My 99 sl1 is idoling high when I put it into neutral, but it also seems a little harder to get stopped. The check engine light is not on. Does anyone have any ideas as to what might be causing this problem?

 

Clean the throttle body. Also, spray some throttle body cleaner around the area between the throttle body and the intake manifold, and around where the intake manifold meets the engine block, with special attention around the #1 cylinder. The design of the SOHC intake manifold is lacking in support around #1. The result is often that the intake manifold gets partially sucked in, creating a vacuum leak in the process.

When you spray the cleaner around, you're listening for a change in engine idle. If the idle changes when you spray in a certain location, you've located the vacuum leak.

Please let us know what you find.

 

I agree with derfs suggestions 100%.

 

I believe that cleaning the throttle body did the trick. Wow, it had so much build up on it. Going to drive the car a little more before I turn my wife and kids loose in it. Thanks for the info on this problem.

 

When my car is put into reverse or drive the car idols rough, but when I put the car in neutral the car idols smooth. Thoughts?

 

Which model car do you have Richard? It may be missing in neutral and you cannot feel the miss until you put it in gear. How does it do going down the road?

 

When my car is put into reverse or drive the car idols rough, but when I put the car in neutral the car idols smooth. Thoughts? Derf if you see this my car idols rough at low rpms with my foot on the brake.

 

Richard

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We know you have an SL1 or SL2, but ....
2) Please do not post related issues in multiple threads or in multiple sections of the forum. It makes it next to impossible for us to help you b/c diff people will respond to different threads and no one will see it all. I've merged your 3 threads into one.
3) As for the rough idle, I think you may be feeling the effects of a failed upper torque axis mount (fancy name for top engine mount). These are consumables on S cars as the engines vibrate quite a bit, and the engine is constantly trying to rotate (laws of physics). The torque axis mounting system is designed to keep the engine from excessive torquing. The upper takes the brunt of the abuse.

When the upper mount goes, you usually feel the vibrations in the cabin the worst at the lower rpms.
Drive and reverse are at lower rpms than neutral, plus the engine is not under load in neutral.
Open the hood. Standing in front of the engine, the top mount is just to the left of the valve cover and is shaped kinda like an upside down U with rubber across the inside.
Check the rubber carefully for cracks, tears, disconnection from the supports.

Also. try to fit a ball point pen or your fingers between the top metal piece and the rubber part. If you can, the mount is worn out.

Get an OEM mount from a GM dealer. Aftermarket is cheaper....and crappy from what I hear. Be sure to get new studs and nuts as the design of the mounts changed, then changed back over time. Getting new ones ensures they are the correct length for the new mount. And do NOT overtorque! They WILL twist off.

 

It runs fine going down the road.

 

Checked that engine mount and I can just about get my fingers between the rubber part and bracket. Believe that it needs replaced. Thanks again for the help. I will let you guys know if it fixes my problem.