burning smell, sluggish performance 1994 850 wagon

[franckfolk]

I bought a 1994 850 wagon four months ago at 121,000 miles. After 5,000 miles of flawless driving I detected a burning/bad combustion smell on one occasion, then not again for about 500 miles, then came a second episode, then nothing. Here are the symptoms:

1) I've just noticed that the smell accompanies fits of sluggish performance. I'll struggle to get up a hill, then notice the smell.
2) The car is NOT smoking, not from the exhaust and not from the engine.
3) There's absolutely no temperature problem, nor any warning lights
4) The smell lingers. I'll park it in the garage and come back to still smell it an hour later - even with the garage door open.
5) The car has been taking slightly longer to fire up, but it eventually starts.
6) No leaks that I can tell -- certainly not on my garage floor.
7) I'm not burning oil.
The problem comes and goes. I expect that in the morning it will drive fine for another few days.

Any help would be appreciated. I'm deciding between a local mechanic or the closest Volvo guy, 35 miles away. No time for repairs myself.

[dosbricks]

Might be a bad temp. sensor causing the engine to run rich because the ECU thinks the motor is cold even after it's warmed up. Should that be the case, it ought be addressed because running to rich is bad for the O2 sensors and catalytic converter. Same goes for any fault that causes the ECU to revert to default settings.

A vacuum leak usually does not come and go the way your problem does.

I've wasted a lot of money in my earlier days taking a Volvo to a mechanic that really didn't know much about them. I've often thought I could have saved by taking it to the dealer (which we all know is not cheap). Good luck.

[smithy850]

I've got a similar smell with my '98 S70, it too comes and goes. I've had problems with my emissions system/air pump. Tonight, after the car had idled for 15-20 minutes while testing for a vacuum leak, the air pump came on and ran for a minute or so. If a bad temp. sensor causes the ECU to think the car is cold, could it also cause the air pump to run because it thinks the car is cold? If so, where is this sensor located.

[rp850]

I'd also check the PCV system as a culprit for the burning smell. What can happen is if the PCV is clogged, the oil will start to push on the engine seals and leak out. If it finds the exhaust manifold, the oil will burn off and cause the smell (especially at idle at a traffic light for example). you may never see a leak because the oil burns off before it can ever hit the driveway.

The problem about the car not starting right away could be a leaking fuel injector. The engine needs to build up fuel pressure before it can start so it has to crank a few times to do it. Pull the plugs and check for a particular plug being black or wet.