Engine RPM Cycles Up and Down Under Load - BMW Forum

chachaE36 · 02-19-2010, 11:08 AM

I have a 95 325i Convertible with 91,000 miles. When driving under load the engine RPM cycles up and down about 2000 RPM. With very light throttle applied engine speed is constant and slowly increase with speed. Behaves like this at all speeds, hot or cold engine. This started all of a sudden about a month ago (didn't gradually get worse). No repairs have been attempted yet - any chance there is an easy fix to this?

marti5 · 02-19-2010, 11:26 AM

Sounds like the MAF/AFM to me, you can try giving it a clean with carb cleaner, or you may have a vacuumm leak check your intake hose for cracks or splits, but I reckon its the MAF/AFM playing up, unplug it and see what happens.....

#1 MAF and #3 intake hose, here:

http://www.realoem.com/bmw/showparts...=13&fg=15&hl=1

Ps. welcome to the mad house!!

chachaE36 · 02-20-2010, 03:33 PM

OK, I pulled the MAF and cleaned it very thoroughly following the example in this YouTube link:

YouTube - Kajza M3 E36 - DIY cleaning maf / mass airflow sensor m3 e36 bmw luftmassenmesser

The problem is 95% improved but I can still feel a very subtle surging of the engine when accelerating. I am going to drive it like this for a week and then clean it again. Thanks for the help

witeshark · 02-20-2010, 03:57 PM

Very cool!

97alpineM3 · 02-20-2010, 07:02 PM

Did that fix it? Sounds like it was probably dirty. There are not many more things that can cause the same problem.

Les

marti5 · 02-21-2010, 04:12 AM

If it keeps doing it after another clean it probably needs a AFM replacement.

darkhorse737 · 02-21-2010, 12:02 PM

1995... that's a 15 yr old car.

It's already been mentioned by marti, but carefully check the intake boot for cracks and leaks. bimmers of the 90's are notorious for these

chachaE36 · 03-04-2010, 05:50 PM

OK, I've cleaned the MAF 3 times and the problem is still there. Also, I borrowed a MAF from a friends car and mine drives the same. I looked carefully at the intake boot and there do not appear to be any cracks. Next, I guess I am going to change the intake hose and see if that fixes it. If anyone has any other suggestions let me know. Thanks