Throttle tip-in issue/stumble (3.0 5-speed)
 

I have a throttle tip-in stumble that seems fairly common for the M54 engine but in doing research haven't found any smoking guns. Before I open up the parts cannon I wanted a bit of help troubleshooting. Just over 160k miles on the vehicle and pretty much all original except for the stuff I've done.


Just off idle, when trying to accelerate, the engine feels like it bogs down for a split second before it catches. Once it catches, the engine feels healthy.


I've been poking around OBDFusion and INPA for anything obvious. The sample rate is slow for either so its hard to see transients like this, but nothing obviously off with the mass air flow, air intake temp. I also did a smoke check on the intake to check for vacuum leaks and did not find any. Long term fuel trims on both banks is +1.6%. No stored codes.


I've already replaced the plugs and the VANOS seals as I read these can cause similar symptoms, no obvious difference from either. I have not yet replaced the coils, MAF, or O2 sensors.

One thing that seems odd in INPA - checking the PWG/MDK values (the pedal position sensor vs throttle position sensor), intuitively these should roughly be in sync with each other unless I am understanding this system incorrectly. I assume there are redundant sensors for both to measure the driver's desired throttle input and and actual throttle position. the PWG sensors react immediately but the MDK ones barely change. Also, the sensors for each set aren't in sync with each other (i.e the two PWG sensors have an offset, and the MDK sensors appear to be inverted, one reads 0.5 volt and the other reads 4.5 volt). I posted two images, one at no pedal input and the other with some nominal level of throttle input. Does this mean there's something up with my throttle body?


Any help here is appreciated. Oh, also this is one of those rare 5-speeds. Other than the tip in issue it's great fun to drive!

I thought both the pedal position and the throttle position used inverted secondary pots. I haven't polled mine in a while and can't remember for sure.

If i get a chance i can look but newer chassis so there is a chance they changed since then.

Have a search among the E46 crowd…If anybody has figured it out, it’s the e46 crowd…


No disrespect to this forum…

https://www.e46fanatics.com/threads/...ix-mod.946536/

From trolling the E46 forum, that's what I thought too. What I'm seeing doesn't make a lot of sense.

Yeah I've been reading on the E46 forum and bimmerforums. So far I saw one guy who said a new MAF fixed it, and another who said he had excess carbon buildup from running hot.

MAF is a good guess but you won't know until you replace it. Carbon could be a problem especially if you aren't using premium fuel.

I haven't used either, but what about Sprint Booster OR mapping the throttle yourself with MS4x.net ?

They look more promising than the MAF or carbon buildup.

https://www.e46fanatics.com/threads/...oster.1315523/

I've only had the car for about six months so not sure what fuel the previous owner used. I have Bg44K in the tank just in case.

My E36 had the carbon build up problem, about as bad as you could imagine. 25 years of New Jersey 87.

It was consistently the same throughout the entire rev range, nothing unusual off the line. It was just bogged down and tired through the entire rev range. You give it full throttle and it didn't want to do it.

I ran a few cans of berryman b12 through the fuel and the crankcase, that helped a little bit. I used the liqui Moly engine flush twice, that helped a little more. A lot of people say not to use that as it can dislodge something etc but I've used it a bunch in all my cars and been lucky. It does help. But I still had to take the head off and clean it by hand. It's normally responsive now, but I did about 60 other things in addition to the carbon cleaning.

I don't think carbon is your problem.

My f30 does all this kind of crap, it's the computer. The dsc, and the e differential, torque , limiter, dual mass flywheel protection nonsense. Some of this can be coded out but it's an uphill battle on that car. Sometimes off the line I'll get exactly what you describe, and then into second it cuts out. Then there's shadow codes for flywheel protection.

I am thinking about this. It does feel like it could be software or a protection thing like you describe. Maybe there's a software limited throttle or power application depending on clutch position? I did notice the clutch switch shows "disengaged" in INPA until the very top of travel. One of the things on my list is to check that switch wherever it lives. I know on the old Hondas I used to have that switch was adjustable.


Edit: Looking at the replacement clutch switch it doesn't look adjustable. Darn.


To clarify though - your E53 does not have the same problem as I describe, correct? i.e it's not an intended effect of the programming that would have been present in the car when new?