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E34 (1989 - 1995)

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Old 02-20-2014, 05:05 PM
Frostycdn Frostycdn is offline
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Mein Auto: 1994 503I
530i with rough idle - I'm stumped.

After days of searching and reading thread upon thread I have tried almost everything and my idle remains the same.

Start the car and it idles fine for about 1 minute. Suddenly engine speed drops and engine compensates and revs up to about 1500 rpm and drops to about 700 rpm and it runs rough and engine light comes on.

Drive the car away and engine light turns off and car runs fine until I come to a stop and the process repeats itself. If the car is driven on the highway no engine light.

I have replaced idle speed sensor and mass air flow sensor. I checked the IAC valve and it's clean and the small valve door moves freely inside. I have checked all hoses and connections and sprayed ether around the manifold to see a if there are any leaks thus increasing the idle and nothing.

The stomp test does not work and I'm unable to retrieve the codes.

Can the IAC be faulty even though it's clean and moves freely?
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Old 02-21-2014, 03:40 PM
Doktor Bert's Avatar
Doktor Bert Doktor Bert is offline
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Location: Palm Springs
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Mein Auto: BMW 525i
I would suspect an ignition coil...
"Herr Doktor will see you now..."
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Old 02-22-2014, 08:15 AM
Frostycdn Frostycdn is offline
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Mein Auto: 1994 503I
Originally Posted by Doktor Bert View Post
I would suspect an ignition coil...
I disconnected the MAF and the car runs fine... It idles perfect. The check engine light is on steady now.

MAF is new.
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Old 02-22-2014, 09:53 AM
imae34driver imae34driver is offline
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Location: Orange County , CA
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Mein Auto: 1995 540i SPORT /6 spd
02 sensors?
Bone stock 95' 540i/6 Blk/blk w/ ram style C.A.I / JBR LWFW/ DUDMD tune/ straight pipe /545 SSK /3.15 LSD / Rev-shift motor mounts/stage 4, 6 puck clutch/ K Sport coil overs/Eibach sway bars/ VAC under drive pulleys/weight reduction /sparco 368, Recaro seats, sparco harnesses, NX wet kit, M/T E/T streets.

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Old 02-22-2014, 11:51 AM
Mamij Mamij is offline
Location: Denmark
Join Date: Apr 2007
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Mein Auto: BMW 320i M52 1996
This elegantly demonstrates the benefit of the disconnect test. For drivability problems, if error codes are either not forthcoming or helpful, the disconnect test will locate the problem fast. The drivability sensors are the maf, icv, ats, tps, the ects and the o2 sensor(s)

Quite obviously, the MAF is screwed even though its supposed to be new. Return it for a replacement.

The CEL will stay on while the maf is disconnected. You can drive the car safely this way. Your fuel economy won't be great. If its much worse than with the maf connected, connect the maf in until the new unit arrives.

With the maf, you can safely replace it with a good used unit as long as it is oem. Around $40-$50 shipped. The OP probably bought a cheap new no-brand maf from ebay for $80 (please confirm). They are not all that reliable. If thats what you bought, I suggest you return it for a refund and purchase a good used oem unit off ebay instead. Yup.
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Old 02-22-2014, 12:23 PM
Mr._Graybeard Mr._Graybeard is offline
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Mein Auto: '95 540i, '95 525it
Vacuum leak. Cracked intake boot, leaky intake gaskets, profile gaskets -- I'd check the intake boot closely first. If you have access to a Mytivac or other vacuum gauge you could either confirm or rule out a vacuum leak in a couple of minutes.
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