My volvo runs great. starts great. 238k miles. just intermittantly smoke will come out of the tailpipe, one can kinda tell when it is going to do it because the idle will change to sligtly rough and rpm will drop a bit, kinda like loading up or something. Put the car in neutral, and rev the engine, the smoke goes away for a while, then it will come back if still at the same location is idle. On the freeway or driving at any speed, the car has absolutly no smoke. Please help. (turbo drain has been replaced, intercooler drained, turbo seems to be in good shape --lots of power and no smoke under hard acceleration -- im stumped).

you probly wont see any smoke while driving as it is being shot out of the tail pipe at a high rate of speed, Sounds to me like you have a leaky turbo or ring. You may also have a failing head gasket, those are the things i would check at this point from the description you gave.

Thank you for your feedback. I have had someone drive behind me and no spoke is apparant. This smoke at idle think pretty much bellows out when it decides it is going to do it. If I had to guess myself, I would point at excessive crankcase pressure -- intermittantly (causing oil to not drain from turbo or pushing oil past valves. This is why I think I will do a leak down test to see if I might find a bad head gasket or cylinder rings. Thanks again!

How much oil are you burning (loosing)?
What weight of oil are you using ?

Culprits: Turbo O-rings, Head gasket or head itself (warped),
Piston rings, valves or valve guides, bad timing.
Good luck !