VStar650CL wrote: ↑

Thu Sep 09, 2021 4:08 pm

The brake switch adjustment procedure in the ESM may not help, N/I brake switches are notorious for sticky contacts and for the two throws in the lamp switch getting "out of sync" with one another from contact abrasion. When that happens you need a new switch and not an adjustment. However, I really doubt that's the problem. N/I vehicles are very good about throwing DTC's if there's a brake switch conflict, although they often blame the pressure sensor for what's actually a bum switch. Since you don't have DTC's at all, that's probably the wrong tree to bark up. The only thing that might be happening is the switch "falsing" and turning on the lamps when they shouldn't be on, causing the tranny to refuse to accelerate. That's easy to diagnose if you can see the reflection from your third brake, just look in the rearview next time it acts up and see if the lamp is on. If so, replace the switch.

I also doubt it's the ABS, unless you're hearing actuator noises from one or both rear wheels when the surging happens. When there are no codes it's generally the steering angle sensor acting up more often than wheel sensors, because N/I ABS's throw wheel sensor codes at the first missed tooth, they don't wait for a repeat. So same deal, without DTC's the ABS isn't the most likely suspect.

Most scanners read short and long term fuel trim (STFT/LTFT) and not A/F-alpha, which is peculiarly Nissan. So I'll stick with STFT/LTFT. Generally STFT will sit slightly rich (typically 1~3%) at warm idle and go slightly lean when you raise and steady at a higher RPM. What you really need to check first is LTFT. If it's more than a few percent rich or lean on either bank then there's an underlying issue of some sort, possibly fuel quality, vacuum leaks, PCV valves, etc. If the LTFT's are normal then it means your surging is an intermittent problem that the ECM doesn't recognize and isn't attempting to compensate. If one or both LTFT's are very rich and you don't find a vacuum leak on that bank, there's a good chance the A/F sensor is the culprit (dying A/F's almost always cause rich compensation). A/F's are what used to be front O2's, by the way. They work differently, directly metering rich/lean above and below a set voltage threshold (usually 1.5V or 2V). They respond much quicker than HO2S's, so they're much better for direct mixture control. Nowadays HO2S's are pretty much relegated to working for the government, monitoring the cats. A/F's are used in front, where it matters to the engine.

This smells pretty much like a MAF issue, so if you find short or long term alphas out of kilter on one bank, try swapping the MAF's and doing an IAVL. Then drive for awhile to see if the problem changes banks. If it does, then that MAF is lying to the ECM and causing your problem.