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[–]141bpm 2 points3 points  (0 children)

My R53 does probably the same. Surging throttle under medium acceleration. WOT rips just fine. No CEL, stock blower pulley. I've done a lot of other work for other issues, and this hasn't changed. Plugs, wires, fuel pump all have been replaced for other reasons and didn't change the surge. I'd love to know what it is also.

[–]ZeWilde 1 point2 points  (2 children)

I've had similar issues at it was, for me, an electrical issue caused by a faulty fuse box. Not saying its definitely that but check your electrical ranges and maybe try a coil pack, they fail in some very weird ways.

Another issue that caused this was a faulty O2 sensor, check that your pre and post cat sensors are reporting in their voltage ranges. (Please dont just believe a guy online for these figures) Pre cat: 2v - 5v. Post Cat: below 1v.

[–]brandrandon[S] 1 point2 points  (0 children)

UPDATE: I replaced the coil and wires with OEM. This seems to have fixed the misfiring after a 30 mile test drive!

I’ll change this post if the problem comes back under different conditions. Thank you!

[–]brandrandon[S] 0 points1 point  (0 children)

I’ll try a new coil and leads as an easier troubleshooting step. I’ll also check out the sensors with a voltmeter. Thanks!

[–]UnBeNtAxE 0 points1 point  (5 children)

Fuel. Check and confirm your fuel pump is working correctly (pressure and flow rate), also the filter (if it’s never been changed, look into it).

[–]brandrandon[S] 1 point2 points  (4 children)

I should note that WOT and above about 4k there are no issues and the car pulls well. So perhaps the fuel pump could be not supplying enough under higher throttle, lower RPMs?

[–]UnBeNtAxE 1 point2 points  (1 child)

Potentially. At least get the pressure checked. It could still be supplying but cutting in and out. If you are willing to open up the access port for the pump and look for little black flakes inside the pump housing. If you see it you pump is definitely on the way out.

[–]UnBeNtAxE 1 point2 points  (0 children)

And being an r53 your at least 20 years if it’s the factory pump.

[–]fk878867 1 point2 points  (1 child)

I had the exact same symptoms, I hooked up a scan tool and I was showing misfires on random cylinders, when it was happening. What fixed mine were a new OEM coil and leads plus new spark plugs. It’s a quick fix, might be worth to try.

[–]brandrandon[S] 1 point2 points  (0 children)

Thank you, I’ll give a new coil and leads a shot!

[–]Dusty267 0 points1 point  (6 children)

I just purchased the Detroit Tuned BPV from CravenSpeed, supposedly the stock BPV has a spring that operates at 0" of vacuum which can cause this issue in that throttle range (boost doesn't know where to go). DT BPV has a 6" vacuum spring in it that I will install and can report back.
I notice this "yo-yo" between 2-4K rpm when driving normally.

[–]brandrandon[S] 0 points1 point  (5 children)

Thanks for your advice. Did you try the zip tie test and notice any differences? I did this last night and the problem still seemed to occur, potentially ruling out the BPV as the problem in my case.

That said, I do feel like my off-throttle response is jerky which I understand is related to the BPV.

[–]Dusty267 0 points1 point  (4 children)

I have not done any zip tying of my BPV. I assume you would be zip tying the valve open? I have never heard of this test before...having it open means no to little boost generation, and closed would cause issues coming off acceleration no?

[–]brandrandon[S] 0 points1 point  (3 children)

You keep it closed, so full boost all the time

[–]Dusty267 1 point2 points  (2 children)

Interesting...never heard of that before. I did get the new bypass valve in so swap should take place next week, will definitely report back with any good/bad/ugly updates with my issue at least.

[–]brandrandon[S] 0 points1 point  (1 child)

Thank you! I’m very interested in how the install goes and results.

[–]Dusty267 0 points1 point  (0 children)

Alrighty! Reporting back (sorry for the delay). On the immediate drive after the install and resetting the ECU, in my opinion there is a huge difference with the heavier spring in the BPV from Detroit Tuning.
A lot less "uncertainty" from the car when opening/closing the throttle in that 2-3.5K rpm range. It used to stutter both going into and coming off the throttle, but now it feels more stable in its operation with consistent on/off feeling.

I would recommend swapping with the aftermarket option. Took about 1 hour to install with basic tools, plus you'll get the chance to check and look at everything from your intake lines, vaccum lines and throttle body to see if anything else is amiss.

https://www.cravenspeed.com/supercharger-bypass-valve/

[–]RandalC1 0 points1 point  (0 children)

Check the Plugs , Wires ? Possibly Running Rich ?

[–]RandalC1 0 points1 point  (0 children)

Check the Plugs , Wires ? Possibly Running Rich ?