Sorry to repeat, but for some reason my original post yesterday disappeared after just a few minutes. Recently I posted a question regarding the excessive idle speed--guessing 2000 rpm (can "idle" at 35-40mph in 4th gear)--in my '89 240 177K, 5-sp. A responder directed me to the car's self-diagnostic capability, which I then did. Here's what I found: With the test probe in the #6 hole, a 1-4-4 code (load signal missing from the LH control unit--control unit assumes the engine is at full load), and with the probe in #2 hole a 2-3-1 code (fuel system compensating for rich or lean air/fuel mixture at cruise).

I have my Bentley in hand and am prepared to do further testing, but I wanted to hear what others might think about the possible causes. My worst nightmare is a bad LH control unit ($$$!!), but if there is no hope of anything otherwise, I will have to face up to it. Here are a few details that may or may not be helpful:

1) the problem did not appear suddenly. The increased rpm happened gradually over about a month of regular driving.
2) The check engine light has come on maybe 3-4 times but always eventually goes off.
3) the engine starts and runs smoothly at all speeds. I've never had a no-start. Gas mileage is down.
4) When I start the car cold (below freezing) it used to run pretty slow and then after several minutes begin to speed up, but lately when I start it, it is screaming like a banshee in less than a minute.

I sure welcome all opinions. Thank you VERY much for taking a shot at this one.