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High Idle 1990 Regal Custom 3.1

I have been chasing a high idle problem and need some help! It began with a sag or hesitation problem, then after replacing the PCV valve and hose, it started having a high idle problem (Error Code 35). The idle will only come down after resetting the ECM by removing the fuse or battery cable. After relearning, it will run fine until the engine is turned off. Upon restarting, the idle goes high to around 2000 rpm and will not come down even when warm. If I remove the fuse and reset the ECM, the idle will come down on the next relearn. Scanning does not indicate any unusual or out of range sensors with one exception. I noticed the BLM is running high, on average 147-150. I do not know if this is related. The IAC steps (or position) is 100 after turning the key off/on. I think this is the normal parked position. The IAC valve appears to be functioning properly because when the ECM actually gives the IAC a command to lower, the position goes down to 10-20 after a relearn. I have replaced CTS, IAC, MAP, PCV valve & hose, upper intake plenum gaskets, vacuum hoses.

Reply to
regalcustom1990
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Reply to
Shep

Thank you for the suggestion. I checked and cleaned the idle control valve port and throttle body, No change. It appears that the IAC will move to the correct position when commanded by the ECM, however it appears the ECM does not give the correct command. For example, the desired idle indicated by the ECM (from the scanner) is 700 rpm but actual idle is above 1500 rpm. After restarting the engine, the command position will not go lower then position 50 (or steps) when it should be about 10 -20 steps. This results in an idle above 1500 rpm. I can't figure out what is causing the ECM to not lower, or "kickdown" the IAC to the normal idle position of 10-20 steps.

Reply to
regalcustom1990

Please quote the text you are responding to. It's very difficult to figure out what suggestion you're referencing when you don't post included text.

Reply to
Mike Marlow

UPDATE - Problem Solved

This one had me going for more then two months. In a fit of rage, I just started unplugging sensors one by one until something changed. Finally when I yanked the Coolant Level Sensor (CLS, the one in the radiator) the idle jumped up, then lowered to ~800. I knew I had found something. I reviewed the scanned data recorded during the test and noticed some funny things happening to the 5 volt reference supply from the ECM. I then disconnected the battery to reset the ECM - with the coolant level sensor disconnected, and reconnected the battery leaving the CLS unplugged. I restarted and let the ECM relearn and that solved the problem. It appears that the CLS was intermittently shorting and causing the ECM to go nuts. I hope the information can help someone else.

Reply to
regalcustom1990

Thanks for posting this. This is the kind of "good to know" stuff that fits well into the back pocket.

Reply to
Mike Marlow

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