Ok, 1990 firebird 3.1, about 100k, auto trans.

At idle, nearly always in drive and way more
often when hot, I get a vibration/roughness.

In neutral, nearly never, and nothing at any vehicle
speed.

No codes and decent maintence history.

Tranny seems ok, no significant slip and shifts nice.

What do you folks think?

Engine mount, tranny mount?

Cylinder not firing intermittantly?

No significant noises...

Looking for input.

Joe R

 

I would suggest motor mounts and timing chain if you havent tackled those items yet.Motor mounts are not fun unless you have a lift and possibly remove the lower pass.arm to gain access to the nuts.I did mine on the ground cussin and fussin them on/off.Timing chain has a guide/dampner between the cam and crank gears and its not a high quality chain either.So checking chain slop while watching the dizzy rotor doesnt do anything.The excess just hits the dampner and gives you the impression its okay,found that out after my water pump went out and just went after it anyway.And as always a better set of injectors ,as the OEM's suck.