Hey all
89 325i 5sp 120k
At cold starts I'll get a stumble and surging idle only when the car is entirely cold (sat more than 6hour say) and then only until I load it up some with some revs etc. For instance it'll happen while reversing in the driveway, pulling to the first stop then go away. So its not at all about the temperature of the motor. Nor is it really about exterior temp. Once it "clears its throat" it runs 10000000% perfect from idle to redline. Car was doing this before AND after a major rebuild which included the vast majority of culprits:
every single head and block seal/gasket replaced
valve adjustment
plugs, rotor, cap, throttle switch, 02 sensor, vacuum lines
fuel filter, fuel lines, fuel pressure regulator, fuel injectors cleaned with new seals.
My first thought was fuel pressure regulator since its responsible for keeping pressure 'overnight' but its a new name brand unit and behavior was unchanged before and after.
I gave the idle air valve a light cleaning, it move smoothly, cleaned elec contacts.
Not really sure what else....
Last edited by somecarguy; 05-14-2019 at 09:04 PM.
I did not clarify that when I first start the car on these cold mornings the idle is perfect at 800. It’s only when I open the throttle that the surging begins which to me suggests a rich or lean condition. This morning I did a test and let the car idle for two minutes before moving off. This resulted in almost no surging or stalling which leads me to believe this is a time based issue I am struggling to think which component needs two minutes or so to ‘wake up’. Surely there is not that significant an amount of heat added to the motor in that two minutes.
O2 sensor? Temp sensor to take car off fuel maps when warmed? No idea but just throwing stuff out
No e30s again.
Did the condition occur before you replaced the throttle switch? Have you tried adjusting the new one?
Yes and yes to throttle switch, adjusted per Bentley.
O2 and its heater relay a good candidate will look this wknd.
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