3000 RPM park/idle after warm and accelerates on its own

HANNAH J. DILLON

MEMBER
2002 SATURN SC1
1.9L
4 CYL
2WD
AUTOMATIC
18,300 MILES

3000 rpm in park/idle after warm up. Normal idle is around 1100.

Soon as I turn the engine over take my foot off the brake, car will start to accelerate. It got up to forty mph before I had to intercede.

Coded with P0442 EVAP Small System Leak

Check engine soon light is on.

Occasionally feel a jerk during acceleration. A few lone bucks after ten minute drive. No engine hiss, whine, sputter, no problem turning over, no exhaust smoke.

So far I have checked hoses, sprayed carburetor cleaner around, am going to clean out throttle body in the morning, which I have disconnected snorkel covered body with cardboard and engine died (no vacuum leak, right?) I unplugged the idle air control motor and idle changes. (So it is not a bad valve, right?) I know the code says EVAP leak, so vacuum leak is somewhere, but nothing fits the runaway car? Will double check cylinders one and two gasket tomorrow as well, going to have help getting in there better. I checked exhaust pipe for signs of coolant leak, nothing. Dipstick may have a hint of gasoline. Will probably change oil tomorrow as well. Will have second nose check stick and also check spark plugs, I did not have a tool to reach them.
But was hoping for a few leads? Am I on the right track? I have scoured YouTube, Googled, I cannot find anything like my problem. So help please!

5 Replies

HARRY P

MECHANIC
2,292 POSTS

I would bet on a leaking intake manifold gasket. At least that is what I would check next. A small leak there can cause that high idle. Here is our general vacuum leak guide: https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Use that process to check the intake gasket.

Also, use this guide to do another check on that IAC motor. Personally, I would suspect it and check it before checking the intake gasket. https://www.2carpros.com/articles/engine-idles-too-high

As for the EVAP leak, the most common cause of that is a worn out gasket/seal on the gas cap. Spend $10.00 on a new one and clear the codes to see if that takes care of that.

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Saturday, September 22nd, 2018 AT 8:22 PM

HANNAH J. DILLON

MEMBER
3 POSTS

Okay, so odd thing. I was ready to replace the IAC, decided to wait and try cleaning the carbon off it first. Was doing another check for vacuum leak. Flashlight popped the throttle sensor and the idle fluxed. So I tap it again. Check mate. Took it off. Went to auto shops, none in stock. Go home put it back on, now my idle is back to normal and my car is no longer accelerating on its own! Now, I can hear the vacuum leak, sounds like it is from the throttle. Ran out of time running around. Cleaning out throttle shortly, hopefully that is where the vacuum issue is.
This has been driving me nuts, never checked the throttle sensor, checked everything but.

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Monday, September 24th, 2018 AT 7:09 PM

HARRY P

MECHANIC
2,292 POSTS

Hmm interesting. I would not have thought about the throttle sensor either since it was not throwing a code.

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Monday, September 24th, 2018 AT 9:23 PM

HANNAH J. DILLON

MEMBER
3 POSTS

I know, I am scratching my head, but glad I did not start spending money on the guessing game that was about to begin. Hopefully, after today's cleaning, my EVAP code goes away too.

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Tuesday, September 25th, 2018 AT 1:55 AM

KEN L

MASTER CERTIFIED MECHANIC
48,356 POSTS

I have seen the PCM go bad and cause this problem as well. I would try a used one because there is no code for this problem to tell us for sure. Here is the location. Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

Cheers, Ken

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