Jerky acceleration during light throttle, low RPM

[az3579]

I've been chasing this problem for a long time now.
When I start from a stop, I accelerate very lightly and shift at around 2k because I like nice smooth starts. The problem is that for a while now, my car has had very jerky acceleration in this rev range when I apply light throttle. This is very hard to describe in text, so I took a video to show this.

Note when you watch the video that all the camera shaking while in first gear is caused by the jerky acceleration, not by bumps in the road.

https://vimeo.com/129172134

Also note that there is no loss of power anywhere in the rev range. The car does not idle erratically and it pulls cleanly throughout the rev range.


Any ideas?

Things I've replaced that should be relevant:
O2 sensors
Spark plugs
Ignition coils
MAF
Intake boots
Throttle body
Perhaps some other things I'm forgetting about...

[danewilson77]

I thought the coils fixed this?

[az3579]

I thought the coils fixed this?
That's what I thought. Apparently it was just wishful thinking because I ended up noticing it again.

[derbo]

Fuel system seems to be the next thing to verify its good. Outside that, maybe vanos or camshaft sensor...


Sent from Mobile

[BMWCurves]

Fuel system seems to be the next thing to verify its good. Outside that, maybe vanos or camshaft sensor...

My sister's 2000 Jetta had a faulty camshaft position sensor and it would have really uneven acceleration to the extent that sometimes you would accelerate and it would sputter and then flop back down to idle even with the accelerator to the floor. Not sure if this is the same thing, but definitely a good suggestion.

[slater]

My sister's 2000 Jetta had a faulty camshaft position sensor and it would have really uneven acceleration to the extent that sometimes you would accelerate and it would sputter and then flop back down to idle even with the accelerator to the floor. Not sure if this is the same thing, but definitely a good suggestion.

what would be awesome is if we could datalog those sensors' output and compare it against a non-sputtering car.

peter

[az3579]

what would be awesome is if we could datalog those sensors' output and compare it against a non-sputtering car.

peter
I've thought about doing this once I found out what to look into. I'll have to see if I could find a function in INPA for this.

[danewilson77]

My sister's 2000 Jetta had a faulty camshaft position sensor and it would have really uneven acceleration to the extent that sometimes you would accelerate and it would sputter and then flop back down to idle even with the accelerator to the floor. Not sure if this is the same thing, but definitely a good suggestion.
I bet she had an SES light though. I don't think BP does.

[az3579]

No SES light. But, then again, I've had stuff go bad before without an SES light, so who knows. I'm gonna see how much these sensors cost and how labor intensive it is to do throttle position sensors and camshaft sensors. I might as well do them anyway considering the mileage, even if they don't resolve the problem, because those things can leave me stranded.

[BMWCurves]

I bet she had an SES light though. I don't think BP does.

Nope, no CEL or SES lights. It took forever to diagnose because the codes being thrown were misfires and MAF sensor but nothing about the cam position sensor.

[ryankokesh]

Have you tried adding washer fluid? :dunno









.... sorry.

[ryankokesh]

Is the fuel filter due to be replaced?

Does the car being warm/cold change anything?

Is there any chance it could be anything involved with the clutch?

How about the pedal module thing? Is that something you can clean with electrical contact cleaner stuff?

You've done Vanos, right?

[Vas]

Have you tried adding washer fluid? :dunno









.... sorry.

This lol. Good one

[wiggle_puppy]

This is interesting. I have a similar issue, except mine occurs around 3,000 RPMs and is typically more noticeable in 3-6 gears. It's a "surging" feeling on light throttle.

New intake boots, primary O2 sensors, DISA okay, Besian VANOS, updated DME...still have the issue.

Have you updated your DME?

[az3579]

What's really weird is that today it felt closer to "fine" than most days. It's been crappy for a long time now but today it felt better for a while. It's back to crap again though...


Is the fuel filter due to be replaced?

Nope, already replaced.



Does the car being warm/cold change anything?

No different.



Is there any chance it could be anything involved with the clutch?

Definitely not clutch related.



How about the pedal module thing? Is that something you can clean with electrical contact cleaner stuff?

Not sure what you're referring to. What module do you mean?



You've done Vanos, right?

I did seals a few years ago (Beisan), the first time I met Dane... That was before 100k miles though. I have almost 223k now...
Torque feels fine. Do you think this really could be it?

This is interesting. I have a similar issue, except mine occurs around 3,000 RPMs and is typically more noticeable in 3-6 gears. It's a "surging" feeling on light throttle.

New intake boots, primary O2 sensors, DISA okay, Besian VANOS, updated DME...still have the issue.

Have you updated your DME?

[Dave1027]

Have you tried cleaning the ICV?

[ryankokesh]

Dunno about the VANOS...just a wild guess. The pedal module I meant is just whatever the electronic piece is that tells the car how far down you're pushing the pedal. Another pretty wild guess.


Sent from my iPhone

[az3579]

Dunno about the VANOS...just a wild guess. The pedal module I meant is just whatever the electronic piece is that tells the car how far down you're pushing the pedal. Another pretty wild guess.


Sent from my iPhone
I figured if the throttle pedal potentiometer was bad then I'd have an issue with it at other RPM's too if I hit the troublesome part of the potentiometer... I have no problems with the throttle above 2k and it responds to all inputs regardless of how lightly or heavily I'm pushing the pedal.

To respond to the question if whether I've updated my software, no I haven't. I haven't yet figured out how to update my DME with WinKFP. I wanted to do this anyway at some point when I'm ready to buy new software to take my mods into account.

[txImolafan]

I was having a problem similar to this, I updated it and it solved the problem.

[az3579]

I was having a problem similar to this, I updated it and it solved the problem.
Thanks for the info. I'll make updating the software one of my priorities.

[derbo]

one step closer to resolving this. :crosses fingers:

[az3579]

one step closer to resolving this. :crosses fingers:
Hopefully...

[ryankokesh]

Well, if nothing else you know a lot of things it's not!


Sent from my iPhone

[ELCID86]

I was wondering if it was cam position sensor in my car and bought one just in case ( not sure if I had the same issue as you). The new coils helped but I still have some hesitation in the 25-3500 range. I plan to do the VANOS and cam sensor soon.

I'd like to get my dme updated in case that's part of.y problem too.

Can someone at the meet update dme? (I'm not driving, asking for BP).

Thumbs, iPhone, Tapatalk.

[az3579]

I was wondering if it was cam position sensor in my car and bought one just in case ( not sure if I had the same issue as you). The new coils helped but I still have some hesitation in the 25-3500 range. I plan to do the VANOS and cam sensor soon.

I'd like to get my dme updated in case that's part of.y problem too.

Can someone at the meet update dme? (I'm not driving, asking for BP).

Thumbs, iPhone, Tapatalk.
Not sure I'd feel comfortable flashing my DME over 700 miles from home... Doubt anyone has anything other than a trickle charger as well. I believe I need something that can sustain constant voltage. Anyone who has used WinKFP care to chime in?

[derbo]

Not sure I'd feel comfortable flashing my DME over 700 miles from home... Doubt anyone has anything other than a trickle charger as well. I believe I need something that can sustain constant voltage. Anyone who has used WinKFP care to chime in?

You will need a charger that can sustain 12V (most likely 14~V)

[ELCID86]

Good point BP on the repairs on a road trip.


Thumbs, iPhone, Tapatalk.