98 S70 GLT with a few problems

[Leatherneck]

Hello. On startup, regardless of the weather, the S70 will let out a puff of white smoke. The Check Engine light is on and throwing a P0171 code. O2 sensors have been replaced and the code continues to pop up. I noticed today while sitting at the store idling that it would idle at 900 rpm's. Every once in a while the engine would "stutter" and drop to 800 to 700 rpm's for a second. I would really appreciate any help.

[JDS60R]

P0171 usually is a lean run condition based on an improper input from one of the sensors used to chose a proper air/fuel mixture.

Best paln of attack is.(stop and check if condition is repaired after each step)
1. Check and repair any intake air leaks. Listen for hissing sound while running and check all elbows and hoses for leaks.

2. Clean MAF (mass air flow sensor) with proper MAF cleaner.
This fixes it about 70% of the time.

3. Hook up a scanner with datastream and check for proper intake air , and coolant temp sensor readings .If MAF does not respond well to throtte input and code remains - replace MAF.
repalce any of the other sensors that are not within spec. (if radiator fluid reads 150 on thermometer and sensor in data stream show 180 degrees - replace coolant sensor. Same type of check for other sensors - see if they are close to reality.)

4. Put a fuel pressure guage on the schader valve (on fuel rail) and check for running pressure as well as leakdown test(turn off car and see if pressure drops rapidly = bad/dirty injector)

5. Check scope datastream for active oxygen sensor cycling betweeen .1volt dc to .9 volt dc . replace stuck or underactive oxygen sensors.

If you have a chance to service your coolant please do so. I am hoping your puff of white smok is unburned fuel rather than a leaking head gasket. A coolant flush and some Bars leak (looks like hot chocolate in a silver plastic bottle) can go a long way here.

Thats about as far as you can go at home. -Most of the time a MAF cleaning or replacement fixes it.

Wish you were in Nashville - I am still offering free help and service while unemployed.

Best Wishes on early success,
John

[PaleoDad]

I am having the exact same issue with my 99 S70. I figured I was looking at a clogged PCV system. I cleaned the MAF but the symptoms are still there. Let me know if you find a remedy.