190e 2.3 16v engine shaking at idle (HELP)

Ok I need some real expertise in troubleshooting this problem. I brought my 190 into a very large and well known shop located in VA in order to fix a small but very annoying problem I am experiencing with a newly purchased 87 190e 2.3 16v. At idle with the engine warmed up, the car shakes as violently and feels as if the engine is moving back in forth under the hood. (motor mounts are not bad). Anyway the car was diagnosed with a bad Lamda unit as well as a clogged injector. OK - so I replaced unit and all four injectors ($450)and was told the car was running great. First thing I notice when I go to pick up the car (SHAKING). The Service Manager swears the car was running great when he checked it out merely 7 hours before I picked it up.

I left the car for some more diagnosis which included throwing in a can of 44k and asking me to put some miles on the car to see if it disappears?
At this point I feel I just paid $450 for a repair that was really not needed and mis- diagnosed and now a can of engine cleaner is going to fix it! Any thoughts or tips would greatly be appreciated.

[Benzmac]

Did the shop scope the ignition system? This engine does have resistor wire ends that do fail often. Also have the valves been adjusted lately? This is a solid tappet engine and the valves need to be adjusted every 15k miles. If the problem is on the fuel side, have the fuel distributor checked.

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM