w126 low idle in all gears

[ptrip6]

I have an issue with the idle on my '85 500 SEC. Before I start to play with any of the idle linkage, I wanted to see if anyone might be able to steer me in the right direction. Recently the car went from running fine to occasionally stalling when I would begin to put it into gear about 2 weeks ago. Just the other day the car would not start at all. After recharging the battery and starting the vehicle, I had a very high idle and reviewed some of the old post and tried to figure out the problem. I bought a new dist.cap and rotor thinking that was my initial starting problem. Turns out the battery was no good so I replaced it with a new one. I looked into the Idle control valve and I dont know if this was good or not but it seemed as if the valve was stuck in a partially opened position so I cleaned out some of the black gunk in the valve, because when I unplugged this valve connection there was no increase/decrease in RPM. Now the car starts and runs with a very low idle. Ive never had the car run so quietly. I thought this might be good, but when I went to shift into R,N,or D. there is very little idle change. Going back to check the ICV connection, when I unplug this connection, RPM do not change at all. I thought I would test drive the car and see if cleaning the ICV might have screwed something up so I drove it hard and it seems to run fine. Maybe a little slower with initial take off but no real hesitation at all. My only problem is the low idle (200-250 RPM) The mileage is coming up on 249,000 miles and I had the timing chain replaced, and heads serviced about 18 months ago. I would like to find this problem before going and spending $ on diagnostics tests... Any guidance in the right direction would be greatly appreciated.BTW, I am not good with elect. issues and need more help in that area if possible, if needed. Thanks, Rich