[alexwhittemore]

I had coil go on me a few weeks ago, which of course caused huge hesitation under any load and seriously reduced total power. Brought it in to the local dealer and they covered replacing all 6 under the SULEV warranty.

A day or two ago, and I’m not sure if this has been true since getting the coils replaced, I noticed a weird little hesitation between 1500 and 2000 RPM, especially right on 1700. Also, it seems to only happen in 3rd and 4th gear (that I can tell easily). It’s pretty slight - maybe 5% as noticeable as with a dead coil. But it’s just enough that, if I need to scoot on the highway and happen to be right around the problem RPM band, the car just won’t change speed like I expect, or else if I’m really accelerating, I have to wait the extra quarter or half second before it down-shifts out of the problem zone (auto trans).

What’s particularly weird, if I try to reproduce the problem on an open stretch of slow road and I feather the throttle just enough to notice the hesitation but to not cause a shift, I actually see an RPM decrease with increasing throttle. Like, start pushing the gas around 1650, RPMs will inch up to 1700, then dip back down to 1600 without ever pulling off the gas.

I tried resetting the throttle adaptation, which seems to have covered up the issue a bit. But I’m not convinced it’s gone, and I think the adaptation reset is probably just covering up the real root cause.

There aren’t any engine specific codes like intermittent misfire or anything, even if I try hard to reproduce the issue for as long as I can. The only codes I’ve got right now are electrical power related, 2DEB and 2DED. 2DED is “standby current control” - that one’s almost certainly popping up because sometimes I plug a phone in in my trunk, to a direct-wire socket I added that never turns off (so, the phone will continue pulling power long after the car enters low-power mode). 2DEB is “power management network failure” - that one I’m a little more worried about, since I’m not certain it’s a direct result of my phone charging. I do think my battery is probably a little weak (never been replaced, that I’m aware of, at 120k miles, and definitely not for the 80k I’ve owned it), but I don’t know what that’d have to do with a hesitation in one particular spot.

[stevesingo]

I had exactly the same on my MT car. An application of throttle, going from 30% to 70%, between 1500-1700rpm led to a hesitation where the revs dropped for 0.5sec before it picked up as normal.

I connected the car to inpa and ran the VANOS test where you specify a target cam angle and the DME tries to hit that by varying the VANOS valve duty. Mine looked reall sluggish on the exhaust side, and this was backed up when monitoring the cam angles when driving.

I removed and cleaned the solenoids and oils supply check valves, but this made no difference.

I replaced the VANOS solenoids with new genuine and it cured the problem.

[alexwhittemore]

Damn, I was hoping you wouldn't say that

[alexwhittemore]

Originally Posted by stevesingo

I connected the car to inpa and ran the VANOS test where you specify a target cam angle and the DME tries to hit that by varying the VANOS valve duty. Mine looked reall sluggish on the exhaust side, and this was backed up when monitoring the cam angles when driving.

So I'm sure I can probably find the VANOS test you're talking about in INPA, but assuming I do run it, what's the definition of "sluggish" per your experience? Did the exhaust side seem off because the intake side was much faster to hit the setpoint, or what? And I assume this is with the engine running?

I just set up a service appointment for Tuesday - if VANOS solenoids are bad, that should be covered by the SULEV warranty on my N51, and this dealer is great in my experience with emissions warranty coverage. But especially since I'm not getting any codes yet, I feel like there's a wide margin for error on the diagnosis that could bite me.

[stevesingo]

Originally Posted by alexwhittemore

So I'm sure I can probably find the VANOS test you're talking about in INPA, but assuming I do run it, what's the definition of "sluggish" per your experience? Did the exhaust side seem off because the intake side was much faster to hit the setpoint, or what? And I assume this is with the engine running?

I just set up a service appointment for Tuesday - if VANOS solenoids are bad, that should be covered by the SULEV warranty on my N51, and this dealer is great in my experience with emissions warranty coverage. But especially since I'm not getting any codes yet, I feel like there's a wide margin for error on the diagnosis that could bite me.

The sluggishness is pretty clear to see. when hitting the cam angle set point button, you should expect the cam to almost immediately swing on to target. Mine didn't, it took maybe 0.5sec despite the engine idling at 1500rpm where there should be sufficient oil pressure.

Mine never showed a CEL, but it did record a cam sensor code, presumably due to the cam sensor not seeing a value which is consistent with the duty cycle on the VANOS solenoid.

I don't know what the criteria is for SULEV warranty. I would guess, as the CEL is primarily there to alert the driver of a fault which effects the emissions, the SULEV warranty will depend on a CEL. Hopefully the stored code is enough to trigger a claim.

[alexwhittemore]

SA unfortunately said "no light, no coverage," which also means my fuel filler neck issue won't ever get covered.

I don't have a CEL, but I also don't have any related codes. I noticed on the way home in "M" trying to aggravate the issue that I couldn't - it seems, if not completely gone, at least not noticeable unless the transmission is in D.

Is it possible either A) that it's not VANOS at all, but transmission related, or B) that when the transmission is in M, cam angles get set earlier, so a lag is less noticeable? Like maybe they're set for optimum power at current RPM, rather than being set for optimum efficiency then slewing to power when you hit the gas?

[alexwhittemore]

Situation update: Let it slide for a month, having no time to diagnose. Out of curiosity I ran Carly again last night and there was a new code! 2AAB, vairable intake (self diagnosis). According to the bentley manual, that actually means variable intake actuator 1 fault.

Made some time this morning to rip everything apart and have a look.

FYI, it's relatively easy to get at the DISA valve, but the easy route in is to remove the cabin air filter shelf above the engine, pull the intake air filter box, and pull off the intake hose from the throttle body. I also moved the brake fluid reservoir too, but you might not have to. With the air parts out of the way, DISA 1 pulls right out.

Anyway, sure enough, I pulled the (large, left, first) DISA valve and it's just flapping around. The vane is driven by a worm gear, so it should not be free to move by external force, in any position.

Bought a replacement, PN 11617579114, on eBay. Will advise if it looks of much worse quality than the OEM part, but I think it's hard to get cheaper or crappier than the genuine BMW so I'm not too worried. $171 vs $270 OEM or $220 aftermarket from ECS/BavAuto - I'll take the gamble. https://www.ebay.com/i/222869401427?chn=ps

[alexwhittemore]

Update again: Installed the new DISA valve. Situation has improved, but the original issue is still present. Following in https://www.e90post.com/forums/showt...=916892&page=7