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7 Series - E38 (1995 - 2001)

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  #1  
Old 04-19-2014, 10:25 AM
Hdghawg Hdghawg is online now
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Intermittent loping at idle, no vacuum leak

First time poster to the forums but have been educating myself for several months, pretty much everything is in here but my head is spinning from information overload. I can't seem to find (or remember where I found) some of the information.

I have a 2001 740il, my reason for posting is that I'm still getting an intermittent loping during cold idle with "mixture control idle" codes for both banks (all misfire codes are gone now). Recently I replaced the the intake and valve cover gaskets, plugs, injector o-rings, CCV, and vacuum hoses. She runs great and fuel mileage is up but this idle issue remains. I have checked for vacuum leaks three times with a cold engine and nothing.

Could this be a bad MAF without a MAF code? I got one from the junk yard and soon got MAF and related codes (I guess that's why they're called "junk" yards), so I put the old one back. I also read posts about bad O2 sensors but no codes, another about a bad temp sensor, again with no code and something somewhere about the fuel filter. I don't mind spending the money on parts but I'd rather not all at once, would rather fix the problems first then gradually deal with maintenance things. She's got about 187,000 on her and I don't know if any of this stuff has ever been done.

I suppose the question is, can any or all of those things cause these codes, which one would you do first or am I missing something else altogether?
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  #2  
Old 04-20-2014, 09:49 AM
SFBayBimmer SFBayBimmer is offline
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Original O2 sensors with your 187k....you should at least consider changing your pre-cat O2 sensors. They can be slow to respond with age and mileage; they become lazy. They won't throw a code if they are at the envelope of the parameters, but they do get lazy. Now this might be unrelated to your current issues, but it wouldn't hurt IMHO.
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Last edited by SFBayBimmer; 04-20-2014 at 09:51 AM.
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  #3  
Old 04-20-2014, 11:29 AM
Hdghawg Hdghawg is online now
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Mein Auto: 01 740il, 02 530i
Quote:
Originally Posted by SFBayBimmer View Post
They can be slow to respond with age and mileage; they become lazy.
Hahaha, I can personally relate to that!

Looking through my manual I read where the pre-cat sensors monitor the secondary air system. Three days ago when the ses light popped on again besides the usual lean mixture codes I got codes relating to the secondary air system. Wouldn't it be nice if the o2 sensors were responsible for both codes and all I need is to change them out? (I'm skeptical since the codes are for both banks) I found Bosch MAFs for $99 and ordered one. I'm going to change the o2 sensors too. First MAF, wait a week for codes, then o2 sensors. If I do them at the same time I'll never know exactly what procedure fixed which problem.
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  #4  
Old 04-20-2014, 11:39 AM
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FABOCH FABOCH is offline
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My $$ is a MAF sensor going out....My 6 month old MAF sensor started to show its ugly head like so ...Why Do I go thru so many Sensors? My oil`d K&N filter....I have gone thru 4 already 100k miles driven....But once I get new MAF sensor the car purrs at cold start ups
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  #5  
Old 04-23-2014, 05:48 PM
Hdghawg Hdghawg is online now
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Got the new MAF this evening and put it on. Won't be able to tell if it fixes the "lean mixture" codes for a week or two as that's how long it usually takes to appear after I reset it. The cold idle loping I'll just have to wait and see also cause that only happens occasionally. I see how they sell this for $99 instead of $200 (or whatever), it's a vw maf sold to less knowledgeable BMW owners (that'd be me) as a bmw sensor. If I would've had this dang part number I could have ordered it as such for $72 instead of $99. For those that ever read this and want it it's a Bosch part #63136
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  #6  
Old 06-23-2014, 09:27 AM
injuhneer injuhneer is offline
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*bump*

I too have a mysterious misfire at idle. Engine was running great after new plugs and fluid service. One day it just started loping a bit intermittently at idle. It runns fine then just stumbles. No codes. No miss above idle.

No codes. Nada. Zip.

Voltages on all O2 sensors look good and responsive. Coils are all working. Fuel pressure is good. Injectors are working fine. MAF is clean and behaving. Position sensors are all working.

I am wondering about the idle control though. I have seen a problem on other cars (Porsches, Saabs and Land Rovers) that use a similar Bosch idle valve (with different plumbing). The commutator on the armature wears causing the idle valve to get "stuck" electrically. When it breaks loose and snaps close it causes a stumble in the idle.

I haven't cut this idle valve open yet to see if it is configured like all the other rotary idle air controls Bosch has made since the 1980's. If so I am thinking it may be the culprit. I have had success repairing the commutator on those valves and putting them back in service (salvaged a 924S valve to use in a 900 Turbo).

Or maybe the check valve at the brake booster? Maybe the booster is leaking a bit? I haven't found any obvious vacuum problems.

In any case any insight on code-less idle problems is appreciated.

-Mike O
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Last edited by injuhneer; 06-23-2014 at 09:29 AM.
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  #7  
Old 06-26-2014, 01:28 PM
injuhneer injuhneer is offline
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Any chance that worn timing chains could cause this?

I was checking various points on the car and noticed when it "misses" that it sounds almost like a mild backfire through the exhaust. A chuffing sort of sound.

-Mike O
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  #8  
Old 06-26-2014, 04:30 PM
tomloans tomloans is offline
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Check for oil in your spark plug wells

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  #9  
Old 06-29-2014, 07:38 AM
injuhneer injuhneer is offline
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Dry as a bone; recently installed new platinum plugs.

-Mike O
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Last edited by injuhneer; 06-29-2014 at 07:39 AM.
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  #10  
Old 07-01-2014, 09:19 PM
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BMWFatherFigure BMWFatherFigure is offline
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Clean the idle control unit fully first - cheap and two of mine got fixed like that. If you can test the unit electrically that would be good too. It is possible thet the movement is caused by a voltage less than 12v input so be careful. I am unsure of the actuating voltage - maybe measure on the car before you it test off.
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  #11  
Old 07-03-2014, 06:56 AM
injuhneer injuhneer is offline
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Quote:
Originally Posted by BMWFatherFigure View Post
Clean the idle control unit fully first - cheap and two of mine got fixed like that. If you can test the unit electrically that would be good too. It is possible thet the movement is caused by a voltage less than 12v input so be careful. I am unsure of the actuating voltage - maybe measure on the car before you it test off.
Thx. The ICV was cleaned when I first got the car because there was an ICV code. It now moves freely and buzzes a little (to the touch) when the engine is running.

These valves use a PWM signal to control position. The return spring inside holds the normal position (open) and the duty cycle of the signal (percentage of "on" time) moves the shutter. It can be measured with a good DMM that has a duty cycle function. I noted that the Bentley manual has no info on this. Is there somewhere in the BMW tools that the duty cycle of the ICV can be read?

The test basically involves putting the DMM probes on the ground and signal lines. The ECM pin assignments indicate signals for opening and closing windings. The meter will read the duty cycle on two lines so I guess these valves need to have each side checked separately. I suppose this will tell me if the engine management is abruptly adjusting the ICV.

-Mike O
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Last edited by injuhneer; 07-03-2014 at 07:38 AM.
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  #12  
Old 07-03-2014, 07:57 AM
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BMWFatherFigure BMWFatherFigure is offline
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If BMW's are the same as the rest of the auto world (I think in this case they are) the the basic duty cycle is 50% with hot engine and no systems on. The A/C and P/steering will up the idle speed and / or air flow. To a lesser extent the headlights will also up the idle. To adjust the DC %age the throttle stop will need to be tweeked. Make sure the idle valve and throttle body are both clean, very clean.
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  #13  
Old 07-03-2014, 08:01 AM
injuhneer injuhneer is offline
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Quote:
Originally Posted by BMWFatherFigure View Post
If BMW's are the same as the rest of the auto world (I think in this case they are) the the basic duty cycle is 50% with hot engine and no systems on. The A/C and P/steering will up the idle speed and / or air flow. To a lesser extent the headlights will also up the idle. To adjust the DC %age the throttle stop will need to be tweeked. Make sure the idle valve and throttle body are both clean, very clean.
Thx!

I was just looking at the throttle stop and TPS. The TPS does not appear to be adjustable (position) so I assume the value is internally referenced at startup.

Regards,

-Mike O
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  #14  
Old 07-03-2014, 05:50 PM
injuhneer injuhneer is offline
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Hooked the Fluke up to the ICV. After sorting which side was the opening vs closing coil the valve was running about 68% duty cycle. Rather than disrupt the stop for testing I made a few shims that saddle over the stop. A 0.020 shim put the duty cycle at 52%, 58% with AC and lights. The data logging was left running so it could be mapped (max/min). There was nothing dramatic happening before the idle stumble(s). Just after the OPEN DC went up to about 90% then back to ~50% quickly.

So, not the ICV or its circuit.

In this middle of all this, and just for grins, I unplugged the cam sensor. No immediate change in running but after about three minutes the engine started to stumble like the symptom. Plugged it back in and the stumble went away only to return in 3-4 minutes.

Ever onward.

-Mike O
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  #15  
Old 07-04-2014, 10:38 AM
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BMWFatherFigure BMWFatherFigure is offline
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Bad wire/connection/coil on the cam sensor?
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Previous:
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i
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  #16  
Old 07-08-2014, 09:25 AM
injuhneer injuhneer is offline
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Quote:
Originally Posted by BMWFatherFigure View Post
Bad wire/connection/coil on the cam sensor?
I suppose that is next. Assuming this is an active sensor like the others on the car what is the best method to check/test it?

-Mike O
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  #17  
Old 07-15-2014, 08:03 AM
injuhneer injuhneer is offline
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The quest continues.

I bought cam and crank sensors. The sensor I received for the cam is too long. Maybe for another model car? Rather than whinge about it I made a pair of spacers, one for the sensor body and one for the bolt, each 0.305" in length. Bolted it right up and plugged it in. Works like it should.

The idle misfire is not as frequent but is still there. No codes.

Cranks sensor is next.

I did notice though that when removing the coil/plug covers that wiggling the knock sensor wires seemed to cause a stumble. I am wondering now if the knock sensors are toast on one side.

-Mike O.
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  #18  
Old 07-15-2014, 02:13 PM
edognight edognight is offline
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I had a lope like a 70's camaro

On my car, it was a coil going bad intermittently. I changed everything you are supposed to change, MAF, intake gaskets, plugs, vacuum hoses, etc. $$$

Then a moment of clarity. I did the old fashioned cancellation, by pulling one coil wire at a time and number 6 made no difference at all. every other one made the car stumble something fierce, (because it was running on 6 cyl)

It was a bad coil, which only showed up as a misfire on the cly number on the computer. So I switched the coil to another cylinder, repeated the whole procedure, and isolated the coil as the culprit.

I am lousy at diagnosis, but the old cancellation is a tried and true method.
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Old 07-16-2014, 07:08 AM
injuhneer injuhneer is offline
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In this midst of this I did go through the connectors and clean them to verify. The engine acquired the same miss as each coil was disconnected in succession. None of the misses exhibited from a single coil was a severe as the problem being chased.

Multiple intermittent simultaneous coil failures? :-)

There was one added data point observed. The miss only occurs after the engine is warm. When cold it purrs.

-Mike O
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  #20  
Old 08-10-2014, 07:53 AM
injuhneer injuhneer is offline
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The battle goes on...

Crank and cam sensors have been replaced. Still no codes.

The behavior does not happen when the engine is cold. Once warm it will stumble (multiple cylinder misfire) as if the fuel or ignition were cut for a few tenth of a seconds. The stumble is not discernible over 2k rpm. Cruising on the highway from Tucson to my house on a long uphill grade the tach was just at 2k and I could feel the engine stumble. The duration felt similar to when it happens at idle. I though that the hesitation was transmission related but now know it can happen at any point.

So next I need to find what changes between cold and hot that enables the problem.
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  #21  
Old 08-10-2014, 08:41 AM
JasonSC540ia JasonSC540ia is offline
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I was getting kinda the same thing. Sometime rough idle, lopping. Missing and hesitation under load. Sometimes it would trip a misfire code but 90% of the time no code. I just fixed it Friday. Got my 8 new coils in and installed. Runs great. I did the same your doing. MAF, plugs CCV, vacuum lines. It all helped a little but didnt fix the problem.

Heres a link to my story. Hope it helps.

http://www.bimmerfest.com/forums/sho...d.php?t=785044
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  #22  
Old 08-10-2014, 09:35 AM
injuhneer injuhneer is offline
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Quote:
Originally Posted by JasonSC540ia View Post
I was getting kinda the same thing. Sometime rough idle, lopping. Missing and hesitation under load. Sometimes it would trip a misfire code but 90% of the time no code. I just fixed it Friday. Got my 8 new coils in and installed. Runs great. I did the same your doing. MAF, plugs CCV, vacuum lines. It all helped a little but didnt fix the problem.

Heres a link to my story. Hope it helps.

http://www.bimmerfest.com/forums/sho...d.php?t=785044
Thank you. I will read through this. At first glance it does sound very similar.

-Mike O.
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  #23  
Old 08-17-2014, 07:22 AM
Hdghawg Hdghawg is online now
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I thought I would post the fix to my problem.

But first,
Things got worse with the loping, you could rock yourself to sleep at a stop light. Was getting codes for random misfires and #5 cyl on start up. I tested several times with spraying around looking for vacuum leaks, even used ether, no luck. Finally had a smoke test done, #5 injector o-ring was leaking and the intake was leaking at the throttle housing (how in the world did ether not expose this I've got no idea, I tested these spots specifically). Anyway come to find out the o-rings I ordered on line were the wrong size, the gasket at the throttle housing was a goof on my part, I didn't replace it when I replaced all the others, lesson learned.....don't be so damn lazy.
So, I had the work done and she runs fine, which is really good since someone pulled out in front of my 528i and I'm waiting to get the official "it's totaled" next week......but that's for another forum.
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  #24  
Old 08-17-2014, 08:01 AM
JasonSC540ia JasonSC540ia is offline
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Glad to see you got it fixed.

I'm just curious, but when you performed your vacuum leak check did you use brake cleaner?

I asking because I see people mention to use brake cleaner on this site, but a lot of your modern brake cleaners are non-flammable and would not work a vacuum leak tester.

I use MAF cleaner. MAF cleaner still says "extremely flammable" on the side. Starting fluid is the best for testing vacuum leaks.

Just wondering

Cheers
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  #25  
Old 08-17-2014, 08:16 AM
Hdghawg Hdghawg is online now
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Quote:
Originally Posted by JasonSC540ia View Post
Glad to see you got it fixed.

I'm just curious, but when you performed your vacuum leak check did you use brake cleaner?

I asking because I see people mention to use brake cleaner on this site, but a lot of your modern brake cleaners are non-flammable and would not work a vacuum leak tester.

I use MAF cleaner. MAF cleaner still says "extremely flammable" on the side. Starting fluid is the best for testing vacuum leaks.

Just wondering

Cheers

The first thing I used was brake cleaner, then MAF cleaner, then something else I had on hand before I used ether. When the smoke test was done he did it through a vacuum port and nothing. Next he did it through the intake and that's when he found them.
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