Different hot start/idle problem!
 

I've searched the previous threads for hours without finding the solution to my problem. My '90 300TE-24v (104 engine without emission control equipment) starts fine when cold, settling down from 1200 rpm to its normal 600 rpm within a minute or two. When warmed up however, it starts fine but the idle speed hunts up & down between about 400rpm and 1500 rpm, gradually settling down to 600 rpm in about 15-30 seconds. Sometimes it drops so low it stalls and has to be restarted a couple of times.
At all other times it runs fine.
I have changed the OVP relay & idle control valve to no effect.
Any suggestions?
TIA
Adrian