Bimmerfest - BMW Forums - View Single Post - RPM dip and dive
View Single Post
Old 12-29-2012, 05:11 PM
MP3_E46's Avatar
MP3_E46 MP3_E46 is offline
Code/wrench Monkey
Location: South Denver
Join Date: Oct 2003
Posts: 1,128
Mein Auto: Carefully
Originally Posted by bluskye View Post
I've had issues with faulty IBS (Intelligent Battery Sensor) and low battery in the past, both very bizarre.

IBS failure: RPMs would drop dramatically during cruising as if the car lost electrical. Codes would read faulty Water Pump and IBS in this condition. The faulty water pump code was triggered because it lost electrical power (electric pump). Dealer replaced IBS and all is resolved.

Low battery - the bastard issue to nail down: Subtle rpm dips at idle/cold. HVAC fan would go in and out in really cold or really hot conditions. Yes, HVAC fan. I replaced fan/resistor thinking they were busted, but that was not the problem. Resolved with a new battery, in my case, Interstate Megatron Plus. These issues were resolved by mistake as I normally swap out batteries every 5 years or so I dont get stuck out in the cold.

These cars are dam sensitive to electrical glitches.
Ouch, your pain is felt!

So the conclusion is if your battery is at least three years old and these symptoms appear swap the battery out first. Cheap-ish easy DIY (~$100 from Walmart) that would need doing sooner or later anyway

Six Euro Deliveries since December 1998 (Owned E46, E90, E91, E92 and E93)

28 vehicles in 26 years of driving so far. Guess I like cars
Reply With Quote