I have a stock 2002 Elantra. When I take the car out of gar to come to a stop the engine revs to about 1500 - 1800 and stays there until the car has stopped, then it will idle down to normal. I've read that this can be a vacuum leak, TPS, or possible IAC. The car runs and idles fine other than the revving up, anyone have an idea of how to narrow down what the problem might be?

TIA

 

An update. I got under the hood. With the engine running, I unplugged both the IAC and the TPS alternately and with the TPS sensor unplugged it idled high, when it was plugged back in, the car idled back down to normal. With the IAC, when it was unplugged, the car idled like crap, rough and jerky. When it was plugged back in, the engine idled normal and smoothe. After that I got some carb cleaner and started spraying vacuum lines. All seemed ok. I sprayed around the fuel injectors, and injectors one and two, both, when sprayed, reved the engine up slightely for about 3-5 seconds. I ran out of cleaner and wasn't able to check three and four.

Could injector seals cause a big enough vacuum leak to cause the problem?

 

I have exactly the same problem with my 2000 Elantra manual shift. When I shift into neutral to coast along, the tach reads between 1500 and 1800 instead of dropping to idle speed of 700. At the very moment that the car rolls to a full stop, the tach drops to the proper 700 rpm.

Maybe someone out there can save me some diagnosis time on this one. Help? I'm suspecting the TPS (throttle position sensor) but would like to know for sure before buying and installing one.

 

It could be sticking throttle linkage ,TPS or a vacuum leak. Double check from the TB to the maf for lose connection. I had a bad stumble at about 1/4 throttle when pulling out in my 01 Tiburon. After some research I read the TPS can be cleaned so I removed it and used a bit of alcohol to clean it. I poured it all over the TPS ( some have a small hole from what I read , mine did not ) and gently using a flat head screwdriver worked it back and forth from closed position to wot. Maf cleaner would work better but I didn't have any on hand. After I put the tps back on the stumble was gone. Usually when no CEL is present it is unmetered air ( vacuum leak ) , a sticking throttle or sticking / corroded tps.

 

I am thinking that this specific high idle speed problem would be caused by only one specific defect. The specific key, I believe, is that the idle speed immediately drops to normal when the car is stopped. I am guessing that an over-riding control takes over the idle speed control when the car is at rest. When moving, the defective part is the controller.

I'm hoping that this specific info can be enough to pinpoint the problem without multiple testing. Or maybe someone had this same exact problem already diagnosed.

BTW, I have no CEL code items showing up.

 

If I was going to focus on one thing it would be a vacuum leak since you have no CEL.