I'm putting finishing touches to a 4yr body restoration to a 320i 1989 convertible. 1/4 million miles, original M20 motor mostly untouched throughout, except for occasional 5 minute warm -up, each time cold idle briefly 1,000rpm down to 600-650.
Morning before new MOT idle now PULSING 1,200 to 2,000 rpm until warm then perfect at 650. MOT day idle STARTS at 1,500rpm, CLIMBS to 2,000 until warm, then 650 again.
Passed the MOT, (kept it warm) easy drive home then decided to clean the Idle Control Unit, click / clack rocking sound pretty free. Put the ICV back on, checked pipework for splits, listened for the ICV buzzing, started the motor. Instant revving to 3,000, climbed to 3,500 revs white smoke exhaust, panic, turned it off!
Got out the multi-meter to check ICV resistance, 38ohms across the outer ICV pins, 20 ohms one side, 18 the other. Checked the voltage coming through the 3pin connector, 9 volts centre pin to earth, 9 volts centre pin to one side, but ONLY 3.8 volts centre pin to the other side.
Question: could this imbalance cause the excessive revs, is this an ECU problem?
Question: where is it getting all this air from to maintain 3,500 revs ?
I have no idea if it will idle at 650rpm once it's warm I'm too chicken to try. Trevor Moore.
Crazy 3,500 rpm instant 'idle'.
Moderator: martauto