350i RPM SURGING

[dukeenfield]

HI,After a short run,the motor begins to surge (rpm going up and down)and starts to loose tick/over altogether.It seems ok until I switch fan on and if I switch headlights on,it get even worse.Seems the more power that is being used,the worse the surging gets.I wondered if it could be bad connection some where,perhaps to ECU.I have checked the earth wires that fit onto the motor and they seem ok.Also I thought about disconnecting ECU,but not sure how plug unhinges.Has anybody had this problem before,or have you any idea's.

[digga951]

I had the exact same thing on my 350i not so long back. The rpm kept getting lower and lower over a period of time causing it to surge as the ecu tried to compensate. When the lights and fan are on, extra load is placed upon the alternator causing even more "strain" on the already dying engine, resulting in it cutting our altogether.

For me the remedy was simple - the big slotted idle screw on top of the plenum had become loose and was able to turn/undo itself over a period of time. I could set the rpm to about 800 in the morning, and by the afternoon the screw had turned slightly causing it to drop to around 300, and thus cut out. To fix, I simply removed it and wrapped some PTFE tape around the thread so that it couldn't move anymore. Has been fine ever since and all idle problems have vanished. May be something as simple as this on your car!

Dan.

[dukeenfield]

Hi,Thanks a will try that.

[gsx600]

Same happened on the 4?0, after I'd adjusted the throttle position to the recommened gap.

I just used thread lock on it and that seemed to cure it.