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E28 (1982 - 1988)

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  #1  
Old 11-29-2011, 03:31 PM
mrbbchevy mrbbchevy is offline
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Location: NY
 
Join Date: Nov 2011
Posts: 4
Mein Auto: 528e
Post e28 hard cold start/runs rough over 1/4 throttle

I am trying to help a friend with a botched craigslist purchase. I am working on a 88 528e and scratchin my head at the moment. The problem:

the car runs rough at idle till it warms up to operating temp ... then it smooths out the idle. while warming up, it surges between 750 and 500 rpms sometimes stalling out. no missfire can be heard and I have checked for vacuum leaks, but the idle control motor is constantly moving. In addition, after warm up it has a lack of power at anything over 1/4 throttle. It starts bucking and misfiring violently. Under 1/4 throttle it will reach 4000,5000 rpms no problem. you can ramp the car up to speed by manualy shifting, but ther is still a lack of power. Coolant and air temp sensors tests good hot n cold(multimeter). new plugs....cleaned the cap/rotor that were arced and carboned. no misfires till over 1/4 throttle...fuel pressure regulator aqnd in tank pump replaced after having fuel pressure issues...good volume test and over 80 psi at the rail when the return from the regulator is pinched off. cleaned the airflow sensor with map sensor safe cleaner. couuld the cap n rotor still be the cause of my lack of power even know I can produce misfire free rpms at low load?
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  #2  
Old 11-29-2011, 04:28 PM
catso's Avatar
catso catso is offline
catso
Location: Chicago
 
Join Date: Dec 2009
Posts: 2,946
Mein Auto: 2000 323i, 1988 528e
Quote:
Originally Posted by mrbbchevy View Post
I am trying to help a friend with a botched craigslist purchase. I am working on a 88 528e and scratchin my head at the moment. The problem:

the car runs rough at idle till it warms up to operating temp ... then it smooths out the idle. while warming up, it surges between 750 and 500 rpms sometimes stalling out. no missfire can be heard and I have checked for vacuum leaks, but the idle control motor is constantly moving. In addition, after warm up it has a lack of power at anything over 1/4 throttle. It starts bucking and misfiring violently. Under 1/4 throttle it will reach 4000,5000 rpms no problem. you can ramp the car up to speed by manualy shifting, but ther is still a lack of power. Coolant and air temp sensors tests good hot n cold(multimeter). new plugs....cleaned the cap/rotor that were arced and carboned. no misfires till over 1/4 throttle...fuel pressure regulator aqnd in tank pump replaced after having fuel pressure issues...good volume test and over 80 psi at the rail when the return from the regulator is pinched off. cleaned the airflow sensor with map sensor safe cleaner. couuld the cap n rotor still be the cause of my lack of power even know I can produce misfire free rpms at low load?
I would certainly replace the cap and rotor, cleaning rarely works. Then thoroughly clean the idle air control valve and especially the passages connected to it. It may need to be replaced. There's also probably some kind of vacuum leak, maybe the valve cover, etc. Check or replace any and all of the rubber hoses, boots, etc.
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