960 24v Auto 4 Door Saloon - 61,000 miles - Petrol - 1st August 1995

Car shudders when engine warm in P or N drive - Okay in D or R drive - Okay when cold. Drives and changes gear perfectly, until you stop and select P or N. Initial thought was a dose of Redex Injector Cleaner - however always use Shell Unleaded - early days for a Redex result. In meantime was thinking low auto transmission fluid. Not sure if auto transmission fluid ever changed. I took car over from my late father in July 2013 at 36,000 miles. All service records thrown away by my sister! The car has towed a caravan in its early life, now only a single horse trailer. A solid car which has sailed through 4 MOT's.
Any suggestions?

 

Not sure how severe the shudder is - ie if its the transmission trying to engage or if you have a motor mount issue being exposed at idle. For the mounts, give a visual look around then work with a buddy to put the car in gear with full brake and give a small amount of power to see if the engine rocks or lifts in an odd way.

For the transmission, I'd start by checking the level and color of the transmission fluid. Check out Volvotips.com for procedures etc. Since Volvo doesn't demand a fluid change in the maintenance I'd assume it has not been done and consider doing a drain/fill with clean fluid - just make sure you use the correct fluid spec'd for your car or a compatible synthetic. The other component that could be in play is the PNP sensor (park-neutral position sensor for the shifter) which can be out of adjustment or failing. Quite often the contacts in the switch corrode and can be cleaned up a bit with a "shifter row" (park to lo to park 20x fast). See if that activity changes anything. You can also try moving the shifter a tad while the car is running to see if that alleviates the shudder.