Mechanics

INCONSISTENT RPMS

1998 Saturn SC1

Engine Performance problem
1998 Saturn SC1 4 cyl Front Wheel Drive Automatic 127000 miles

I have a problem that has stumped the so called car experts I know. Whenever my car is idling or going up a hill or basically under load, the RPMs jump all over the place and the car shakes. This will only happen when the car is in drive or reverse. Park and neutral don't have the problem. Also, it isn't as bad when the engine is cold. I've already replaced the spark plugs and wires and got the injectors cleaned out. These didn't seem to have any effect (Although I did need to have it done anyways). Now I'm wondering what my next step should be because I don't want to waste more money just tracking down the problem. The check engine light isn't on and I suspect transmission problems as I've had them in the past with this car.
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Wtfrara
November 20, 2009.




Will it act up idling in gear at a stop?I would start by checking ur coolant temp sensor unplug it and look amd see if theres coolant or corrosion in the connector it pretty common for them to go bad and there under 20 to replace. Let me know what u find.
Louie

Saturntech9
Nov 20, 2009.
Yes, it's acting up while in gear. My fix lately (so I can still get to work) has been to pop it into neutral at a stop. Can you explain why the temp sensor would cause this?

Tiny
Wtfrara
Nov 20, 2009.
When the sensor goes bad they usually read too cold of engine temp or they will go from like 180-210 in a matter of a few seconds. When the engine is cold it likes the extra fuel as it warms up it needs less fuel so if the sensor reads colder then it's suppose too when the engine warms up it's running too rich and runs poorly.I have a 99 Saturn sl2 the temp sensor just went bad or was going bad it would idle high sometimes the idle would bounce all over or when I came to a stop the car would die or come close to dieing. While I was driving it was surging felt like it was going to die.I watch the engine temp with the engine off and it was bouncing up and down like 20-30 degrees changed the sensor and it ran awesome.I have seen those sensor do so many differnt things when they went bad sometimes I even thought no that cant be the sensor doing that and come to find out it was. Hope this helps u. Let me know what u found.
Louie

Saturntech9
Nov 20, 2009.
I replaced the temp sensor about 2 years ago. It was the middle of summer and I couldn't start my car because it was getting too much gas. Since then, I've watched the temperature gauge pretty closely and it doesn't seem to be doing the same thing. Then again, it is about 30 degrees out right now and the gauge doesn't get too high on the short drive to work.

Tiny
Wtfrara
Nov 20, 2009.
I checked on the drive home. The gauge was working just fine. The temp sensor doesn't make sense in this case since the problem is only occurring in drive and reverse. More specifically, it happens at 900 RPM (idle) 1500 and 2200

Tiny
Wtfrara
Nov 20, 2009.
Like I said when the sensors go bad they do all kinds of differnt things like when mine went bad it idled fine when it was cold and in neutral and park when I put it in gear it had the problem. Also I got the car a couple of years before that and replaced the sensor with a brand new saturn one and I never even noticed anything strange about the temp gauge operation and I have worked for saturn over 16 years when u have only one temp sensor for the gauge and computer makes it hard to detect a problem with it watching the gauge even with the trained eye.I liked it when there was two sensors one for the gauge and one for the computer then u could see the fan come on at the proper temp on the gauge and if it didnt u knew u had a problem. Iam just saying not everything is as it seems or as u think it is I have been fooled or miss lead by thinking oh it cant be that I just replaced that part or that couldnt cause that problem and it did. Really without watching the temp on a scan tool and using a temp gun to watch the differance till the fan comes on and see that its not more then 10 degrees between the gun and computer we really cant rule out the sensor. Ok lets move on u need to check for vaccuum leaks starting with that hose that goes from ur valve cover where ur pcv is to ur intake they get holes and cause the car to drive like u swear u have a transmission problem first one I had I swore it was the transsmission also make sure ur pcv is good if u take it out turn it up side down and look at the valve part of it it should be all the way closed if it is open at all it is bad has a weak spring. Then start the car up idling in part get some carb spray and spray around the intake vaccuum hoses throttle body etc and see if u get a rpm increase or decrease let me know what u find.
Louie
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Saturntech9
Nov 21, 2009.

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