I just hand my 1995 Jeep Grande Cherokee 4.0L straight 6 automatic in for tune-up (rotor, cap, wires, plugs, filters oil etc) and trans fluid service at special jeep repair shop. Also had the motor mounts and front suspension arms with bushing replaced four days after the tune up and trans service. Now after the tune-up and trans service was complete and prior to replacing the motor mounts I immediately notice more pronounced vibration in the steering wheel when stopped at a light. Take it out of gear and place in neutral while stopped at the light and it gets better but not totally gone. The replacement of the motor mounts occurred four days after the tune up and trans service with little too no effect on the this vibration. It did have a slight vibration while stopped at a light for the last few years or so prior to the tune up but now much more vibration. Jeep repair shop believes it running correctly after tune-up etc. So what is causing this increased vibration? Transmission? Want could have gone wrong in servicing the trans? Or is it more of cap, rotor, wires, plugs not agreeing with the engine - maybe try a new set of wires and plugs? Should I bring to transmission shop?
It's probably just the new motor mounts. If the new motor mounts are stiffer you will get more chassis vibration. I am a little surprised that shifting to neutral effects the vibration though. Is it automatic?
Did they have to drop your transmission cross member or any drive shafts during the service. If so it could be something to do with that.
Sounds like the clutch portion of your automatic transmission has too much friction. Happens with worn plates and burnt fluid. Often time a transmission service where they replace fluid and filter wont fix this because there can still be alot of the older sludge. In my 98 jeep grand cherokee 4.0 I have this same issue. I dumped a can of sea foam trans tune into the transmission- as it claims to dissolve dirt and sludge.
I notice a slight improvement on the first day. And after about two weeks of driving the vibrations while in gear at stop lights had almost abated. My recommendation is to run the sea foa for a month or two and then replace the fluid and filter in the transmission again. This gets expensive even if you do the work yourself. I did this process twice and added zmax transmission formula along with the fluid the second time. The issue is gone and I've saved myself engine and transmission mounts by reducing the shudder vibrations at a stoplight.
When you brought the Jeep in did you explain that you have a vibration? If you did and they suggested a tune-up was in order, you have a case to bring it back and complain. I donot believe it is related to the motor mount change,suspension or transmission work. The reason the vibration lessens when out of gear is beacause the load is removed. I think it is an engine problem. Are you getting a check engine light? It may be a misfire,vacum leak,sticking lifter or a miriad of other faults that occur on vehicles as they age. If you feel confident in the shop that did the tune-up bring it back and ask them to have another look.
Base on the limited information it's sounds like the tranny could be out of spec. This with new fluid would cause a pronounced vibration. Try to find out what fluids were use and if the torque converter was also serviced or replaced. As said, the new motor mounts would make matters worse as it puts more pressure on the rest of the parts. If these are poly or high performance motor mounts, it would make things feel worse. Again, if the motor feels strong and pulls as it should, I'm betting it's the torque converter. The convertor or flex plate could have lost the balancing weights that are sometimes welded on to balance them. The flex plate could also have cracked at the crankshaft hub.