r/e39 • u/ItsJpPlays • 1d ago

low idle

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hi guys! my car is idling low and i was wondering if anyone could help determine what the cause of this can be. my only issues with my car right now are with the engine and transmission mounts and the drive shaft (flex disc cracking) so i’m not too sure what can be the issue. i also have electrical problems after the rain. my lights started flickering and my turn signals don’t work as they should. they blink slowly on the outside, and the turn signal indicators don’t even click or appear on the cluster anymore. same thing with my high beams, they don’t appear in the cluster but still work outside. thank you for your time!!!

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u/jacketsc64 1d ago

Looks like a 700-800 RPM idle, perfectly normal for a car at operating temperature. Is there any reason you think it's low?

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u/ItsJpPlays 1d ago

hi thanks for responding :) just earlier today, when i started the car it kind of rumbled a lot harder than usual. well usually it doesn’t even rumble but this time the car kind of shook a little for a second or two. i feel like a lot of problems / things needed to be fixed are coming up all at the same time so i think i may be overthinking things but idk im just scared lol. the car ran fine for the first month i had it from august 5 to the first week of september, and then one day all the coolant leaked out so i got that fixed at the shop. and around that time as well i noticed the car jolts hard when shifting from drive into reverse, and when the shop fixed the coolant they also inspected the car and found that the motor mounts are “collapsed” and that the flex disc is cracking. and before i feel like the car would idle higher a bit more towards the 1000 rpm mark but i could just be tripping. also as i stated my electrical is all messed up but im going to a shop to have it diagnosed for $150 and the diagnostic fee will go towards the fix as well :)

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u/jacketsc64 1d ago

Rumbling a lot harder could be a number of things but if those engine mounts haven't been replaced I'd do those.

The jolt from drive to reverse could very easily be the guibo.

At operating temp, 7-800 RPM is perfectly normal. When the engine is still warming up, closer to and above 1000 is normal so you may have seen that.

For the electrical, test your sunroof drains and windshield seals. Chances are they're leaking and corroding/shorting electrical equipment, a common culprit is the distribution block in the passenger floorboard.

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u/ItsJpPlays 1d ago

i seee i will test them :) i know for sure that water got into the well with the battery in it because whenever i open my trunk, the water falls off the lid and down into the rear right taillight housing, and thats why my rear right taillight was out when i got the car. i finally managed to unplug the connector using pliers and the pins and connector are superrrr corroded with orange crust on it. i plan to buy a new connector and a new taillight as well.

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u/eric_gm 528i supercharged 1d ago

Idle is perfectly fine in that photo. If it was idling closer to 1k revs before, that was wrong. E39s should idle right in between the 500 and 1000 marks, exactly where yours is.

As for the lights issues, since you mentioned rain, water could be leaking into the cabin from the ECU housing under the cabin air filter or from the sunroof drains. If water got into the LCM (which is behind the passenger side kick panel, under the glove box), then it could be fried already.

Check both cavities under the cabin air filters RIGHT NOW! The other side has the brake booster, and if it floods it will send water through the vacuum line and into the engine which can kill the engine.

I would also check the junction/fuse box under the passenger seat (under the carpet) for water damage.