I have a 1995 Saturn SC2 that is misfiring and/or running rich. Any ideas of what could be wrong?

Question

I have replaced the spark plugs and wires. The fuel filter was replaced last year and I cleaned the contacts on the ignition coil pack. I noticed deposits on the EGR valve. It only has about 80k miles.

the o2 sensor has been replaced, although it was a universal one.

Answer 1

A notorious problem with Saturns prior to the 2000 model year is the ECTS (Eletronic Coolant Temperature Sensor). The tips were made out of plastic or coated Teflon and would crack under extreme heat/cold. If your coolant temperature gauge reads cool (below the quarter notch), this may be your problem. It tells your car it's running cold and constantly runs hot and/or rich in an attempt to warm up the car. The part is typically $10 to $20 and is relatively easy to change, it's below the intake and is screwed in horizontally (you'll need a 13 mm long-socket [deep well] to change it). The part after the 2000 model year changed to a solid brass tipped sensor and is not as prone to failure. I'd recommend you buy it from a Saturn Retailer, but if you opt to buy from a generic autoparts store, be sure it has a cylinderical solid brass tip. If it looks plastic, don't buy it. Be sure to replace some coolant/water as you'll lose some when you change the sensor.

Or it may be the coil packs as the previous poster has mentioned. This will show up as error codes P0340 and/or P0341. Your Saturn may be retarding the timing to adjust for bad coil packs. This will cause poor MPG performance to compensate for poor spark (high resistence). However, since your Saturn only has 80K on it, and you've already cleaned the coil towers, this may not be your problem.

If it's not throwing codes, that implies the ECTS is more likely.
Good luck. Check out the saturnfans.com forums if this doesn't help, those guys over there know their stuff.

UPDATE:
We still don't know what code you're looking at, but if it's P0171, you might want to check for leaks on the intake side and/or vacuum hoses. You may also have problems with your MAF Sensor (may need to be cleaned or replaced)

Answer 2

I don't know if this is the answer but I had customer with the same problem and they had a bad coil pack. Do you have a check engine light on? A trouble code might be helpful. Another problem with running rich could be the oxygen sensor.

Answer 3

A leaky EGR valve can cause you rough idle. with regards to running rich theres enough sensors te be considered as possible causes e.g. MAP with a vacuum line leaking or pulled out/faulty air metering sensors, coolant sensors sending false signal,oxygen sensors.Have it check by an authorised workshop/dealer.

Answer 4

If its running ruch it is most likley you O2 sencor