My 87 190E 2.3L vibrates at an Idle
 

I have owned my 87 190E for about 5 years, I have always had an issue of the engine vibrating the car while (( in gear )) at an Idle.
It passes emissions every two years just fine.
hear is a list of Items I have replaced trying to correct the problem.

Motor mounts. (cheap ones, then OEM ones)
trans mount
plugs/wires (Bosch)
dist. cap
fuel filter
fuel pump
fuel distributor (under the air cleaner)
camshaft/ tappets
Dont know what else to change
maybe the timing chain? the car has 280k now, I got it at 210K
If I dont put 92oct. fuel in, it pings going up hills.
I always run 92 but was told It shouldnt ping with 89.
Is my cam chain possibly stretched?

check chain stretch. may be due for it

How do I check chain stretch?