89 240 wagon Help

Hello,

My question is does this problem sound familiar to anyone?

I have a 1989 240 (190K miles) wagon that seems to missfire and shake at
the stop lights. It feels like every few seconds its trying to compensate
for something by knd off "catch - up rev". Its hard to explain. I will try
harder to explain.

- When i start cold, the car appears to be humming normally.
- After It warms up a bit, Thats when I get the 2 second "off purr" if you
understand my meaning.
- Then it shakes when i get to a stop like.
- It idles hard and seems like its trying to make up for the "off purr" by
idleing fast for the next second.
- Its like: brrrrr, BRRRRRRRR, brrrrrrrrrrr, BRRRRRRRR. Shake Shake Shake
Back Fire!!!
- I looked under the car and saw the whole thing from engine to exhaust
shaking and backfire'ing.

I stink at getting my point accross.

So far Ive spent $600 on tune ups, Alternator work and what I thought was a
diagnosis for the problem. But now I dont believe what the mechanic says. He
didnt diagnos the problem. He called his buddy at a volvo dealer and buddy
TOLD him what he THOUGHT it might be. Im forced to try to fix it myself But
where is my starting point??

Ben