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Gentlemen,
Paul here, mid-Wisconsin small town 1990 745T 202,000 miles. Automatic.
There is consistent high idle when the motor is warm. That is 1600 rpm in neutral or park and somewhat less in gear.
There is no hard starting or stalling when cold. In other words, nothing else is wrong with the motor. It is starting great, just like it used to, and running strong on top of that.
However, Onboard Diagnostic says 3--3-2 when I am looking at test 2 in hole No. 2. not only when I have just barely turned the throttle spool but also when I have turned that spool as far as it will go. I do not get the expected 3-3-3 at full throttle. But the car is running fine, including during acceleration out on the highway. It just has that high idle as soon as the engine is warm.
I have cleaned recently inside the throttle body with throttle body cleaner, carb and fuel injector cleaner and break cleaner, in turn, using a grout brush to scrub crud off the inside wall of the throttle body. This did not solve the high idle when warm.
OBD says the idle air control valve is working fine and I can also hear it working and, when I pinch off the half-inch hose leading from the big three inch intercooler to throttle body hose down to the IAC, the engine slows way down and then stops. So I figure that air is not getting into the intake manifold through the throttle body past the butterfly at idle. Does that make sense? Is surprising to me that enough air can be drawn through the IAC to run the engine at 1600 rpm!
But what could be causing this high idle when the engine is warm? Maybe I should change the vacuum hoses? They all seem OK. The dashboard temperature gauge has not been working for months. I used to wash the engine frequently. Maybe the temperature senders are corroded? Maybe the computer never gets the signal that the engine is warm and so keeps a lot of gas going into the engine?
An aside here: I recently had the local radiator shop braze new tubes onto the lid of the in-tank fuel pump assembly. I also painted rustoleum onto the lid before reassembly. Now gasoline is no longer leaking out from the fuel system under pressure and there is no gasoline smell coming from the car anymore either. I got that idea of letting a radiator shop fix the in-tank assembly from the FAQ or the Forum, one of the two. Worked like a charm. Thank you.
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