Hey guys, I've searched and searched and found no answers, so here I am with a question for the forum...would be grateful if someone can help me out or point me in the right direction. I've got an issue with surging under relatively heavy acceleration. It's like someone's flipping an on/off switch on the throttle every half second when I'm above 4000rpm.

It's a hot chocolate brown 2011 MCS, manual, N18, 122k KMs, entirely stock, except for a JB4 I plugged in about 18 months ago. Last summer I started experiencing a yoyo like effect on moderate to hard acceleration, much more pronounced when the car is cold. I had some CEL codes for the VANOS solenoids, so I replaced both. The problem was still there. I then decided to go ahead with carbon cleaning. Again problem still there.

Last week I decided to take it to BMW/Mini. The replaced my high pressure fuel pump under the extended warranty. They said the found fault codes in the system for the HPFP. They also replaced the footwell module and an auxiliary water pump, all at no charge to me (awesome for an almost 10 year old car). I had removed the jb4 several days before bringing it in.

I'm still experiencing the surging over 3500-4000 RPM though. I haven't put the JB4 back on. The BMW service tech tells me next steps are to make sure the valve cleaning was actually done by my other mechanic (no reason not to trust it was done) and then consider changing the hot film air mass meter. Then it would be on to investigating the injectors. He told me these would all just be guesses at best at possible culprits. He said they had their BMW techs look at my car's data and they've only seen this issue once before (for all of Canada) and they weren't able to fix it.

I've read up on the issues the R53 Minis had with yoyo acceleration (yo-yo Chronicles thread), and that seems to be exactly what I'm experiencing. On those R53s, it seems the issue is fixed by replacing/fixing the supercharger bypass valve. Wondering if anyone knows if the bypass valve on the r53 is synonymous to the function of the air diverter bipass valve on our turbocharged N18s?

If anyone has any insight into the problem, i would appreciate it!! I'm so frustrated trying to figure this out. Just want my fun trouble-free car back

 

Curious....with regards to the MAF sensor possibiltiy, are you using stock airbox and paper filter or aftermarket foam filter ?

Did he check the Turbo's impeller bearing ?

 

I’m using the stock air box and paper filter. And no I don’t believe they looked specifically at the turbo bearing though I was told they looked at all the likely culprits. Even asked me what octane fuel I use. I’m somewhat mechanically inclined. Is that something I can check myself?

 

This is a totally different direction. I had an issue that sounds similar though. A lurching back and forth at speed. It was sporadic. Usually in the 3000-4000 range in 3rd and 4th gear. But it happened in 5th and 6th too. I could actually see the tachometer fluttering up and down when it was happening. It wasn't swinging up and down wildly or anything. Just a wobble in the needle and a definite chugging sensation from the car. If I let off the accelerator and got back on it, it usually went away. Passengers felt it too.

Anyway, replacing the accelerator pedal solved the issue. The throttle position sensor on there can go bad. It was super easy to replace too. One bolt and one plug. Pelican has a decent guide at: https://www.pelicanparts.com/techart...eplacement.htm

My car is a manual, this is the part I used: https://www.ecstuning.com/b-hella-pa...426853177~hla/

(edited for typos)

 

interesting. Thanks for sharing your experience. I will look into that. Curious, how did you diagnose the situation with your car? Was it throwing a code?

 

It was not throwing a code or error on the dash and I did not hook anything up to look further. Since it went away when I let off the accelerator and seemed to stay away when I pressed the accelerator again, i was thinking something in the throttle body. I found an article about how to check the voltages involved to properly diagnose the accelerator's throttle position sensor and adjust it. I am not 100% but I think it was this one: https://www.carboncleaningusa.com/th...oper-1-6-l-115 . The pedal was not an overly expensive part and easy to replace.

I have two minis (wife and daughter) and my first thought was to just swap pedals. But it is a different pedal between manual and automatic. If you know someone with a compatible model, maybe you could arrange a test swap and see if the problem follows the pedal or stays with the car.

After I replaced the pedal and let it idle a while (per Pelican's write-up) it ran a lot better but not perfect (at first). I still noticed the problem on my first test drive. But much less drastic and probably improved by 75% or so. Have not noticed again since that first drive. That was about 2 months and 500 miles ago. It's running great now and everyone in the family that drives it has commented on that fact.

 

You’ve renewed my optimism in figuring this problem out. Our problems sound very similar so I’m going to go ahead and swap the pedal. Unfortunately a friend of mine has an R56 but it’s an automatic. Thanks again. I’ll post back my results in a few weeks.

 

Any resolution yet mike88? Really curious how this ended up for you.

 

I’ve been meaning to log in and post on here for about a week now. Thank you so much man. I ordered the pedal and installed it about 2 weeks ago now. The first drive the problem was still there, maybe 25% less pronounced. The second drive the issue was 50% better. 3rd and 4rth drives there was just a hint. And I’d say since then it’s all but gone. I do feel a bit of something still, but I wonder if I do need maybe a fuel line cleaner treatment or something like that.

I can’t thank you enough. I probably never would have found the issue. I had BMW technicians telling me it was probably characteristic of the car. I’ve been meaning to get in touch with that tech person to let him know as well. Honestly I really appreciate you taking the time to post the suggestion. Life saver to me. I might have sold the car as it was borderline unbearable to live with if it weren’t for your post. Thanks thanks thanks!!

 

Awesome! That's good to hear. Glad it has worked out. The computer is supposed to learn and adapt over time so maybe it will continue to get better.

 

I hope so. Just glad to have my fun to drive car back. I still haven’t plugged the jb4 back in. I might leave it off.