E12 535i barely running

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ArtJohnson
Posts: 38
Joined: Thu Jan 06, 2011 1:29 pm
Location: Denver PA

E12 535i barely running

Post by ArtJohnson »

I've had this car for about 10 years and 30k trouble-free miles. I had a local shop rebuild the front calipers, they kept it for weeks and when I got it back, it barely runs. It starts when cold, idles rough and jerks and hesitates upon accelerating. The problem worsens as the motor warms up to the point where it won't run at all at its normal operating temperature. Along with that, the windshield wipers won't turn off once activated, and they replaced the 4-way flasher switch. They talked about having to charge the battery, and it seems to me that whatever they did at that point could be the cause of the electrical issues. I'm pretty much on my own with it now. I've had similar problems with AF sensors in Motronic BMW's, but I don't want to start with that because the euro sensor is rare and and about $800. The ECU can be repaired in the U.S. if necessary. Given that I can't just try another AF sensor or an ecu I'm not sure how to go about diagnosing this, and any suggestions are welcome.
Live Boldly.
1977 530i (72k), 1980 M535i, 1981 M535i, 1986 M5 Euro, 1988 535is,
1990 M3, 1991 M5, 1991 325iX, 1995 M3, 2007 Z4 M coupe, >40 other BMW's down the road
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Mike W.
Posts: 2653
Joined: Wed Aug 30, 2006 12:12 am
Location: Sonoma County

Re: E12 535i barely running

Post by Mike W. »

Do the basics. Start with a new coolant temp sensor, the one for the FI, not the gauge. Check timing, maybe replace Dist cap, rotor and spark plug cables, and check fuel pressure. No guaranty this will solve your problems, but it might.

Wipers not shutting off is likely a problem inside the wiper motor, remove, clean out the 40 year old grease and put in new grease that's less glue like. The 4 way flasher switch is a common problem which causes the 4 ways to come on and stay on, so having replaced it isn't suspicious.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
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maybeillbuyit
Posts: 322
Joined: Mon Feb 17, 2014 12:26 am
Location: Vancouver BC

Re: E12 535i barely running

Post by maybeillbuyit »

Maybe my ignorance but AF sensor? What is that? AFM? I would recommend investing in a spare ecu. That item is specific to your M90 and getting harder to source. I have a spare ecu for every BMW I own in the trunk. Wether thats the current problem or not, having one is gold. You could swap out the ecu and rule it out right away. Same with a spare AFM. Good used one of course.

This one I think. https://www.ebay.com/itm/154704327579?h ... Sw6KdhlEjv
1977 530i another project
1979 635csi Euro "project"
1987 635csi
ArtJohnson
Posts: 38
Joined: Thu Jan 06, 2011 1:29 pm
Location: Denver PA

Re: E12 535i barely running

Post by ArtJohnson »

I thought I'd update with progress on my barely running m535i in the event that it might be useful for someone else. I replaced the cap rotor and plugs and it was clear that the car was running too lean as the tips of all 6 plugs were white. I replaced the coolant temp sensor that feeds the ECU, and that didn't help. Fuel pressure was good, but I blew the lines, and replaced the fuel pump, filter and the fuel pressure regulator anyway (with new Bosch parts). Still no improvement. I didn't know where to go next, so I went into the air flow meter box. It has a spring loaded dial that is quite easy to adjust. I reduced the spring tension one notch at a time, and the car ran better and better. I left it on the 3rd notch, and when the motor warms up to running temperature, the car drives nearly perfectly. There is still some hesitation until the car is fully warmed up, and a hiccup or two when accelerating hard. I sure wish I could find the actual problem, but for now, under normal conditions, the car is very driveable. I also found out that the electrical problems were almost certainly cause by the car having been left out in a big rain with the driver's window open. In addition to the electrical problems noted previously, the 4-way flasher relay failed. When I took it apart, there was water in it. I know that seems pretty improbable, but there it was.
Live Boldly.
1977 530i (72k), 1980 M535i, 1981 M535i, 1986 M5 Euro, 1988 535is,
1990 M3, 1991 M5, 1991 325iX, 1995 M3, 2007 Z4 M coupe, >40 other BMW's down the road
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