I've watched a few threads below that were talking about fast idle. I broke out the old Bentley last night to see how to adjust the base idle on my '89 only to find that LH2.4 systems do not have a base adjustment. It appears the ECU controls the idle and compensates for engine wear.

My '89 244 idles fine when you first crank the car but seems to be a bit fast (1200 to 1400 rpm) when the engine warms up and the car is in park. I did a little swapping and ended up with a 571 ECU (940 16 valve) to use as a spare. When I received it yesterday I connected it to my car to make sure it was good before I commited it to the parts box in the trunk. I started the car and it ran great until the system went into open loop. As soon as it went into open loop the idle jumped up to just over 2000. I went and test drove the car and it seems to preform MUCH better than it did with the factory 556 but the idle never did settle down.

It was late and dark so I didn't check anything last night. What should I check first? I have replaced the Idle air motor but I guess it could be acting up. I don't think it's a vacuum leak but I do know that my check valve at the intake is not working just correctly. When I go up a long hill the vents switch off, kind of a sign that the valve is malfunctioning. I've wondered for a long time if the ECU temperature sensor was not functioning correctly. Could that sensor cause a fast idle issue? I have not changed the O2 sensor since I've had the car but Bentley says there is not set maintenance time on it from "89 up. What do you guys and gals think? The engine idles perfect while in closed loop and only seems to idle fast after entering open loop.

Thanks for your help,
Tony T
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Tony Turner 89 Volvo 240DL 257K, 92 Jeep Cherokee 250K, 93 Jeep Grand Cherokee 215K, 1980 Mercedes 240D 360K