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Rickytickytavvy
11-10-2016, 10:06 PM
I have recently developed an issue with controlling the revs while under load in my 1987 635csi Automatic...

Car idles normally ( nothing new, I need to clean cold start valve so it idles a little low until it gets to temperature ), but as I give it gas the idle will suspend and lope when it reaches ~1000-1200 rpm. It happens in gear and in neutral/park - whenever it reaches that rpm level it will start "loping," like the motor's choking. It results in an almost complete power loss while in gear and goes to the brink of killing the motor, (but not quite) then spike back and drop again. Like a crappy roller coaster...

It doesn't seem like a misfire, but maybe an unmetered air issue. Still, I am going to check/replace the spark plugs and check the distributor cap.

The mechanism in the AFM moves smoothly, with no stopping or slowing when I move it manually. I'm going to check for leaks tomorrow as well when I have daylight to work in. I had a similar issue maintaining RPM when my idle control valve wiggled loose, but that was just struggling to keep idle speed and worked fine under load.


Any other ideas on what to check for? Any insight is greatly appreciated.

bkats
11-10-2016, 10:25 PM
Could be fuel pressure drop. Check the fpr, the filter, maybe the fuel pump.

Afm could have a worn or dirty spot on the track.

As far as air goes, I've only seen similar symptoms with a pretty big air leak. Not too many places a big vacuum leak could be.

Rickytickytavvy
11-10-2016, 10:36 PM
Could be fuel pressure drop. Check the fpr, the filter, maybe the fuel pump.

Afm could have a worn or dirty spot on the track.

As far as air goes, I've only seen similar symptoms with a pretty big air leak. Not too many places a big vacuum leak could be.

Thanks. I'll give those a look tomorrow.




Here is a video of what's actually happening.


https://www.youtube.com/watch?v=HmcXB_-sjm0