howie1976

I've been working on this issue for a few weeks now and have hit a wall. A mechanic friend is also at a loss as to what is causing this problem. I'll start from the beginning. A few weeks ago, my son was driving his 03 Malibu and it started to idle high, and accelerate while driving. It did it at night, all the way home until it shut off. The next morning I drove the car around for at least 20 minutes or more, and I could not replicate the issue. I took it to my friends shop, and he hooked up a scanner and no codes were present (the light never came on) and none in the history. When I went home and was about to park, it started to accelerate slightly on its own. When I put it in park, the rpms were bouncing between 1000 and around 1500. it seemed as if someone was stepping on the pedal (no it was not moving by itself). I took it back to the shop while it was still acting up (still no codes). From the little research i did, I changed the Throttle Posiition Sensor. Took it for a ride, ran fine, so I thought it was fixed. Problem came back the next day. This time it was a little different. While parked, instead of the rpms bouncing, it was stuck at 2000, and even 3000 at one point. I changed the Idle Air Control valve, and test drove it again. Again, all seemed fine for a while, but the problem came back after driving a bit. In the mean time, I cleaned the Throttle body each time I changed the 2 parts. I ran seafoam upper engine cleaner through it. Maybe helped, maybe not. I found a semi rotted vac hose from the pcv, changed that. I'm at a loss.
Sorry for the longwindedness, so here's a summary:

I'm having high-idle issues with a 2003 Malibu, 3.1L. Approx. 120k miles.

I'm pretty sure it only happens when the engine is really hot (city traffic, hot weather, never happens when the engine is cold, starts and runs fine) It's not always happening though. Currently it's just doing what it was doing before, rpms bouncing between 1000 and 1500 but will stop for a while, and start again.
I've changed the TPS, IAC, cleaned the throttle body as best I could (first with throttle body spray, then the seafoam)

Things I'm considering:
While running the seafoam cleaner a ton of white smoke comes out of the exhaust for a couple of minutes. There was quite a bit coming out near the egr tube where it connects to the exhaust. So I will probably clean/change the egr valve and tube.
I've checked most/all the vacuum lines for leaks, considering this problem only seems to happen when the engine is really hot. Not sure.
I haven't rule out the MAF sensor, but in my experience, any MAF issues usually gets a code/engine light. Same for MAP, O2, etc.
I think the alternator is on it's last leg, it's a little noise while running. I've heard this could be a culprit of problems with unknown origins. Also, maybe coincidence, but the lights were left on overnight about a week prior, and found out the battery might be bad (autozone).

So, any and all suggestions are welcome, and thanks in advance.

kevinkpk

replacing a part with a new one, dosen't mean that part is good. With your symptoms, I'd look past the tps, since the symptom hasn't changed. Does it shift ok?

howie1976

It shifts just fine. It drives great until it starts doing this.