1988, 190E, 2.3, automatic, 99,750 miles, good looking car!

Got it about two years ago and have used it sparingly.

Feels like its running on three cylinders when idling.

Over 20MPH drives pretty good, but something feels clunky.

Replaced plugs, wires, cap, rotor and today O2 sensor. Check engine light has NOT come on like on my 300TE so I ordered an O2 sensor for each of them and the 300TE now runs perfect but the 190 still feels like it may be running on three cyls at low speeds and at idle.

Do these cars need a periodic valve adjustment?

Is there an outstanding shop manual for these cars.

I ordered the E320 Bible and for some thirty bucks I couldn't even find the torque specs for spark plugs or tires. And as for a diagram or ANY info on the Crankshaft Position Sensor...what a book!

Thanks in advance.