this valve allows for air to "bypass" the throttle so that the computer can control idle independently of the throttle position. Is this correct?

Is it within the purview of a shade-tree mechanic to replace this part if needed?

Anyone else have contrary thoughts on what might have caused this problem?

Thanks!

 

I had the same problem with an oscillation at idle. I let it go for several months just thinking that my modifications were causing the car to run rich. I got a CEL while driving home one night, but the car was running fine with only a mild roughness at idle. After many trips to the dealer it turned out to be a bad injector on cylinder number four. It was causing a miss-fire on all four cylinders. You may also check the coilpack.

Matt

 

Have a friend or the local dealership pull the Code. After you've determined the error you can approach the problem with the likely solution.

If you would like the ability to pull codes and interface with the onboard OBD2 computer, simply visit http://www.obd-2.com and purchase a cable and software package.

 

try the old whack-the-map-sensor trick with the handle of a screwdriver if it comes back....not too hard though, dont break it...just tap it a few times. Otherwise, take it to the dealership if its still under warranty!

 

Well, unfortunately it did come back. The CEL and odd idle started up again this evening on the way home from work.

So, tonight I went out and jumped the OBDII connector according to modifry's instructions and read the code.

......drum roll.....

one long, four short - IDLE AIR CONTROL VALVE!

vodalus wins the prize!

It is under extended warranty, so I can always take it in at this point and they'll fix anything on the car for the $50 deductible. But it is a hassle, as they'll certainly take their time.

Can anyone tell me if I can check anything on the IAC valve - anything user-servicable?

Matt

 

do you have an intake on the car, or recently put one on?

If so, make sure the vac lines to the sensor that was mounted to the back of the stock air box are on correct....i reversed mine when installing my intake and got a CEL, but when i switched them around, pulled the fuse, and tried again, no CEL.

 

vacuum lines might cause the IACV code, but unlikely.. I've never taken it off the car so unsure if it can be opened and cleaned properly.. at the very least, you can at least spray down the inside with carb/throttle body cleaner. (usually a temporary fix).. is your intake filter dirty?

 

1) IAC valve
2) MAP sensor
3) Dirty MAF sensor (esp with aftermarket oiled filters)
4) Vacuum leak
5) Other sensor like ECT - that has caused burps in other cars I have owned.

I agree that someone with an OBDII real-time scanner could locate this fast.