New Engine Management Computer??

[Nordgeist]

So I've been having numerous issues with my 06' Z4M for about 10 months now. The engine will randomly die every once in a while as I'm driving; it also suddenly surges forward as you're accelerating. You'll have your foot about 30% on the throttle, just normal driving, and suddenly it'll lunge forward like you just floored it. Also at idle, the rev counter bounces around under 1K RPMs and the car shudders and shakes like it's about to stall. Finally, it's been throwing up a "Check Engine" light that reads as a failed Mass Air Sensor. But that's been replaced twice now, and it still comes up bad.

My mechanic read the engine codes and has done some testing, including sending out the codes to specialists to diagnose. All signs point to a bad engine management computer, but apparently that's about $2,000 to replace.

Any thoughts, suggestions, ideas? I love the car but that's a hard pill to swallow.

[WeekendWarriorz]

Who's your mechanic in SD? Try getting a second opinion from another shop. It's very possible that a mouse or rat has crawled into your engine bay and maybe chewed up one of the wires, as what you describe is similar to a bad electrical connection. I'd have the car thoroughly inspected before dropping good money on a ECU.

[GuidoK]

Without all the specific INPA codes&descriptions present no one can say anything sensible about this imho.

[mattfwalters]

This sounds 1,000% like a grounding issue. Definitely check that out before anything else. I would specifically check three of them:

1. The engine ground strap - the thick brown wire on the (US) passenger side bottom of the engine just in front of the front crossmember;
2. The ECU's main grounding point, which is a single thick cable that terminates on an M10 stud on the firewall just in front of the (US) driver's side wiper; and
3. The throttle pedal's main grounding point, which is one of those weirdo gang grounds with a bunch of little brown wires on one side and a metal heatsink-looking mount. It is in the (US) driver's side footwell a little bit forward of the pedals and on the inside of the fender.

That being said, I just pulled a perfectly good DME from my '06 Z4M that will not be going back into it, so if you actually do need to replace yours PM me and we can work something out.

[StickMon]

Might want to swap out the throttle position sensors.
I've had similar symptoms. I'm now on my third set.
But then I'm close to 190k miles.

[Azeka1]

Perhaps there is someone local with an M that can swap ECUs to see if it is the problem? Maybe your local specialist knows someone?

[mattfwalters]

Originally Posted by StickMon

Might want to swap out the throttle position sensors.
I've had similar symptoms. I'm now on my third set.
But then I'm close to 190k miles.

Did your dead / dying TPSes cause idle issues? I would have thought that any time the DME thought the car was entering an idle condition (i.e. throttle pedal below some value + RPM below some value) it would switch to the IAC valve to control RPM rather than caring about the actual throttle plate position. If the TPS(es) weren't showing the throttle plates full-closed after DME commanded them closed I would expect an error specific to that. The crappy idle, throttle surge, and MAF codes suggest to me that several sensors / motors are malfunctioning at the same time.

This perspective may be affected by the fact that I've just rewired every sensor and driver on my car's engine and have been digging into idle logic in the Infinity.

[StickMon]

The first TPS I had fail developed an intermittent open near the idle position.
Cruise was fine. Idle was all over the place and then it began starting into limp mode.
Only #1 was bad, but I replaced both.
3 months later it sputtered and surged a few times, then I got yellow brake, tire pressure, and DSC lights. It went into a strange mode where it ran smooth, but a little down on power, and with delayed deceleration.
Code was TPS #1, so I put the good old sensor in and it was fine for over a year.
Two weeks ago got the same sputter, then the yellow brake, tire pressure, and DSC lights. Same strange mode with delayed deceleration.
No code with Peake Research or INPA.
Replaced #1 with a new one. No joy. Replaced #2 and now it's fine again.

The first failed TPS measured obviously bad with an ohmmeter.
Couldn't find a problem with the second set, either with an ohmmeter or with INPA.
The car just didn't like them. Rejected the first one after three months, and the second after a year and a half.

[Nordgeist]

Originally Posted by mattfwalters

This sounds 1,000% like a grounding issue. Definitely check that out before anything else. I would specifically check three of them:

1. The engine ground strap - the thick brown wire on the (US) passenger side bottom of the engine just in front of the front crossmember;
2. The ECU's main grounding point, which is a single thick cable that terminates on an M10 stud on the firewall just in front of the (US) driver's side wiper; and
3. The throttle pedal's main grounding point, which is one of those weirdo gang grounds with a bunch of little brown wires on one side and a metal heatsink-looking mount. It is in the (US) driver's side footwell a little bit forward of the pedals and on the inside of the fender.

That being said, I just pulled a perfectly good DME from my '06 Z4M that will not be going back into it, so if you actually do need to replace yours PM me and we can work something out.

Sent you a message, thanks!

And Azeka, that's a really good idea, I'll check. He's a BMW specialist so he should have something lying around we can test.

The other thing I forgot to mention is that the computer log shows that it was reset three times before I bought the car. So my mechanic believes this has been an issue for a long time, and they were tinkering around with it before selling the car. Who knows, but there's something funny going on in the logs in any case.

On another note, how long are these engines good for? I'm at 99k miles right now, what's the life on Z4Ms? Does anyone know? I'm just wondering how much I should invest in keeping the car going if more and more serious issues are going to keep popping up like this down the road.

I thought the S54 was supposed to be bullet proof, but I've had a lot of issues with mine from day 1, so it's making me wonder, but maybe I had bad luck.

[StickMon]

I'm close to 190k miles, and all the whirly bits are rock solid.
Just the occasional electrical gremlin.
Fly-by-wire throttle is really fussy. It's the first thing that will report failure if your battery gets a little low.