Hi

I have a 2000 Pontiac Sunfire GT with the 2.4 DOHC (manual transmission) and 200 000km.

Recently (since almost 2 weeks), my idle is now near 1500rpm instead of 800rpm and when i start the car and the engine is cold, the rpm goes to 2500rpm and slowly goes down.

Also, if I drive a gear to 3500 - 4000 rpm (or any rpm) and switch to neutral (or press the clutch) the rpm stuck here, and slowly goes down. When I stop the car, it will quickly goes down his non-normal idle (1500rpm).

I just came back from the garage where my mechanic spent a few hours looking at the problem without any success.

There was no check engine light on, at any time. He unplugged many sensors and check the vaccum hose, and the problem was still persisting and the check engine light didn't came on.


Anyone has already experienced this issues or have any idea of what is the problem? The next step my mechanic what to look at is the computer and the computer wiring.


Any help will appreciated.

Thanks :)
Guillaume

Hey. First thing I would do is get something to drink. haha

Next, there's sensors around this wonderful 2.4L, that sit all around the throttle body. You have the TPS (Throttle Positioning Sensor), the MAP (Manifold Air Pressure), and the... oh what the hell is it... it's the only other sensor on that throttle body. haha Whatever, you can't miss it.

Oh yeah, the IAC (Idle Air Control Valve).

Okay. This is where a Haynes manual or electrical manual comes in handy. These books give you specific voltages for these sensors, and we'd be able to tell if one took a dump on you. But, you COULD replace one at a time, I'd start with the IAC and see if that works (I hafve backups of all my electronics just incase something like this happens).

Also, check around the throttlebody for leaks to the vacuum lines. The 2.4 has a history of leaky EVERYTHING.

So yeah, get on that and let us know if something gets better or worse.

Hi there,

My mechanic changed the IAC, and it changed nothing, he unplugged a few others sensors and check vaccum lines around the trottle body and idle speed did not change at all, it was still around 1500rpm.

What do you mean by "The 2.4 has an history of leaky everything" ?

These things are notorious for vacuum leaks use propane or carb cleaner to locate leaks (spray around vac. lines/intake man., listen for idle change). Good luck!

Hi there, we sprayed I think it was caliper cleaner, some kind of alchool, around vacuum and there's was no change to the idle speed.

Thanks for helping, tonight after the job, i'm going back to the garage for a more in deep look at the trouble, he'll try to change the computer to see if the trouble comes from here, or from the computer wiring, wires may have some verdigris.

Thanks

You see, here's another common sense rule I overloooked, lol PCM codes. Are there ANY to this problem?

You see, here's another common sense rule I overloooked, lol PCM codes. Are there ANY to this problem?

Hum, I'm not sure I understand what you mean (sorry my english isn't very good)

Thanks

You see, here's another common sense rule I overloooked, lol PCM codes. Are there ANY to this problem?
did the mechanic read the computer for trouble codes?

yes, the only code he read was #118, which was something about a sensor he unplugged, after having it reset, the code was no longer appearing. I removed the fuel cap to see if the check engine light will come on, and it hasn't come on yet...


Thanks

I still wonder if it's maybe MAP sensor or Vac related.

i'm currently experiencing the same problem, i had to clear the computer and have it reprogrammed to get the idle back to normal. after about six months it's back again and i'm determined to figure out exactly what is causing this because the computer trick obviously is no cure.

I went back to the garage and he look at the following things ....

- Check the vacuum again, no leak
- Changed the MAP
- Changed and cleaned the IAC
- Changed the TPS

When the TPS is unplugged, the idle is OK....:lol2: , but there's a a check engine code telling the TPS is unplugged....:banghead:

He has also checked to voltage on wires and he gets 0.51 when the trottle body is closed (the book telling it's supposed to be between 0.2 and 0.9 when closed) and the when wide open he gets 4.40 (the book telling the voltage is supposed to be near 5.0)...

It looks like if it was the computer telling the sensors to run @ 1500rpm on idle ....

According to my mechanic, the issue starts from the computer, he thinks maybe the computer has been changed for a computer from an automatic car (mine is manual) or there's an issue with my computer....

What are you thinking guys?

Thanks!

Did you already clean the throttle body? I would personally do a full "induction flush" BG products makes a really good kit, but you can't buy it in auto parts stores, and you need their tool to use the chemicals.