99 SL1 Saturn Runs Rough

I have a similar problem with my 2000 SW2 (manual shift). I brought it to a shop for a routine tune-up, and when I got it back it had problems. Tune up included new plug wires, re-gap existing plugs (I asked them not to change them since I put new ones in recently), change of air filter, oil & filter change, checking existing fuel filter & keeping it because it "looked fine".

The overall symptoms are loss of mileage (~25 mpg down from ~35), hesitation when accelerating, especially when first entering a higher gear, and occasional stalling when slowing to a stop and putting it in neurtral. One very strange thing is that the hesitation/stalling problems only occur when the engine is WARM. It's perfectly normal first thing in the morning.

I've read elsewhere that the engine temp sensor could be bad, but I have my doubts in this case. The temp guage goes to its normal spot, heat works as usual, etc. It seems as if something else isn't working right once it gets the temperature data.

I took it back to the shop that did the tune-up, but they couldn't find what was causing the problems.

There were no codes when I went to Autozone, but later I did get a code lasting for a few minutes regarding the Throttle Position Sensor (TPS). So I got some spray cleaner (the stuff made specifically for fuel injected cars) and cleaned a lot of gunk out of the throttle body, but the problem still exists.

Maybe it's the TPS itself, but it seems like an unlikely coincidence that the TPS would happen to go at the same time that a simple oil change or routine tune-up was done. It seems more likely that some gunk was dislodged in the system somewhere as work was being done, and the gunk made its way downstream, landed on a sensor, and is now fouling things up. Sort of like a blood clot causing a stroke.

I'd like to check & clean more of the sensors, but my Haynes book has not been overly helpful for this problem (although it's been great for other things I've done).

Any idea how to get diagrams for the car's computer system -- component locations, wiring diagrams, etc? Helm's was recommended

but I'd like some feedback from other Helm customers that have used the book for troubleshooting the computer system & sensors.

Thanks.

A good shop manual that gives information on the OBDII codes and of course a code reader are very helpful to have. Helm publishes the shop manuals - same ones that the dealer uses except that the dealers have the on-line versions.

TPS sensors can get noisy. It's basically the same idea as the gas gauge sensor or the volume control on your old-school table radio. Moving the sensor shaft moves a wiper against a resistance element. Over time the contact between the moving parts wears and becomes erratic. This gives electrical noise which the computer doesn't quite know how to make sense of. Sometimes you can put voltmeter on the TPS and slowly move it over the full range. Attach the meter from chassis ground to the output terminal on the sensor (terminals are ground, 5V and output). voltage should be proportional to sensor position and stable for any position. Not an expensive part, they are usually more simple to just replace. Drive by wire systems have dual sensor elements on both the throttle pedal and throttle actuator for redundancy. Oppie

I have a similar problem with my 2000 SW2 (manual shift). I brought it to a shop for a routine tune-up, and when I got it back it had problems. Tune up included new plug wires, re-gap existing plugs (I asked them not to change them since I put new ones in recently), change of air filter, oil & filter change, checking existing fuel filter & keeping it because it "looked fine".

The overall symptoms are loss of mileage (~25 mpg down from ~35), hesitation when accelerating, especially when first entering a higher gear, and occasional stalling when slowing to a stop and putting it in neurtral. One very strange thing is that the hesitation/stalling problems only occur when the engine is WARM. It's perfectly normal first thing in the morning.

I've read elsewhere that the engine temp sensor could be bad, but I have my doubts in this case. The temp guage goes to its normal spot, heat works as usual, etc. It seems as if something else isn't working right once it gets the temperature data.

I took it back to the shop that did the tune-up, but they couldn't find what was causing the problems.

There were no codes when I went to Autozone, but later I did get a code lasting for a few minutes regarding the Throttle Position Sensor (TPS). So I got some spray cleaner (the stuff made specifically for fuel injected cars) and cleaned a lot of gunk out of the throttle body, but the problem still exists.

Maybe it's the TPS itself, but it seems like an unlikely coincidence that the TPS would happen to go at the same time that a simple oil change or routine tune-up was done. It seems more likely that some gunk was dislodged in the system somewhere as work was being done, and the gunk made its way downstream, landed on a sensor, and is now fouling things up. Sort of like a blood clot causing a stroke.

I'd like to check & clean more of the sensors, but my Haynes book has not been overly helpful for this problem (although it's been great for other things I've done).

Any idea how to get diagrams for the car's computer system -- component locations, wiring diagrams, etc? Helm's was recommended

but I'd like some feedback from other Helm customers that have used the book for troubleshooting the computer system & sensors.

Thanks.

chance are it is the tps, runs good at high rpm sucks at low rpm! If it was a vacuum line it would idle high as verses come down to low idle. The ts will be very erractic at low speed and almost kill the engine. One other dangerous area is the plug gap. I had excellent gas milage until I changed the plugs on my vehicle, gapped them at 40 per spec so what was wrong? Well the milage turned out to b the point gap.. mine are now gapped at 49-50 which increased my milage and ALWAYS use standard copper type plugs. The 1.95 type of autolite or ngk to work the best. Platiums always fail in a saturn!

Well I took the car in to the shop. Turns out we had a couple of clogged fuel injectors. The diagnostic codes indicated that the car was misfiring, and that it had a lean condition. Which makes sense if the engine is not getting enough fuel from the injectors. At any rate, they were able to run some injection cleaner through the system and now it is running much better. Better than it has run in a long while.

chance are it is the tps, runs good at high rpm sucks at low rpm! If it was a vacuum line it would idle high as verses come down to low idle. The ts will be very erractic at low speed and almost kill the engine. One other dangerous area is the plug gap. I had excellent gas milage until I changed the plugs on my vehicle, gapped them at 40 per spec so what was wrong? Well the milage turned out to b the point gap.. mine are now gapped at 49-50 which increased my milage and ALWAYS use standard copper type plugs. The 1.95 type of autolite or ngk to work the best. Platiums always fail in a saturn!