300E rough rough rough idle

I love this site. I have learned more in 1 week of reading here than I could have learned in a month of Sundays elsewhere.

I have a 1990 300E with a 103-983-12-206201 engine. We have had the car since it was a baby and it is a part of the family. We have taken exceptional care of it. The following is a list of what I have done with OEM parts since the first of the year.
*Removed/inspected/cleaned intake
*cleaned clogged EGR (exhaust gas recirculation) tube
*Replaced all injectors/insulators/o-rings
*Replaced all filters (except power steering)
*Replaced all brittle vacuum lines
*Replaced dist. cap/rotor/plugs(not platinum)/plug wires
*Flushed coolant replaced water pump/overflow tank/rad.cap
*Replaced drag link/tie rod ends/ brakes/shocks
*Installed Euro-Headlights with leveling system (with your help)
*New tires/4wheel alignment
*Rebuilt Starter (just because) same with alternator/regulator
*Installed block heater (what a waste of time- burnt up first time I plugged it in.)
*Changed all fluids/filters (transmission/rear end ect.)
*Replaced reference sensor (old one had a crack but worked)

Now I have the roughest idle known to man. Cold Start is fine but once it warms up it will jar your teeth out at a redlight. Although my dentist is smiling, I am not. I removed the OVP relay and resoldered every joint on it.

My Question;
Is there a way to check the function of the idle valve off of the vehicle? Being the Dennis the Mennis that I am you know that I have already tried. I may have fried it. I applied 12vdc and it opened. When I removed the 12vdc it closed but not all the way. Was not all the way closed before I applied voltage though. When I had the intake off I inspected the bottom of the fuel/air dist. for cracks. (none) I have since inspected for a vacuum leak. Can't find one.

I am getting ready to replace the timing chain, tensioner, oil chain. I thought about going ahead and doing a head job but really do not see the need. No smoke, No fluid loss- coolant or oil. By the way..This car just turned over 150,000 yesterday. The motor is as clean as it was the day I got it---maybe cleaner.

Can you help..I have made a genuine effort to find my answer using your search option. I have learned a lot but nothing that I feel would help.

P.S. Fuel has been flushed and treated- -twice. I am also going to replace the Oxygen sensor (never been changed). I found a great article about how to set the stiocyometric (not sure of spelling) ratio. Lambda point. Using a John Fluke rms87 multimeter I used the #2 and #3 pins on the x11 connector. Setting the average battery voltage at 50% +/- 10% proved futile. The reading at 2500 rpm would stabalize and them move up 1volt/sec to battery voltage, hold for two seconds and then decend 1volt/second to zero. I hate to replace the Oxygen sensor until I find out what is causing the rough idle...Might mess up the pre-cat or the catalytic convertor.

Please forgive my spelling, run-on-sentences and sentence structure. Us Boys from Tennessee just started wearing shoes last year.....you can't expect too much too soo.

Thanks in advance
Michael Granger