E70 35d - Rough Idle & Misfire - SOLVED!

[Algold415]

UPDATE:

Finally got all the parts in last week. I was able to clean the carbon deposits off around the openings (manifold and valve cover). I didn't do a very thorough job since I knew that it's very likely that I will have to take the manifold off again. I reused the old gaskets for the time being since they didn't look that bad.

Next I installed a new fuel filter as suggested. The old filter definitely contained very fine particles as the diesel was drained, so thanks for the tip.

After inspecting and testing the injectors (as discussed earlier), I didnt see a reason to swap them for now. I decided to just put it all back together over the weekend, hope for the best and see how the car runs.

After starting the car, the same exact symptoms were present. I went to a gas station, filled a full tank of diesel along with an injector cleaner. I test drove the car over the weekend, using roughly a quarter of the tank. There doesn't seem to be any improvement or change in the rough idle, however, since I had more time with the car, I got a better understanding of how it performs.

To describe it best, it almost seems like a big vacuum leak (or a faulty injector not vaporizing fuel correctly). As I throttle up lightly, going up to 2500 rpms the engine shakes and skips. As soon as I press the throttle harder, and the turbos boost more, the engine seems to come alive and operates normally. This is especially noticeable at higher rpms, you can even feel a point when it sort of kicks in and runs good (around 2500-3000 mark with good throttle). So if the engine runs good at higher rpms/throttle, I feel like this is some kind of Air-fuel-vacuum issue.

Did anybody ever encountered a similar issue? My next step to diagnose was to do a vacuum leak down test but then i realised that the EGR is there (connected to the throttle body), and will probably leak air at the EGR cooler metal connector? Also, the EGR valve has some carbon buildup, can that cause a bad idle, is there a way to test the EGR valve?

Thanks in advance!

[MillerMav]

So you're saying that power doesn't really come on until 2500-3000rpm? If so, replace your MAP sensor. It's cheap and it takes about 15 minutes to swap them out. I'm willing to bet that's it. I had the same issue on my 2009 and looked at everything, ended up being a cheap, easy, MAP sensor.

[josiahg52]

I'd consider the boost pressure sensor, charge air temperature sensor and the MAFS. I had codes associated with some of these sensors but it ran terribly to the point that it eventually went into limp mode constantly with a few misfire codes. I believe my problem started with an EGR cooler issue. Or it's just old and I've put a lot of miles on it. I'm not saying throw parts at it, but take a look at them. I agree about the MAPS although mine looked great and still seems to be functioning.

[MillerMav]

Originally Posted by josiahg52

I'd consider the boost pressure sensor, charge air temperature sensor and the MAFS. I had codes associated with some of these sensors but it ran terribly to the point that it eventually went into limp mode constantly with a few misfire codes. I believe my problem started with an EGR cooler issue. Or it's just old and I've put a lot of miles on it. I'm not saying throw parts at it, but take a look at them. I agree about the MAPS although mine looked great and still seems to be functioning.

The way we discovered mine was Matt W. came over to my place with his 335d and we plugged in Carly's and compared data during idle. As soon as we looked pressure readings it stood out like a sore thumb. Ordered a new one and a few days later I was running good as new.

Also, it's not old and doesn't have too many miles. My 2009 had 220+k miles on it still ran great when I got rid of it. New owner has another 5k on it already and its still running strong. That engine is capable of 300k+ no problem if well maintained.

[Algold415]

Thanks for the suggestions, will do some more research and plan to diagnose/change the sensors. I might even swap them from my running X5 35d tonight and see if that has any effect. Thanks all!

[Algold415]

I swapped the sensors after work. The results were quite surprising... The MAP in the poorly running X5 was gummed up and barely had an opening in the tube. The MAP sensor that I swapped from a running X5 seemed to be in better shape and definitely had an effect on the idle once swapped in. When the engine started up, it was shaking and idling just like before. I let it warm up and took it out for a drive.

After about 15 minutes, the shaking was considerably less and even started to only happen under about 1500-2000 rpms. It was definitely running much much smoother, but not completely gone. It almost felt like the throttle flap is closed until ~2000 rpms and it's 'choking' the engine and then it suddently flips open and the engine pulls normally after passing that 2000 rpms mark.

I got back into the drive way and decided to check the grommet for the MAP. To my surprise, the grommet had a crack. I'm not sure if that made much difference but I decided to park my good running X5 for a few days and use its MAP+grommet to troubleshoot with. In the process of removing the good grommet, it fell apart (looks like it was quite brittle as well or perhaps I pulled it too hard).

I ordered a brand new MAP sensor+2 new grommets which should be here in a day or two. Hopefully this will solve the issue, I will update the post once I get the parts in and installed.

By the way, does the new MAP sensor need to be coded after it is installed? Thanks!

[robnitro]

No coding needed.

[josiahg52]

Incidentally, the "throttle flap" is usually open 94 to 99% during operation. Glad you're making progress on your diesel.

[Algold415]

UPDATE:

Installed the new MAP sensor today. Started the car and right away could feel that it's idling way smoother, the shaking is much less noticeable but still present.. I figured the computer needs to adjust to the new sensor, so drove it for about 15 miles through the blocks. Here's what I noticed:

1. From a complete stop I floor the throttle, engine doesnt react but slowly climbs(studdering) until just past 2000rpms. Then there's an audible 'click' from an engine bay, almost like a metal flap was suddenly opened or closed. As soon as the 'click' happens, the car takes off like it should normally if you were to floor the gas pedal.

2. If I start the car, pressing the brake with my left foot and holding it, try to rev the engine with my right foot, the revs slowly climb until 2000 rpms, then past seems to rev up normally.

Seems like some kind of vacuum/airflow issue. I'm thinking this has something to do with the EGR valve or throttle body. Are there any other places a 'click' can occur that would increase/decrease airflow?

Originally Posted by josiahg52

I'd consider the boost pressure sensor, charge air temperature sensor and the MAFS. I had codes associated with some of these sensors but it ran terribly to the point that it eventually went into limp mode constantly with a few misfire codes. I believe my problem started with an EGR cooler issue. Or it's just old and I've put a lot of miles on it. I'm not saying throw parts at it, but take a look at them. I agree about the MAPS although mine looked great and still seems to be functioning.

Josiah, is the boost pressure sensor same as MAP sensor?

Thanks guys!

[josiahg52]

Originally Posted by Algold415

UPDATE:

Installed the new MAP sensor today. Started the car and right away could feel that it's idling way smoother, the shaking is much less noticeable but still present.. I figured the computer needs to adjust to the new sensor, so drove it for about 15 miles through the blocks. Here's what I noticed:

1. From a complete stop I floor the throttle, engine doesnt react but slowly climbs(studdering) until just past 2000rpms. Then there's an audible 'click' from an engine bay, almost like a metal flap was suddenly opened or closed. As soon as the 'click' happens, the car takes off like it should normally if you were to floor the gas pedal.

2. If I start the car, pressing the brake with my left foot and holding it, try to rev the engine with my right foot, the revs slowly climb until 2000 rpms, then past seems to rev up normally.

Seems like some kind of vacuum/airflow issue. I'm thinking this has something to do with the EGR valve or throttle body. Are there any other places a 'click' can occur that would increase/decrease airflow?



Josiah, is the boost pressure sensor same as MAP sensor?

Thanks guys!

From what I understand, no. This is because the manifold pressure can vary independently depending on the turbo waste gate position. Speaking of which, maybe that's the click you hear? You may have a vacuum issue. Or an intake hose problem.