My 740 GLE with a B230F engine has recently began to run rough at idle, acceleration and at driving speed, although at higher RPMs the jolt seems less noticeable.

My first impression was that the engine was missing on one of cylinders.

I thought it might be an ignition problem since one of the wires had some corrosion on the contact at the dist. cap and did some damage, but this wire is still firing.

I tested the missing cylinder theory by disconnecting the wires to them and this seemed to have no effect except for the very front cylinder, and this is not the one that had the corrosion damage.

If I place my hand behind the exhaust pipe, I feel a burst of higher pressure exhaust escape once per revolution. When any cylinder wire is removed except the front wire, nothing changes. When the front cylinder wire is removed however, two of these higher pressure exhaust "putts" can be felt.

I do not know if a valve can be stuck open and not make any kind of tapping or clicking sound because there is no noise of this sort.

I have recently talk to a Volvo tech. who saw the way it was running and he could not say what was wrong but said it could be due to vacuum leak.

If anyone has experienced this sort of problem or has any clues for the solution, I would appreciate the input.

Thanx.