# Idle surges a few times and then the engine dies!



## Beemaboy (Jun 1, 2006)

Hi Everyone

I hope someone can help me with a problem that my car has suddenly developed after coming back from a gearbox repair centre...
Car is a 1998 E38 (pre facelift) M62 740I

When I start the car, the revs instantly shoot up to 1500RPM and slowly, over about a minute, begin to fall back to about 1000RPM at which point they dip to about 200RPM, then the car seems to rev itself back to about 2000RPM, the slowly back to 1000RPM, then it drops to 200RPM and revs back to 2000RPM again...which repeats itself about 7 times before the engine seems to give up and then just dies...

I have found out the following...

Unplugging the MAF, car still runs and has the idle surge...
Unplugging the CPS, car still runs but splutters and still does the idle surge...
Checked engine with a finetooth comb and there are no vacuum leaks...
Unplugging the Idle Control Valve, car idles PERFECTLY at 900RPM and DOES NOT surge at all...

I have scanned the car for codes and nothing comes up...
I have also replaced the idle control valve with a working one and it made no difference...

Please, please someone help...
I have had to pay over $600 for the gearbox repair, and now the car throws this at me 

Thanks for any help :thumbup:

Rawdon


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## Beemaboy (Jun 1, 2006)

Can no one help


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## Payback (Jan 11, 2009)

Have you considered changing your fuel filter? This could be a cheap fix. Honestly, I would be looking for a bad sensor as the problem. Also check the throttle body (cables) located on top of the motor on the left side under the cover. They could be stuck in position. Then there is the possibility of it being a crank position sensor problem. I came across another posting on here with a similar problem. 

Good Luck


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## TerryY (Jul 20, 2003)

If disconnecting the idle control valve fixes it then there is a signal being sent to the ICV by the computer. Plug in the second ICV while holding it and see if it is opening and closing on command.

If it is then the transmission shop screwed one or more sensors up. 

All I can recall being in the region are the O2 sensors and the crank position sensor reads the flywheel on the M62. Plus of course the transmission wiring, but that shouldn't affect the idle.. O2 sensor connections would be a good place to start.


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## Payback (Jan 11, 2009)

I would trust TerryY and M.Wong opinions. I have read several of there replies to other posts and they appear to be very knowledgeable of these cars.


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## Beemaboy (Jun 1, 2006)

Thanks for the replies guys 

I changed my fuel filter not 2000miles ago, so hoping that is not the problem . I have also checked the throttle cables and nothing seems to be binding...the actual throttle moves smoothly right through its travel...
I am curious about the crank position sensor? I though that the car wont even start if the crank position sensor is shot? I have tried unplugging that sensor and starting the car, but the car just turns over 5 or 6 times and then cuts out and gives up trying to start...

I will check the O2 sensor wiring when I am under the car next... Is there any way to test the crank position sensor or should I just buy a new one? Would the camshaft position sensor have anything to do with this aswell? It is really annoying that no faults seem to be coming up 

I will plug in the other ICV and see what it is doing and report back...

Thanks again for all the help 

Rawdon


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## Beemaboy (Jun 1, 2006)

Sorry, forgot to mention aswell... If, while the car is doing this idle surging, if I put the car into D or R, the engine will stall out immediately, even though the revs are at about 1500RPM...

Rawdon


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## Beemaboy (Jun 1, 2006)

Just out if interest, can someone tell me what the car is supposed to do when you unplug the Idle Control Valve? Should the car idle at over 1000RPM, stall out and die??? It would help me to determine if it is an air leak or possibly a sensor?

Thanks
Rawdon


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## TerryY (Jul 20, 2003)

The ICV has a measured flow opening that should provide a set idle speed. When something like the A/C is turned on the extra load will slow the idle down so the electrical part of the ICV opens up more flow are to speed the idle back up.
During a cold start the engine up should have a faster idle which should be controlled by the signal to the ICV. 
A slow idle for any reason such as putting it in gear will be compensated by the computer thru the ICV. 

So if the ICV is not operational anything that increases the load could cause the engine to stall.


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## Beemaboy (Jun 1, 2006)

Hi TerryY

Just to report back on your suggestions...

I have checked the O2 sensor connections and 1 of them, if you can believe it, was only half plugged in!!! I removed both sensors and cleaned them, put them back in and tested the engine. Unfortunately, plugging that one in and cleaning them has made no difference...

I plugged in the idle control valve and observed the inside flap. When starting the car, the flap fully opened and then closed to about 50%. Then, over the next few minutes it moved slightly towards being 70% closed and then back to 50%...it never moved at all after that except when I revved the engine, which caused it to completely close. After revving the engine though, the engine stalled and the valve flap completely opened...

The car also seems to be slightly changing what is happening. When I first start it, it revs up to about 1500RPM and then in about 10 seconds, drops down to about 1100RPM. It starts to surge after about 1 minute and then starts to dip to 200-300RPM before revving back up to 2500RPM and then back down to 200-300RPM and so on...
It is as if something is activating after the warm up cycle and causing all this trouble...

Once again, still no error codes on the computer...

Anything else you can think of?

Many Thanks for all the help...

Rawdon


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## TerryY (Jul 20, 2003)

It sounds like the Idle control is responding to conditions as it should. 

Spark and fuel are next. What kind of sparkplugs are in the engine and how old are they? Bosch Platinum Plus plugs don't seem work well in the BMW V8 or V12.

When was the last time the fuel injectors had cleaner run thru them?

The computer seems to run the first step down of cold enrichment (like a choke) but it is failing to stabilize on the next stage. Nasty spark plugs or partially clogged injectors could do that.


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## Beemaboy (Jun 1, 2006)

Hi TerryY

Thank for the quick reply 

The plugs in the car are the normal 2 electrode NGK BKR6EK. I replaced them as part of a full service I did about 3 months ago...so they should be brand new...
I had the injectors cleaned about a year ago, at the same time that I did the PCV valve on the back of the manifold...

What are your thoughts on the Crank Position Sensor? Could one of these cause problems like this? I had a slight problem with the engine starting before I took the car in to the gearbox place...in that it would just crank for long periods before starting...and sometimes, I would have to try 3 or 4 times before the engine would catch and stay started...but, there was NO problem with the idling then...
Interestingly enough, a mechanic I took the car to about 4 months ago told me that the engine speed in the REV counter did not match what the engine was doing...

Rawdon


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## Beemaboy (Jun 1, 2006)

Bump...

Any thoughts on replacing the crank position sensor or am I barking up the wrong tree here?

Thanks
Rawdon


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## TerryY (Jul 20, 2003)

It is a possible cause and not all that expensive. Is the electrical connector tightly fastened?


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## Beemaboy (Jun 1, 2006)

TerryY said:


> It is a possible cause and not all that expensive. Is the electrical connector tightly fastened?


It is...I also cleaned it out with a liberal amount of electrical cleaner as both it and the sensor were covered in a lot of old oil...presumably from the old leaking tappet cover gaskets. Could oil have caused a failure?

Sort of running out of stuff to look at . Really hoping that it is the Crank Position Sensor...

Will go in tomorrow and pick one up from the dealers...
Here is hoping 

Thanks

Rawdon


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## Beemaboy (Jun 1, 2006)

Well...an update...

Replaced the Crank Position Sensor and NO change 

Decided to swop out the Throttle Position Sensor while I was at it and also NO change...

I have observed a few other things now though! If I rev the car and hold it at a fixed RPM (used a screw driver to jam the throttle open), the car will surge at this high RPM too. For example, holding the car at 2000RPM, the revs will start to fall to about 1800, then 1600, then 1450 and the car shudders and then revs itself back upto 3000RPM...the slowly settles back down to 2000RPM for about 5 seconds, then down to 1800, then 1600 and so on before shooting back up 3000RPM again, all without moving the throttle!!!
I am monitoring all this from Carsoft and during all these surges, the IDLE REGULATION tab under 'Live Data' tells me that the IDLE REGULATION is active, even at 2000RPM. Now previously, before all this trouble started, as soon as I touched the throttle, the ACTIVE would change to INACTIVE...

What would cause the car to also surge while it revving at higher RPM, not just idle?

So far, ruled out...
Mass AirFlow Sensor
Idle Control Valve
Crank Position Sensor
Throttle Position Sensor
Any Vacuum Leaks

Any other ideas? Does this sound like a computer issue...as in a failed DME?

Thanks so much

Rawdon


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## Beemaboy (Jun 1, 2006)

Guys...I think I may have found what the problem is!!!

I was staring at the engine, trying to think of something that could be wrong when I happened to look at the Fuel Pressure Regulator...
I thought about it for a while and decided to try running the engine with the vacuum line on the FPR disconnected. Well, to my suprise, the engine started cleanly and the revs settled at 1050RPM while cold. After about a minute, the revs slowly started moving to to about 700RPM and then down to about 650RPM upon which time the engine cut out...
I tried starting the engine again and the revs shot up to 1000RPM during start and then came back to 700RPM for about 30 seconds before they dipped down to 600RPM, followed by the engine dying.

I plugged the vacuum line back into the FPR and started the engine. Revs shot up to 1500RPM and the usual surging started again... So, I took a small hammer and tapped on the FPR and the engine started bucking and died! I restarted the engine and the revs went up to 1100RPM then came down to about 700RPM and the idle was stable for about 20 seconds before it went down to 600RPM and died again...

Could all this be caused by a faulty Fuel Pressure Regulator???

Thanks
Rawdon


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## TerryY (Jul 20, 2003)

Try putting a vacuum gauge in the line to the FPR. If it is fluctuating you need to find the cause. If it is steady the FPR needs to be changed.


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## Teacher92 (10 mo ago)

I know this is an old post but can anyone update me if that fixes the problem? I’m experiencing the same thing!


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## mmariak29 (8 mo ago)

I am also curious, as I am running into the same issue.


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