Here is a '95 940 Sedan with 131,000 mi. When veh. is evenly idleing, we hear and feel a "popping" or "tremble" sensation every few seconds or so. Also, when trying to keep a 45-50mph rate, we feel a "tremble or bucking" sensation as we let off the gas. thx, MDL

Please check if the knocksensor has come loose.
This could be a possible cause of your complaint.
Knocksensor is a little square blackboxand is located on the left side of the engine block in front of the airmotor, behind the connecting hose, running to the front.
Knock sensor should be tightened to a certain value, which i dont'know off hand.

John

Thx John, this weekend I'll try to locate knocksensor and find the torque spec. Mike

Just for my info: is your airco switched on ?

John

Neg., the airco switch is not on when idle trouble happens. Thx, MDL

sounds like misfire / look at plugs for carbon traces from arcing.
(is the car tuned?)

Yes, there is carbon on the rims of the plugs. But, where the porcelin and gap area is, it is white(clean?). Should they be cleaned completly and re gaped? Also, what would creat the carbon? Thx, MDL

I would replace the plugs and wires
arcing causes the carbon traces / the power is'nt all going down the center
of the electrode (like its supposed to) instead worn ignition components
will "divert" the electricity and the carbon traces are the evidence.

Cleaning will probably not help much, I'd start with plugs and wires
and cap / rotor (on distributor) for good measure. This will establish
correct ignition operation as a "starting point" (it's maintenance anyway)

the "700/900" FAQ on this website is EXCELLENT reading almost anything
you want is listed to include valuable drivability diagnosis by symptom.

good luck. kevin walsh

Kevin/Joe, thx. It won't be right away but, plugs, wires, cap & roter looks like the best way (like you say) to begin the base point for ignition. It should be done and will in by doing so eliminate possible problem. Mike