High idle

[Jonty]

Hi all bit of an update. I’ve smoke tested and again found no leaks. I’ve taken the horns off and check the decel springs and they are fine but still have a 900 - 1000 idle (no hunting). Interesting I pulled the ICV cable off and the engine lowered rpm to about 700 and when I plugged the idle valve back in it shot up to 1000 again with a whoosh of air through the valve. This tells me that when I disconnect the idle valve it seems to close and idle is low. This means the ICV has enough range to bring the idle to 750 so why would it increase idle when plugged in? Is there a chance it is getting a faulty signal (maybe rpm signal to ECU?).

[Bitsyncmaster]

Hi all bit of an update. I’ve smoke tested and again found no leaks. I’ve taken the horns off and check the decel springs and they are fine but still have a 900 - 1000 idle (no hunting). Interesting I pulled the ICV cable off and the engine lowered rpm to about 700 and when I plugged the idle valve back in it shot up to 1000 again with a whoosh of air through the valve. This tells me that when I disconnect the idle valve it seems to close and idle is low. This means the ICV has enough range to bring the idle to 750 so why would it increase idle when plugged in? Is there a chance it is getting a faulty signal (maybe rpm signal to ECU?).

The idle ECU does monitor the RPM via the ignition pulses from the ignition ECU. It's strange pulling the idle motor connector changed the RPM since it should have held the same position as when it was powered. Did you try that test a few times? Maybe pulling the connector slowly at an angle did drive it closed.

I've never heard of a stock idle ECU not running the correct 775 idle RPM when the idle motor is not at it's maximum closed position. But to note, the stock ECU does not fully close the idle motor.

[Jonty]

The idle ECU does monitor the RPM via the ignition pulses from the ignition ECU. It's strange pulling the idle motor connector changed the RPM since it should have held the same position as when it was powered. Did you try that test a few times? Maybe pulling the connector slowly at an angle did drive it closed.

I've never heard of a stock idle ECU not running the correct 775 idle RPM when the idle motor is not at it's maximum closed position. But to note, the stock ECU does not fully close the idle motor.

Thanks Dave

Yes it’s very weird. When the engine was cold then pulling the plug off the ICM did nothing but as it warmed up then pulling the plug off dropped the rpm substantially. My idle has been perfect for years and the only change was a mech removing the manifold to replace a water pump. I was convinced he must have left a vac leak but the smoke tests are all fine. I’m at a loss as to what may have happened. I have your RPM module so that is fine and the idle motor seems to be functional. The mech did say he reset the timing at 14 degrees which is 1 degree higher but I wonder if something has happpened with the rpm sensor in the dizzy?

[Bitsyncmaster]

Thanks Dave

Yes it’s very weird. When the engine was cold then pulling the plug off the ICM did nothing but as it warmed up then pulling the plug off dropped the rpm substantially. My idle has been perfect for years and the only change was a mech removing the manifold to replace a water pump. I was convinced he must have left a vac leak but the smoke tests are all fine. I’m at a loss as to what may have happened. I have your RPM module so that is fine and the idle motor seems to be functional. The mech did say he reset the timing at 14 degrees which is 1 degree higher but I wonder if something has happpened with the rpm sensor in the dizzy?

I guess what I would do is try another idle ECU. I guess something could go wrong with the calibration but have never heard of it before.