1997 SC2 - sudden rough idle, car shakes in "D"

[chicagomike]

Automatic trans. No check engine light. I had this problem once before and the tech said maybe it was bad gasoline. I only use BP gasoline. This happened after I exited the tollway, and the car has not recovered since. The car was down to less than a 1.4 tank and I topped it off with Valvoline synthetic fuel cleaner and BP "clean" 93 octane to help clean anything. After 20+ more miles it's still bad.

In the past 3 months changed PCV valve, oil, air filter, spark plugs, oil change, trans fluid change. Throttle body was cleaned recently, and new fuel filter. All seems okay.

Car starts a little funny, idles high at first.

1. Idles higher than normal when shifting into neutral, idle seems to "hang"

2. When in DRIVE, the car shakes when at a complete stop, and the idle is fighting to keep the car alive. Let off the brake and roll forward, the shaking is a little more violent it seems. In Neutral, the problem stops because it idles higher. When you gas it, the shaking stops and it seems normal, but the shifts seem "off" like it's shifting late (it pulls to higher RPMs before shifting than it used to).

3. When slowing down, the throttle decay seems a little weird and the transmission seems "confused" while downshifting.

Is there a throttle sensor you can recommend changing before I go to Saturn to have them scan it?

[dansl2]

Sounds like motor mounts-at least you described pretty much my car before I replaced upper mount. After, it was so smooth, I couldn't tell it was running sometimes. Now the shaking is back a little & I am replacing the other mounts also. If you haven't checked at least your upper mount it is worth a second to look at. If you can slip a finger (any of them) between the metal & the rubber, it needs to be replaced. Also, if that one is gone probably the others need to be replaced also. On a difficulty scale of 1-10 about a 3 max!

[chicagomike]

Top motor mount is brand new. Bottom was never replaced. Doesn't seem like a motor mount issue since it rides a little strange and starts funny. In neutral at a stop it runs fine. The idle seems to be all over the place, like when slowing down from speed or popping it in neutral it will rev up to 2000 RPMs all by itself and hang there for a while.

Originally Posted by dansl2

Sounds like motor mounts-at least you described pretty much my car befor I replaced upper mount. Now the shaking is back a little & I am replacing the other mounts also. If you haven't checked at least your upper mount it is work a second to look at. If you can slip a finger (any of them) between the metal & the rubber, it needs to be replaced. Also, if that one is gone probably the others need to be replaced also. On a difficulty scale of 1-10 about a 3 max!

[SW1philly]

Check for vacuum leak and clean the EGR valve. I am surprised no codes are present.

[chicagomike]

I was just at Saturn. They checked it out.

No codes.

They said it's either a bad Idle Control Sensor or the EGR is getting stuck, they don't know, and they told me to wait until it gets worse or throws a code.

How do I clean the EGR? Where is it located?

Originally Posted by SW1philly

Check for vacuum leak and clean the EGR valve. I am surprised no codes are present.

[SW1philly]

It's not where mine is. I believe yours is on the engine just before the tranny near the ECTS sensor. Two bolts. Clean well making sure pintle moves. Clean with a good carb cleaner. Try not to get the solenoid on the top wet. You can use a soft toothbrush. Try to clean out egr holes on the engine with valve removed. These are "dirty" burning cars.

[dansl2]

If you changed your ECTS (yet), it is right above that. If not, drivers side approx half way back, attached to block, just below cam cover.

[chicagomike]

come on guys, I can change my air filter, spark plugs and oil and that's about it. I don't know where these things are or what to do!

suggestions?

[chicagomike]

What's ECTS? argh I have no clue about this stuff

Originally Posted by dansl2

If you changed your ECTS (yet), it is right above that. If not, drivers side approx half way back, attached to block, just below cam cover.

[dansl2]

Engine Coolant Temperature Sensor. There are a lot of posts about it on this board. The older version (2000 & earlier) had a resin tip. It tended to crack after a while & caused all kinds of problems. It was replaced in 2001 w/ a metal tipped one. It is recommended that you change yours out. Simple (easy) proceedure & cheap part. There are instructions (& pics) in the "How to" section). This might/probably could help your problem.

[chicagomike]

Ok, but I am not changing my ECTS, saturn has actually changed that a couple of times when it throws a code. I have no code.

My car has 205,000 miles on it, just trying to keep it alive. I seached HOW TO and found nothing on the EGR for my car. I just want the idle fixed. Throttle body is clean. ...

Originally Posted by dansl2

Engine Coolant Temperature Sensor. There are a lot of posts about it on this board. The older version (2000 & earlier) had a resin tip. It tended to crack after a while & caused all kinds of problems. It was replaced in 2001 w/ a metal tipped one. It is recommended that you change yours out. Simple (easy) proceedure & cheap part. There are instructions (& pics) in the "How to" section). This might/probably could help your problem.

[highwaystar]

My son's '97 is doing the exact same thing. I can't figure it out. How did you resolve this??