91 745, 160k. Always starts easily. When cold it idles about 700, always. When warm it usually idles at 1300, no irregularity, just a high idle. Sometimes it will idle at 700 when warm though.
When running all seems fine, no other signs of performance difficulty.
I both cleaned and changed the IAC, so there has been two different ones in there and one is from my old car that ran perfectly. The symptoms are the same with both of them. I've gone over the vacuum lines and see nothing, and have been over the FAQ.
Ideas? Thanks

Seems this Is related to the air conditioning being switched on. It isn't working, so apparently when it's on the brain expects a load that doesn't happen, so the idle goes up. Switched it off, idle stays at 700 or so.
Thanks for replies, good ideas which I'll look at also.

Sadly, my '91 745T does the same thing, but the other way around: cold idle is fine, warm idle is usually at about 650, where it belongs, but can sometimes go up to about 1300. In other words, it is more often than not idling properly, only occasionally goes up to 1300. Has driven me nuts for years.

Is your speedometer working? What error codes is your LH 2.4 fuel injection computer giving you? The only diagnostic code that I get consistently is the lack of data from the speedometer, or 3-1-1, because the speedo does not work. The FAQ does say that the 3-1-1 error code will cause "Idling problems," but since the problem is not consistent with my car, I don't think this is the cause.

One day, then the outside temperature is nice and comfortable, and I have the time and inclination, I'm going to go over every single sensor feeding data to the LH 2.4 computer. In other words, probably never, but . . . I think the problem may be caused by sensor drift in one or more of the 12 to 15 sensors that feed data to the computer.

Also, it may have to do with making sure the throttle body butterfly is properly set for idle operations. Not particularly difficult, but I can't figure out how to clamp off the little air hose feeding the IAC valve. Not without risking shorting vice-grips against the terminals on the back of the alternator.
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Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)

Pretty sure it's not the MAS, or AMM as some call it, I have a bunch of spares and those don't seem to make a difference. I'm going to check the codes; the speedo is Not working actually and it's been determined that it is the head and not the sender so I have another speedo coming. I'm going to spray around the intake etc and check the codes, have to do that in a couple of days. There are no deposits in the throttle body or the intake hose, using Chevron Delo does that whereas most other oils do leave deposits it seems.

One thread mentioned a situation where if the air isn't working but it is switched on, the brain thinks there will be a load that doesn't happen so the idle goes up. I'm going to check and see if the air was on when this happens.
I got the new relay and someone I know is going to solder it onto the controller board, I hope that will make the air work as it's great when it's operational.

Not sure if the 91's use a MAS but if so try cleaning it and also check that the air filter box thermostat is working properly and closing the heated air intake when it warms up.

I would spray some ether, carb cleaner, etc..around the intake manifold..If idle changes, suspect manifold gasket leak.
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Post Back. That's whats makes this forum work.

I would check your TPS sensor and the idle set screw.

Run the diagnostics mode test for your car and see if it responds to the TPS test. If not, the idle system (including the IAC) isn't even being activated. To test the IAC separately, apply 12V to it - If there are 3 pins, middle is ground. I may be thinking about the cruise control though.

Good Luck and post back,
Will
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1990 740 Turbo, on its way to stock specs, maybe beyond