My 940 manual lpt runs rough and vibrates a lot at idle and even more at 1500rpm. I've changed plugs, cleaned PCV, changed all filters, ran injector cleaner, etc.
The car does have a crack both on front muffler and cat, but why would it only vibrate at idle and 1500?
I'm suspecting a dirty MAF or distributor issues but i really dont know. What do you guys think?

Seems worse when it rains and today the engine cut out in the morning while idling cold.

 

If the engine is running smoothly just vibrating at idle, worse when the engine is cold - Your engine mounts have sagged and are not absorbing the vibration of the engine. When bad enough, the pan pan will touch the sub-frame. The motor mounts are pressure filled - and very soft to absorb the engine vibrations. That pressure leaks out and the mounts sag. Check your trans mount also - they are just a rubber block, but can break and cause vibration problems.

 

I forgot to mention i just changed the tranny mount recently too. It doesn't look like the mounts are bad, but not sure. Why would it vibrate only at certain rpms though? It has a small misfire too. Can it be related? Or related to exhaust?

 

You could measure the height of a new one - (if they are 10 years old - they are sagging)

 

Wad trying to check the maintenance sheet of maintenance until i bought the car. Can't find any mounts in there, but i doubt they are the original. The car is 500000km and 25yo.
i tried plugging the cracks on the exhaust recently and i believe the car was vibrating less, but putty didn't hold long. Could be coincidence.

 

You could check the clearance between the oil pan and the subframe/crossmember. Or stand on the exhaust side of the engine, (hood open) grab the oil cap. With good mounts you can move the engine left and right. With flat mounts you can't

 

I'll test them tomorrow. I tried revving while looking at the engine and it didn't seem to move much. I should have someone rev it at 1500 and see if the engine itself is vibrating more at those rpms.

 

Disregard the comments of Hoonk on engine mounts... Its not that!
check the wiring and test the idle air contril valve.
Bad engine mounts wont cause your car too stall out.
1500rpms when cold could maje the valve itself sticky.
try cleaning it after all the checks are ok

Goldenblock

 

That is true, flat engine mounts will not cause the car to stall. Flat engine mounts will cause a vibration, worse when first started and cold and that is one of the OP's complaints.