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7 Series - E38 (1995 - 2001)

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  #1  
Old 07-18-2012, 10:43 AM
Pcolravey Pcolravey is offline
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Location: Albany NY
 
Join Date: Jul 2012
Posts: 20
Mein Auto: 740i
01 740i - Idle problem

My 2001 740i has a idle & low throttle issue that has slowly progressed. The severity is variable, but almost always present.
At idle it seems to 'cough' or 'stumble'. = a few times, than a few seconds without the problem, then it stumbles again a few times. Under low acceleration it can be severe enough to make it feel like I shouldn't be driving it; often at a light I will put in neutral to reduce the sensation throughout the drivetrain. Under hard acceleration it seems pretty smooth.

No engine codes!

Done / replaced so far: air & fuel filter, checked by two different techs for vacuum leaks, MAF sensor, spark plugs (NGK), checked for fuel pressure, cleaned throttle valve. OSV changed 3 years ago as was one spark coil. Current mileage is 127k. Several techs have said 'wait for a code' but I really do not feel right driving it as misses.

It is scheduled for the $125/hour dealer this Monday, so if someone can help me prior to this I will be grateful.
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  #2  
Old 07-29-2012, 09:50 PM
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bluebee bluebee is offline
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Location: San Jose, California
 
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Posts: 21,283
Mein Auto: 02 BMW 525i M54 auto 130K
Quote:
Originally Posted by Pcolravey View Post
it can be severe enough to make it feel like I shouldn't be driving it;
I can't imagine that not throwing codes ... but assuming it's a misfire ... look here ...

- How to diagnose a typical BMW engine misfire (1) or a sporadic-temperature-change cold-engine intermittent misfire (1) (2)
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Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #3  
Old 07-30-2012, 06:51 AM
ou18 ou18 is offline
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Location: Boca Raton FL
 
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Mein Auto: 1997 740 IL
I had something extremely similar, where at lights it would stumble and want to die. To the point i had to keep my foot on the accelerator in order to maintain high enuff rpms to keep the car from stalling... As rediculous as it sounds. And I know you had two techs "Check" for leaks. My problem was so simple it made me angry i didn't notice it earlier. And Im not saying this is your problem, but give it a look see. Sometimes the simplest problems elude even the best of techs because they are looking for a big problem when it doesnt exist...

Bare with me while i try to explain... The plumbing from your air box thru the MAF tube to the accordion style tube. Just passed that on the top is a L shaped tube attached to it. Mine had separated on a side that was not easily noticeable.. Which was allowing unmetered air to flow into the intake because it was passed the MAF. This caused an extreme problem for the car while idling...

My fix, albeit probably not what everyone would do. I bought some black gasket sealer and sealed all around the edge of the connection point. Let it dry and put it back together. All my hesitation was gone, no more rough idle no more needing to hold my foot on the accelerator at lights, no more rough acceleration. Cost me 4 bucks for the black goop and a little time of waiting for drying...

Give it a look see, you never know what you might find.. By the way, as strange as it was, i had no codes on my dash either... Im not sure if the design of the air box plumbing to the intake changed between 97 and 2001, but its worth a 5 minute inspection...
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  #4  
Old 07-31-2012, 10:41 AM
ProudBimmerMan ProudBimmerMan is offline
ProudBimmerMan
Location: California
 
Join Date: Jul 2012
Posts: 2
Mein Auto: 1999 740i
I just purchased my son a 1999 740i. It ran great for a few weeks then we started having idle problems. Then it went away on its own. Then my son calls me and says that the car is idling rough again and has no power when you go to give it gas. I happened to ask him what he last did before the problem occurred and he said he was gassing the car up. So, I narrowed it down to the gas cap. The car still had the original gas cap. I drove down to where my son was and took the gas cap off and inspected it. It looked okay to my eyes so I put it back on carefully lining everything up. When I started the car the check engine light went off and the car ran great. I thought the problem was solved and I told my son to be very careful when putting the gas cap on and make sure to line it up so it seals properly. Two weeks went by and the same idling problem happened again. I asked him if he gassed up again and he said no. Now I'm baffled? I drove down to where he was at and checked the gas cap again and it seemed that it was on very tight and in an obscure alignment. This time I went straight to the auto parts store and purchased a new gas cap. I went with the more expensive locking gas cap even though the door automatically locks. I put the new cap on which didn't line up good at all but after 5 minutes I got it on. Upon starting the car it still had major idling problems and no power when giving it gas. I drove back down to the store and exchanged the more expensive gas cap for the cheaper one ($4.98). The cheap gas cap went on tight and sealed very nicely. I started up the car and it idled rough for 10 seconds and then after it worked the air out it runs great. The engine failsafe mode light turned off. I recommend to any other people having BMW engine idle, rough idle, no power and failsafe mode lights coming on and off or can't seem to narrow the problem down, then try a $5.00 fix first, the gas cap. Good luck!
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  #5  
Old 07-31-2012, 10:51 AM
ou18 ou18 is offline
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When the CEL light was on, did you read the codes from it?
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  #6  
Old 07-31-2012, 11:09 AM
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bluebee bluebee is offline
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Location: San Jose, California
 
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Mein Auto: 02 BMW 525i M54 auto 130K
Quote:
Originally Posted by ou18 View Post
i had to keep my foot on the accelerator in order to maintain high enuff rpms to keep the car from stalling
Bear in mind that, after something like 200 revolutions of misfire, the fuel will be shut off "permanently" to the cylinder (permanently being defined as until the next ignition start).

So, one trivial test to run when it stumbles badly is to pull over, turn the engine off, (some people say to wait 30 seconds), and then turn the engine back on.

Often that temporarily fixes the fuel-shutoff-related stumble - but - of course - the misfire cause is still there.

Ask me how I know:
- How to diagnose a BMW cold-engine intermittent misfire (1)

Quote:
Originally Posted by ou18 View Post
My problem was so simple it made me angry i didn't notice it earlier.
I had a similar misfire for about a year, which turned out to be just as ridiculously simple.
- Does the order of the misfire OBDII DTCs diagnostic trouble codes actually matter (1)

Quote:
Originally Posted by ProudBimmerMan View Post
we started having idle problems. Then it went away on its own.
Idle problems will never go away for long.

Most of the time, you have a vacuum leak or unmetered air making its way into the intake.

Your son's car is old enough to replace ALL the rubber hoses. We've identified all of them for the E39 ... most may be similar for your 740i:
- How to locate all problematic (between 1/8" & 9/32" ID) 3.5x1.8mm, 3.3x1.8mm & (between 17/64" & 9/32" ID) 7mm ID vacuum tubing (single material), vacuum hoses (multiple material), 3.3mm OD curved vacuum pipes (rigid tubes), 3.5mm & 7mm ID vacuum endcaps (closed end) & 7x3mm manifold o-rings (1) & 7.52X3.52mm and 9.2X2.8mm fuel injection o-rings (1) & gaskets (1) on the M54 engine & where in the USA to get new vacuum tubing & vacuum caps (1) & what SAE sizes to get for all the metric M54 engine vacuum tubes, hoses, pipes, and caps (1) & correcting the F-connector errors in the realoem diagrams (1) & finding the ends of hard-to-locate vacuum tubes (1) & sorely needed clarification on how the M54 CCV vacuum port works on the M52 CCV valve connection to the fuel pressure regulator connection (1) & how to make, borrow, or buy lean-condition misfire test tools to test for vacuum leaks & lean conditions (1) (2)

Quote:
Originally Posted by ProudBimmerMan View Post
Then my son calls me and says that the car is idling rough again and has no power when you go to give it gas.
Probably the fuel shut off 'permanently' (as I already explained above).

You really can not diagnose this properly (otherwise, you're just guessing) without doing a scan.

You happen to live in the only continental state where it's illegal to get a free scan at Autozone:
- Which states make OBDII scanning illegal by the auto parts store? Why?

So you need to invest in the $25 code reader:
- Cheapest CAN OBDII scanner on the net that reads DTCs, pending codes, & clears codes

Or, if you're technically competent, you can download & install the free tools (same tools the dealer uses):
- INPA, EDIABAS, NCS Expert, DIS, EasyDIS, Progman, & other BMW factory & dealer programming, coding, and diagnostic software (1) (2) (3) (4) (5) (6) (7) (8) (9) & related BMW diagnostic tools forums (1) (2) (3) (4) (5) & the most often recommended BMW diagnostic tools & cable interfaces (1)

Quote:
Originally Posted by ProudBimmerMan View Post
So, I narrowed it down to the gas cap.
Absolutely nothing you've stated 'narrows' it down to the gas cap, IMHO.

In fact, I removed my gas cap for six months as a test for the E39 team, and the lack of a gas cap didn't cause any stumbling at all.
- Experimental results removing the fuel filler cap (aka gas cap) on the BMW E39 with resulting OBDII DTC fault and drive cycle reset (1) (2)

Quote:
Originally Posted by ProudBimmerMan View Post
Two weeks went by and the same idling problem happened again.
I'm not surprised. You need to perform some simple diagnostics ... none of which you've stated you've performed.

Quote:
Originally Posted by ProudBimmerMan View Post
Now I'm baffled?
You have no data.

I'd suggest you run a $30 smoke test in addition to getting the $25 code reader.
- How to make your own smoke machine (1)

Quote:
Originally Posted by ProudBimmerMan View Post
Upon starting the car it still had major idling problems and no power when giving it gas.
By now you should realize it can't be the gas cap - it never could be - and it's wasting your time even looking at the gas cap. Personally I'd put the original gas cap back on, buy the $25 code reader, & then run the $30 smoke test.

If the DTC scan indicates a fuel starvation, then you can get the free autozone test kit for the fuel system:
- How your fuel injectors work (1) & reading fuel injection codes via the 'stomp test' (1) & how to replace and service a BMW E39 fuel injector (1) & replacing the 7.52X3.52mm and 9.2X2.8mm fuel injector o-rings (1) & home-made tools for fuel injection cleaning (1) & the most often recommended fuel system service outfits (1) (2) (3) & the location of the K96 fuel pump relay (1) & the location of the fuel system pressure test Schrader valve for the I6 (1) & V8 (1) (2) (3)

Quote:
Originally Posted by ProudBimmerMan View Post
I drove back down to the store and exchanged the more expensive gas cap for the cheaper one ($4.98).
Put the original gas cap back on the bimmer.

Quote:
Originally Posted by ProudBimmerMan View Post
The engine failsafe mode light turned off.
The failsafe could have easily been a P0455 or a P0442, neither of which would have affected your idle.
Quote:
Originally Posted by ProudBimmerMan View Post
I
recommend to any other people having BMW engine idle, rough idle, no power and failsafe mode lights coming on and off or can't seem to narrow the problem down, then try a $5.00 fix first, the gas cap. Good luck!
Well, I guess YMMV; but as I said, I removed my gas cap for six months, and that didn't cause a single idle or drivability problem.

But maybe the 740i is different?

Easy enough to test:
a) Someone with a 740i, please remove your gas cap, and drive for a day or three.
b) Let us know what happens.
__________________
Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need

Last edited by bluebee; 07-31-2012 at 11:14 AM.
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  #7  
Old 07-31-2012, 03:47 PM
ProudBimmerMan ProudBimmerMan is offline
ProudBimmerMan
Location: California
 
Join Date: Jul 2012
Posts: 2
Mein Auto: 1999 740i
Thank you Bluebee

Bluebee you are 100% correct. First of all I apologize to those that I just gave guessing advice to. I took Bluebee's advice and went and took the gas cap off and started the car and it ran just fine without the cap. I assumed it was the gas cap because the car ran terrible when I had the old cap on and then when I put the new one on it ran just fine. What are the odds of that happening? Now I'm worried it will die on my son again so it is permanently parked. In the meantime I ordered a OBDII code reader that can handle DTC's and resets. As soon as I get it I will do a scan and post my data. In the meantime while waiting for my code reader I am going to concentrate on replacing the vacuum tubes. Thanks for the advice!
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  #8  
Old 08-06-2012, 03:13 PM
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BMWFatherFigure BMWFatherFigure is offline
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Location: Perth, Western Australia
 
Join Date: Aug 2012
Posts: 2,345
Mein Auto: E23;E30;E38;E32;E34 +
Here is one that did work - the engine temp sensor for the efi (not dash gauge) goes out of calibration due to age and causes an overfuel situation. Install a 8k ohm resistor in parallel with the sensor and the EMU will under fuel the engine (thinking it is a little hotter than it actually is). Checking for vacuum tube leaks is well worth while as they crack/leak with age and under bonnet (hood) heat.
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