High idle on my 2001 Saturn SL2

[xyy]

I notice that after driving my saturn for a while, if I put the gear to "N" or "P" instead of "D", the idle would suddenly increase from around 1000RPM to around 2000 RPM. Why that would happen? I drive my manu chevy Aveo, if I put gear to neutral it would always stay around 1000 RPM.

Any advice? and what treatment should I do to fix that problem?

Thanks for your help

 

[The_Jeff]

What happens if you turn the car off then start it again?

The newest saturns don't have coolant sensor issues like the old ones, but the throttle position sensors get flaky. A restart is effectively a reboot, which rezeroes the sensor at its new value.

The flaky sensor won't throw codes, usually. As part of its programming, if the car sees 1% throttle, it opens its idle speed control passage all the way for emissions/ dashpot duty.

If you want, take off the air intake tube. At 6 oclock on the throttle body you'll see the idle air bypass hole. Start the car and put your thumb over this hole. The car should almost stall or at least idle a lot lower. If you still have a high idle you have a vacuum leak somewhere.

 

[Thermo1223]

IAC

Idle Air Control

http://www.rockauto.com/catalog/moreinfo.php?pk=2396700

They usually only require a good cleaning and can be put back into service. A restart can reset it but it will get stuck again.

 

[mechtech2]

Does the idle come down after going high?
It should.
If not, the idle air valve/motor should be cleaned or replaced.
Be careful with strong solvents - plastics can melt sometimes.
So work quick or use a less aggressive sauce.

 

[xyy]

Thanks for the detail Eljefino!

I just try the saturn. If I restart, the idle did come down, but still after driving a while, the same thing happen.

For the air intake tube, is the tube connect air filter?

Originally Posted By: eljefino
What happens if you turn the car off then start it again?

The newest saturns don't have coolant sensor issues like the old ones, but the throttle position sensors get flaky. A restart is effectively a reboot, which rezeroes the sensor at its new value.

The flaky sensor won't throw codes, usually. As part of its programming, if the car sees 1% throttle, it opens its idle speed control passage all the way for emissions/ dashpot duty.

If you want, take off the air intake tube. At 6 oclock on the throttle body you'll see the idle air bypass hole. Start the car and put your thumb over this hole. The car should almost stall or at least idle a lot lower. If you still have a high idle you have a vacuum leak somewhere.

 

[xyy]

so I only need to use paper tower to wipe it clean?

Originally Posted By: Thermo1223
IAC

Idle Air Control

http://www.rockauto.com/catalog/moreinfo.php?pk=2396700

They usually only require a good cleaning and can be put back into service. A restart can reset it but it will get stuck again.

 

[xyy]

When I stop the car at light which may normally last 30s-1 min, the idle didnot come down. I think I need to clean the Idle air valve.

For the solvent, you mean use the solvent to clean the valve right? what kind of solvent I should use?

Originally Posted By: mechtech2
Does the idle come down after going high?
It should.
If not, the idle air valve/motor should be cleaned or replaced.
Be careful with strong solvents - plastics can melt sometimes.
So work quick or use a less aggressive sauce.

 

[The_Jeff]

Yes the plastic tube that goes to the air filter comes off then you see what's inside.

The car should throw a code if it's trying for one idle speed but not pulling it off. If the Idle Speed controller were sticking this would cause the code.

I still think it's your TPS, but of course, this is just an internet hunch.

 

[mechtech2]

Strong smelly carb cleaners should be used cautiously.
Brake cleaner is safer.
See if there is a resistance reading on the motor between the leads. 2-3 Ohms or so is usually good. An open means the motor is puked.

 

[Jjones]

I have a 1997 Saturn so I do not know how much they have in common if anything.Mine was doing the same thing and it turned out to be a vacuum leak.Short,maybe one inch piece of tubing, running from valve cover to intake had cracked on the bottom.One it was replaced the idle returned to normal.