Shaking at Idle

[Cmal]

Alright, so I've got a 95 Regal GS 3.8 liter V6. She started getting a little hot at idle so I changed the thermostat and burped the system and she hasn't run hot since. However she has started idling really rough to the point the car kinda shakes. She accelerates fine, drives smooth, and if I keep a foot on the gas and keep her over 1000 rpms the shaking stops. I'm pretty sure I got all of the air out of the system, but the very top of the bleed screw did break off the thermostat housing somehow. Also, the car has had an electrical issue for quite some time, the fuel pump was replaced about 2 years ago, the MAF sensor about a year and a half ago. Anyone have any ideas before I get the chance to get the codes? I was thinking plugs/wires, bad coil, bad motor mount or vacuum leak, but the problem started right after changing the thermostat, which makes me think that had something to do with it. Thanks in advance!

[Tech II]

Lots of places have problems reading codes for that year....

Mileage? Last tuneup? Losing coolant? Is upper plenum, black plastic?

[Cmal]

142,000 miles, last tune-up about 8,000 miles ago, yes, upper plenum is black plastic.

[Tech II]

Check fuel pressure.....

See if vehicle runs better with MAF sensor disconnected....

Check vac to F/P regulator for gas......

Check spark output with a spark tester.....

If you are losing coolant and see no external leaks, could be burning it up in cylinders due to a leaking upper plenum.....

[big white bufflo]

check for any vac leaks in the area you were working you could have broken some or nocked one off what the guy are taking about the upper plenum the 3800 are prone to melt around the egr port if you take the throtle body off you will see a tube sticking up in the manfold look aroung that if you smell coolant out the exhust