My 89 240 has been acting up in recent days.

When I start the car when the engine is cold it idles in park over 2000 RPM, I have to immediately put it in drive or reverse and the RPM drops down to about 1400, which is still high. If I turn it off and start it again while engine is still warm, the engine will barely idle, and check engine light comes on. This started happening recently since the weather turned cold here. This weather might be unrelated.

I did the diagnostic code and got code 2-3-1. Here is a copy and paste from the fault codes web page from this site:

2-3-1* LH 2.4 Fault Condition: Fuel trim (lambda control) too lean or too rich at part load}
LH 2.4 Causes of Fault: If too lean: air leaks, low fuel pressure, bad sensor}
LH 2.4 Symptoms: Engine stops when starting from cold; high fuel use or (or what?)

Link to diagnostic codes webpage: scroll down to chart and look at 2-3-1
http://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm#LH24FuelInjectionFault

I've had this code with a bad AMM. You can try unplugging it, then starting the car to see if it runs better, or just swap in a known good one (look for a used one).

So... you didn't mention if you actually looked for vacuum leaks or not? Remove the intake hose and inspect it and the vacuum hoses that connect to the throttle body, etc. Clean IAC and throttle body and adjust the butterfly stop and linkages per the manual, all relatively easy things to do and should fix you right up.
Charles

The first thing I would do is clean the throttle body and idle air control valve (IAC). The IAC may be gummed up and not working properly or dead, check it's function by applying 12 volts directly to it. Dan