My 1988 740 GLE (non turbo) was stalling during cold starts a few seconds after starting. However once the car warmed up it ran great. So at the suggestion of this board I replaced the IAC valve. I went to start the car this morning for the first time with the new IAC and it immediately revved high (2500rpm) and stayed that way for about 5 minutes until warm and then settled down to about 1000rpm. The next time I started a few minutes later(when the engine was warm) the idle stayed at about 500rpm and after a few mintues of driving settled at around 1000rpm.

So it seems that the resting idle is all over the place with the new IAC. Is it possible that the ECU needs to adjust to the new IAC? Is it possible for the ECU to adjust/learn? Any suggestions?

Thanks

The ECU does not have to "get used to" a new IAC valve. The valve goes two ways: toward "open" and toward "closed." At idle, the ECU constantly makes it go back and forth between the two positions, giving it more "open" to raise the speed and more "closed" to lower it. It does not return any signal to the ECU. The ECU gets an RPM signal from the ignition circuit. In idle mode (when the throttle position switch is saying "idle") this input is used to set the idle speed.

Going back to the original problem, it seems that your car ran better before you changed the IAC valve.

Problems while cold can be caused by a bad temp sensor. There are two. The one just above the IAC valve is for the temp gage, and will not cause any running problems. There is another temp sensor under the last runner of the intake manifold, behind the breather assembly. It has a Bosch plug on it, as opposed to the one for the gauge, which has just a slide terminal. If it is bad or has a bad connection, it will cause temperature related running problems. Note the condition of the insulation on the wires to the sensor (and the IAC valve). These cars are notorious for rotten insulation wherever it is exposed outside the plastic sheath. I use liquid vinyl "electrical tape" when appopriate. You can re-insulate the wires without cutting and splicing.

Good luck!

Don't force it -- get a bigger hammer!

Checking further, I see I was thinking of an earlier edition. The newer ones (including '88) may have a combined temp sensor. I couldn't see the rear hole to see if it has a sensor in it.

Sorry...

Couple of thoughts.

When you replaced the IAC, any chance you bumped the connector to the ECT, temp sensor, that sits right behind it? Check that connection, and the wires to the connector for faults.

Did you remove the throttle body when you replaced the IAC? Is the wire connector for the TPS firmly seated? It should return a noticeable "click" when the wire bale seats. The IAC opens when the throttle positioning switch signals the ECU that the throttle plate is closed. There's an adjustment that has to be done if the TPS has been removed from the throttle body. See the 700 FAQs for details.

Good Luck.

Try disconnecting the throttle linkage. It may be too short and holding the throttle plate open slightly. The idle should not change when the linkage is reconnected. If it does then it's too short.

I will check out the throttle linkage, but am interested to know if the ECU is capable of adjusting to the new IAC?

I'm pretty sure your yr group does not have a "learning ECU".
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The throttle linkage checked out okay. Any other ideas as to why changing the IAC valve would cause the idle to be more erratic.

The obvious question is the "arrow" on the IAC pointing towards the engine block? Do you have the correct IAC part number?
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Thanks for the reply. The IAC arrow is pointing toward the block. I ordered the IAC (rebuilt) from FCP Groton. They assured me that it was the correct part for my car. I am not sure what to do next. I hope that over time the car will "adjust" to the new IAC. As it is now, the idle (when cold) is all over the place. High one time and low another. Whereas with the old IAC the car would stall a few times immediately after starting, but once started (usually the third time) the idle would quickly smooth out to 700rpm.

You can check the IAC operation by connecting 12 volts to the middle pin and grounding each outer pin one at a time. The valve should quickly flip back and forth. Have you checked the throttle position switch operation? Maybe an intake manifold leak that seals up better after things get warmed up?

Does it have a bosch part number on it?

The FAQs has testing procedures for the IAC. Also symtoms of dirty throttle body.
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It does not have a bosch part on it. The remanufacturer put their own metal stamp on it. I cleaned the throttle body before I got the new IAC. I will check the FAQs in order to test the IAC. - Thanks