228,xxx miles. Slight vibration at idle. What I have changed so far. Spark plugs (ngk), spark plug wires, distributor cap, rotor, and a seafoam treatment before changing out plugs. Vibration still there. The vibration did lessen a little with new cap and rotor but with the a/c on is still quite noticable. What next? Ignition coil and wire?

 

chk all the motor mounts,, mostly the rear and frt ,, the break or collapse a lot, worse with AT ..
what is the idle at??

And last DO NOT replace parts till you diagnose the issue

 

800-900 RPMs. what would be the correct way to check the motor mounts other than visually for cracks and dry rots etc?

 

Grab the valve cover & shake the engine.

Got an automatic trans? (you never said)
If so, the rear mount is vacuum-operated. Located rear-center, kinda low, between engine & firewall. Find the vacuum hose & follow it to a solenoid valve.

Have someone you trust stand on the brake pedal & shift into DRIVE or REVERSE while idling. Then you unplug the electrical wire to that solenoid valve. It SHOULD make a dramatic change to the vibration. If it doesn't, then we go through diagnosis to figure out WHY NOT.

 

Yes car is automatic forgot to state that. Will give that technic a shot thanks.

 

best way to chk the rear mount,, have car on lift,, put a floor jack under tranny or engine and rotate handle to lift up,, get a flash lite and watch the rear mount,, if broken you can actually see it separate ..

 

If there's a problem with the solenoid or with the vacuum tubing, then the mount may be OK but it's not getting the vacuum that it needs to switch between hard/soft conditions.

 

What about the timing belt? After time that gets stretched out slightly. Causing a barely noticable vibration in idle.

 

Had sometime to fool with the car today. The right hand side of the engine shakes the most with the a/c on. Vibrates more in gear but still a noticable shake in neutral with the a/c on as well. I jacked the engine up on this side via transmission and didnt see any separation of that mount. Would front or rear mount be the culprit or should I replace the right mount on the tranny side?

 

I would inspect the front mount and rear to see if they are torn or separated. Do the same method as before with the jack to see if there is excess movement from the mount you are inspecting.