After attempting to pass some tasteless rube in a blacked-out '01 Audi A6 (with the n/a 2.7 V6 ... for shame ), who was driving like a donkey's anus, I cut into limp mode.

I downshifted to fifth, buried the throttle, but found that my boost gauge was only registering .02 BAR at 3,750 RPM at WOT. Something was clearly amiss. The car simply did not accelerate, and *BOOM*, limp mode.

Tending to my bruised ego on the shoulder of I-55 with my hazard blinkers on, I fired up my OBD scanner and found I had P0107, P0500 (I had just replaced a wheel speed sensor reluctor ring [wheel bearing assembly] on the pass. side and forgot to clear the code), and the dreaded P1688 - "Electronic Throttle Control Monitor Level 2/3 Mass Airflow Calculation."

Having been through the same drama when both my MAP/TMAP sensors were on the fritz, I shut the car off, started it again, and the limp mode disappeared, as to be expected.

Here are the symptoms while driving:

- Car will idle roughly for 1-2 seconds, randomly, at startup/idle
- "Yo-yo" effect at approx. 24-25% throttle during tip-in at cruise, or while climbing up a hill
- Lowered maximum boost level (.7 BAR, now that it's cold, vs. 1.15 BAR when it was warmer)
- Sluggish throttle response (difficult to heel-toe/rev-match on downshifts)
- Accessory Drive Belt squeal in the damp/rain

Here's what I have found during a cursory, parking lot investigation:

- Belt tensioner showing upper 2/3s of the first hole (belt was replaced last April with a NAPA/Gates 60532)
- Bypass/Shut-off Valve seems to have adequate spring pressure, holds all the way open at idle
- Alta V.1 17% underdrive S/C pulley is not wobbling or loose
- PRW FluidGel Damper not wobbling or loose (I ditched the OE pulley/damper last year)
- Throttle body harness seems okay (checked it this past April while doing clutch - no frayed wires or loose connections)
- Throttle body appears to have been opened at some point by the previous owner: there's a spot that appears to have been drilled through and sealed up with epoxy.

I am at my wit's end with this car. It's just one problem after another during my last two years of ownership.

So, the question: based on these symptoms, what could the problem be? I understand I may also have a blend of all of these problems, knowing my luck.

 

Did batt light turn on w/ the SES? Check your belt size, might be some belt slippage issue. Just 2/3 of 1st hole? Also, check if your PRW didn't loosen. How's your BPV spring? That's a known culprit for yoyo. When was your last fill up? Bad gas can cause a lotta problems.

I doubt you'd have the same issue as mine a coupla months back. Some common symptoms, no limp mode though, no codes. Ran so lean, very difficult to start & had bad yoyo, practically undrivable. My harmonic damper even died in between all these issues. Investigated plugs, wires, coil pack, BPV, Vac lines, Pressure regulator, filter, pump....only to find a torn fuel hose from pump to filter. Replaced that & got awesome back! This case was buried under the X-Files over @ the 'alliance', & had a lot of help there.
Best to go thru by elimination. Hope you'd sort it out.

 

Battery Light

No battery/voltage light. I'm running a shorter belt than a 60535, which is the recommended belt while running a 17% pulley. This leads me to discount the slipping belt theory, as below.

Belt

When the belt was new, the top of the 2nd hole on the tensioner strap was just barely visible. This indicates the belt has stretched, but even with 2/3rds of the first hole visible, it *should* still be good. The 60535 I ran before didn't even show the first hole on the tensioner strap.

The reason why I am discounting the belt as a possible source is I don't get the "burning rubber" smell associated with a slipping belt. A visual inspection seems to confirm this.

Then again, that would not explain why the belt squeals in the rain or an otherwise damp condition (drive-thru car wash).

Crank Pulley

The PRW crank pulley does not *appear* to be loose, however, I am limited in my ability to diagnose these faults while the car (and I) is at my apartment in the city. I will have to travel to my father's garage, put it up on the lift, and check the pulley for play. If it was loose enough to confirm by putting my hand around the pulley and pushing/pulling on the pulley, it would wobble visibly with the engine running.

Bypass Valve Spring

The tension *appears* to be good. While the car is off, the spring pushes the butterfly shut, but (and this may be psychosomatic) the actuator arm doesn't seem to be "snapping" shut like it used to. It almost feels ... Viscous, if I were to describe it. Like the spring housing was filled with molasses. The spring seems to stiffen up toward the end of it's travel when actuating the arm by hand as well.

I've read up on a few threads about BPVs sticking in the "open" position causing a P1688. I've done the VGS mod, so theoretically, positive pressure should be helping the spring push the diaphragm shut. I've also noticed a loss of boost pressure on throttle tip-in. I'm beginning to suspect I have a leaking diaphragm and a weak BPV spring.

She's got about 87k on her as well, and at this mileage, BPV failures are common. I'm going to put money on my suspicions that the BPV is to blame.

Throttle Body

I suppose my next question should be, how do I confirm that my throttle body is working correctly? Is there a diagnostic process involved?

 

Thanks. A torn fuel line from the pump to the filter? Doesn't that line run on top of the gas tank, between the rear seat pan and the gas tank? How in the hell did that get torn up, and how was it not leaking? Rodents, I suspect?

 

Try to reproduce the problem. If it happens again, get another used TB for cheap, and try to reproduce again (or borrow one?) Who knows wtf the other guy did to the one one the car.

 

The only thing stopping me from buying a new throttle body is the fact that on '05-'06 cars, the harness is usually suspect.

Then again, I checked the throttle body harness up to the junction to the main harness and none of the wires' sheathing were torn or damaged in any way ... This is why I'd like to know if there is some way to test the operation of the throttle body.

If it were a simple cable-actuated throttle body, this wouldn't be a problem. I hate technology sometimes ...

 

That's why this was buried in the X-Files. The torn fuel hose is submerged in fuel, inside tank. Fuel pump has never been serviced, 1st time to have changed filter too. After a decade, it probably just hardened, turned brittle & tore. The boards have never seen nor heard anything like this, mine was a 1st, I guess. My tank is definitely rodent-free.

TB is something you might have to look into. Aside from a bad harness, a dirty 1 definitely would cause terrible idling & drivability.

 

Well, it's official. The car is not building boost at all, at any RPM. Attempting to give it the beans will result in limp mode. It's probably the bypass valve, which seems stuck open.

I have a rattling timing chain as well. Fantastic ... Just what I need before the bar exam ...

Good thing I ordered the chain tensioner awhile back, but this is still pretty annoying. Guess I'll order the Detroit Tuned bypass valve.

 

Well, the car's been trailered back to my parents' garage. It'll have to sit for the next month or so. I will report my findings as I troubleshoot. I've ordered the Detroit Tuned BPV and a brand new OEM throttle body, so I'll start with those.

 

Hope it'll get sorted.

 

Throttle body will not cause a lack of boost. I very much doubt this is the problem. This code comes when the engine demands/expects a certain measured by the intake MAP at a given RPM but does not have meet the requirement, thus setting the check engine lamp on and putting the car in limp mode. Most 1688s I've encountered are either: A damaged harmonic balancer, slipping belt and/or supercharger pulley, failing BPV, or in a few other circumstances- a crankshaft pulley "walking" on the crankshaft due it not being torqued down enough. I have not encountered any small intake manifold leaks yet (cracked hoses/boost tubes, etc), but I would imagine this code to be present if that were the car had any leaks. These can be found with a smoke machine, using a hose and some propane, or a tuned ear.

Furthermore, MINI updated the weak spring encountered in the R53 BPV: A stock unit will suffice for any application. I would first check to see if your crank pulley is fully torqued and belt is not slipping, then make sure the BPV is working properly. Good luck and keep us posted.

 

Thanks for the input!

While belt slippage seems a bit unlikely to me, I will admit that I re-used the TTY crank pulley bolt after putting some red loctite threadlocker on it. I did double-check my torque-specs when I replaced the OE pulley with a PRW crank pulley, and checked it again when I replaced my belt last spring. It checked out.

This may or may not be a foolish question, but can re-using the TTY crank pulley bolt cause the pulley to walk on the crank snout? I did a visual inspection of the crank pulley and had someone rev the motor, and did not see any wobbling.

 

Not that I've seen. The only way to confirm the pulley walking is to remove the bolt, scribe both crank and pulley and reinstall the bolt, recreate the problem, then remove the bolt and look to see if the pulley has walked. re-reading your symptoms, I'm putting my eggs in the BPV basket.

 

Sitrep: I replaced both the throttle body and the bypass valve with a brand new OEM throttle body (production date 2011) and DT BPV this past weekend. I also did the timing chain tensioner while I was at it.

It appears I was wrong about the problem. After removal and inspection, my OE bypass valve wasn't sticking open, nor was the diaphragm torn. The car still wouldn't build boost, and the knocking, rattling sound was still present when idling and revving the motor.

After using a very long flathead screwdriver as a stethoscope (which I should have done from the get-go), I pinpointed the problem to the belt tensioner. A friend and I initially suspected the supercharger pulley, since the sound appeared to have originated from the snout/gearbox, but putting the screwdriver on the tensioner strap (which was quite wobbly) produced the noise I was hearing, which is similar to loose gravel put in a cement mixer.

I will try and post a video of the tensioner before and after I swap it out for the new one ($97 shipped from RockAuto's warehouse in Ohio) and get my hands on a NAPA 60532 belt, but for now, this looks like a closed case.

 

Well, the plot thickens.

I removed the tensioner assembly today and found that it wasn't the culprit. While the damper was shot (oil leaking from the tensioner damper, caking the tensioner with oil and dirt), the more pressing issue was the supercharger pulley, which basically fell to the floor while removing the belt.

I was running an Alta V.1 17% underdrive pulley, which mounted to the supercharger shaft via an interference-fit tapered shaft coupling.









The pulley basically came loose and scoured the hell out of the supercharger snout shaft drive. I measured the snout and came up with the following measurements: outside of snout shaft (away from supercharger): 19.74mm, middle of snout shaft: 19.78mm, bottom of snout shaft (right up against the supercharger): 19.94mm.

I don't know what the stock size is for our supercharger shafts, but I'm going to contact Alta about this. I ran the pulley for about a year and a half before things went completely awry. The taper-fit coupler just doesn't hold the pulley in place well enough. Hopefully the newer clamp-style pulley will work (Alta claims it will work with shafts that have been worn down by as much as .020", or .55mm), otherwise, I may have to rebuild my supercharger.

 

Surprising the car did not run very hot...no sc boost, no waterpump....
Congratulations on finding the issue!!

 

I didn't drive the car very long after it cut into limp mode that fateful night. I probably limped it home another mile and a half back to my apartment. After that, I just drove it onto the trailer and up my driveway, and ran it up and down the street once after I did the bypass valve and throttle body..

I just hope this new pulley works ...

 

Just be sure to use some locktight and a tourqe wrench on the install...
Atleast the install of the new pulley is simpler than the orgional!!

 

New pulley has been ordered.

Jeff at Alta was a great help. Upon his advice, it was confirmed that the shaft wasn't worn down enough to prevent using the newer, clamp-style shaft coupler. I was also advised to put some red Loctite on the supercharger shaft when installing the new 17% reduction pulley to prevent this from happening again.

Outlook is good, hopefully I can get the car running this weekend so I don't have to keep driving my parents' Honda Pilot.

 

Good luck.

 

Thanks. If it slips again, I'm going to have to lay a few spot welds on the pulley coupler/SC shaft to keep it in place. I really hope it doesn't come to that, though.

 

Had that same type of pulley fail on me, although it was a Craven Speed pulley. I just ended up replacing it with the Alta v2.0 pulley (internal clamp style) and I even added a small coat of JB Weld to it to ensure it never slips again!

I am having a different issue though that I believe to be the throttle body. I think the spring inside it might be wearing out. When I'm giving my MINI a little bit of throttle (27-30 on the ScanGauge), you can hear it fluttering. The TPS shows steady, although you can hear it fluttering, and you can feel it when you give it about 50-75% throttle in higher RPM's (between 50-70 on the ScanGauge). It sounds like a bird chirping due to the fluttering so much in the 27-30 range, and the whole car jerks like it's cutting out while I'm accelerating at 50-75% throttle. Although, at 30-50 or WOT, you don't hear anything unusual and the car doesn't jerk. Also, the reading of the boost (or vacuum) on the ScanGauge will also reflect what I'm hearing and feeling. I originally thought it was the bypass valve, but I replaced that and it did absolutely nothing. It will not replicate this unless you are driving the car, and is more noticeable while under load (like a hill, etc). I checked for vacuum leaks but I didn't see anything. I replaced the IC boots, and that didn't fix it either. I checked the IC for cracks, but it's perfectly fine. I replaced the crank shaft pulley (as mine just failed on my way down to MOTD this year), and that made no difference. All the other pulleys had been checked during that time as well and they are perfectly fine. It's been slowly getting worse for the past couple years, and after each MOTD it seems to only be getting worse. Has anyone every tried disassembling the throttle body? I am NOT getting a single code from it, and the ScanGauge does not show a flux in the TPS so I don't believe it to be an issue with the sensor or the wires/connector. That would normally cause a code to pop up, or would be reflected in the TPS reading on the ScanGauge. Again, it does show the boost going up and down (about 1-3psi depending on the TPS). This has been getting progressively worse after each MOTD and has started right after MOTD 2011. Can anyone shed any light on this problem? I will try making a video on my way home tonight and uploading it for everyone to see.

 

Unfortunately, I don't think we can disassemble our throttle bodies. While I wish we were back in the good 'ol days of a cable-actuated throttle, our "futuristic, state-of-the-art" eThrottles are basically throw-away items.

I had the same symptoms as you - some light yo-yo under partial throttle on the highway in 6th gear.

Check this thread out. I tested my throttle body and found a bad potentiometer on one of the pins.

Oh, how I wish someone would make an "analog" throttle body and cable setup for our cars ...

 

I am having the same fault code appear after going into limp mode when I try to accelerate with the air conditioner on. Was 3 hours from home when I went into limp mode. Belt squeal, burning smell, and no boost. Made it home and looked in the engine bay and saw a grease or oil residue on passenger side of the engine bay. Put the car up on jack stands to look at the crank pulley(read it was most likely the culprit) found tons of oil all in the passenger wheel well and all over control arms and tie rod. Would the oil leak be caused by the crank pulley issue?

 

@flipguy I just had the same issue with my R53 and took it down to the dealer they are saying it is my Harmonic balancer and that it has fallen apart.