Car Revs Up And Down on its own
 

My 02 TL sat for about 4-5 months. I probably started like 3-4 times during that time. The last time I started it it ran fine for about 3 minutes than just started revving up and down. It revs down till it sounds like its about to stall and than shoots up. Up and down up and down. Even when Im driving if I just coast it does it.Im not sure what it should normally idle at but when im sitting at a red light I can feel more pressure on the brake pedal like the idle is running way to high, its at 1100rpms. I took out the IACV and cleaned it, still does the same thing.... Any Ideas?

Could be the MAP sensor, its located on the rear intake plenum.

Doubtful,

Its probably still the Idle Air Control Valve, or a vacuum leak. If the idle is reving up and down or high its usually one of those. It may also be a TPS sensor

I vote for the TPS

But that doesnt typically cause the rpms to fluctuate though. That is usually the IACV.

Yes the IACV is usually the issue but given he's cleaned that and it had no effect, guess I would get the multimeter out and verify the correct input voltage and that it is functioning correctly, but seems like there is too much of a swing in rpm for it to be the IACV. Can't you use a resistor to test it's functinality and rule it out or verify it's bad?

Take your intake tube off, start the car. On the inside of the throttle body on the bottom, there is a hole. Cover about 3/4 of that hole with your finger and see if the idle smooths out. If it does, its a good sign you have a bad IAC.

:agree:

Just because he cleaned it doesnt mean that its working correctly. First thing i would do is take some carb cleaner (in a spray can) and with the motor running is spray around the intake plumbing to see if there is a vacuum leak. If there is the idle will change.

Also there isnt too much of a swing for it to be the IACV, it can swing as much as a few thousand RPM. :2cents:

Or a bad IACV, that happened to me last year.
Mechanic checked, cleaned, nothing, had to replace the whole IACV.

Hi Guys :

I swear this has happened to me twice and BOTH times it was bad gas ! This seems to happen when I drove up north and filled up in rural areas. I think it was water in the fuel and I resolved it by topping up the tank up with new/different gas.

It doesn't hurt to try it ?

smartypants

Thanks for the advice guys, I had the same problem yesterday and I cleaned the IACV and voila, problem solved.:thumbsup:

definitely the IACV, how did you clean it, just spray cleaner in the throttle body or did you actually unbolt the IACV, sprayed the cleaner in the unit itself and verified that the shaft is turning? You might need to clean it again.

Hondas are notorious for having IACV valve stick after the engine sat for any extended period of time.

this thread saved me so much trouble.

It is your IACV valve, I had a same problem, Acura replaced mine under warranty and no more idle issues.

I went through the process of cleaning and reinstalling the IACV and it did not work. Theres a plastic screw on the IACV and I read somewhere that this screw is to tune the idle. Does anyone know if this is true?

I havent seen a plastic adjustment screw on the IACV. Dont know where you read that. If you cleaned it and it still doesnt work, its likely you need to replace it.

It was the IACV. I cleaned it once by just taking it off and spraying it down with throttle bottle cleaner and wiping it down and that didnt fix it. So I decided to take it off again and clean it good with Qtips and throttle bottle cleaner. Spent a good 20 minutes cleaning it good and that fixed the problem. I appreciate everyones advice.

I think its the TPS that lets you adjust the idle. I replaced the whole IACV and even ran sea foam thru the vacuum lines and fuel tank and the issue didnt go away. Throttle body was cleaned as well.