P16a7 - 2006 z4mr

[MadGus]

Hi folks… posting up my first head-scratcher with my “new to me” car.

With the engine fully warmed up, at highway speed, downshift into 4th and holding on the accelerator at WOT for ~4 seconds or so triggers this code, along with limp mode, the yellow EML light, yellow DSC/traction light and yellow BRAKE light.

I am running Megan racing headers (catless), a tune from Severn (pokeybritches), and an aFE cold air intake.

Troubleshooting to date includes:

Replacement of the two throttle position sensors on the engine (swapped one at a time and tested both on multimeter) - both were good
Replacement of the throttle actuator - original was good
Replacement of the MAF - original was good
Continuity check for the MAF to DME wiring - wiring was good

The error details from INPA and ISTA talk about the MAF reporting ~200mg/stk less than the calculated amount of airflow, and this makes me doubt that the throttle position sensor on the gas pedal would be causing the problem.

Sooooo… that leads me to a partially clogged exhaust. I’m already running catless headers, so that would mean the H-pipe main cats could be clogged ($1800 to replace with manufactured ones from the online stores), the resonator in the X-pipe could be clogged, or the mufflers could be clogged.

Question for the forum is: am I missing anything else that I should be thinking about in the troubleshooting?

Data logs of the airflow (g/s) max out at 160 and never drop to 0… limp mode seems to be triggered around 4800rpm every time.

I’m going to drop the exhaust this weekend and inspect the components with a camera snake… hopefully the problem will be visually evident!

[TRiCC]

Try replacement of the Throttle Position Sensor on the front of the throttle actuator rail, above the oil filter housing. I had this exact problem, replacement of this part with a OEM part fixed it, this was three years ago, havent had a problem with those three lights since, as a suggestion. Good luck!

[MadGus]

Thanks, but I already tried replacing both of them without any success.

[MadGus]

Dropped the exhaust and separated the S/H-pipe with cats from the x-pipe and scoped both with a tiny camera. There's no ratting when I shake either piece, and visibly all four ends of the cats look intact and unclogged. The x-pipe is totally clear, and I can snake the camera through both sides of the entire length of that section.

I also scoped the mufflers, and while the turns inside are too tight for my camera to go all the way through, they look clear from both sides and also don't make any noise when shaken.

Sooooooo...

I'm going to reinstall the exhaust in the morning, and try replacing the accelerator pedal with a factory one that came today... which has the third and final throttle position sensor for the car in it.

If that still throws a code, then I'll use this $32 backpressure gauge that I got from amazon and see what it says. If the backpressure test comes back good, then I guess I'll go back to the stock tune and see if that changes anything.

Open to any other suggestions as well!

[MadGus]

No joy with the exhaust put back on, so I swapped the accelerator pedal and again still getting the code and limp mode.

I can run the engine way above this rpm and vehicle speed in 3rd with no problem… just seems to constantly throw code in 4th.

I attached the freeze frame data from OBDFusion. 49% throttle position doesn’t seem possible with the accelerator floored. That’s confusing to me… might have to look at resetting adaptations, but I thought our cars did that automatically at startup??

Might do the back pressure test later this afternoon, just to confirm what I was inspected with the exhaust taken apart.