hello,
i really hope someone has the answer to this one. I just purchased a 1986 740 turbo wagon with only 100K on it a few months ago. it always had a slightly rough idle, the headlights flickered a bit and occasionally the voltage meter would max out for ten seconds or so then return to normal. none of the other gagues really worked at all so i didn't think too much about it. other than those things it ran great, except one problem with a faulty ground. i took it in for a tuneup at my local mechanic and it hasn't ran the same since. it barely starts, runs very rough at idle, misses excessively under acceleration, fouls plugs and spews blue smoke. they couldn't figure out what was wrong with it so i took it to another mechanic and they can't figure it out either. so far we've replaced the air mass meter, O2 sensor, idle stabilizer valve, the engine wiring harness, and have had a battery of tests run on it, all to no avail. right now i've got about $4000.00 invested in a car that doesn't work. someone please help.

Wow!

Without knowing compression specs. and other main details a lot of guessing is what you'll get. The smoke is the scary one. I'd want my money back from the ones playing process of elimination. Doesn't anyone test before they replace anymore. The fouling plugs and spewing smoke would make me: get a rebuilt engine, or get a 'good'(tested) used engine. And a dependable mechanic, one committed to Volvos.

If all else fails, add a can of compression.