Rough idle, no acceleration until STFTs go to max.

[submerged]

My 1999 Z3 2.5L sat for 6 years after the previous owners put in a replacement engine which I'm told did run.
It will start and rev smoothly to 1500-2000 rpm and then it acts like its starving for fuel and wont idle nor accelerate.
If I continuously romp on the pedal for a couple minutes the STFTs will increase from 0 to 27.3% and then idle and run.
LTFTs are at 0%. They started at .7 and 1.5 but after 60 miles they are at 0 and have not changed.
Shutting engine off normally results in same rough idle and no acceleration once again.

* At the moment, No error for DME Engine-throttle output-stage shutoff after diagnostic.
Only codes returned after 5 min of running:

• P1188, P1189 for short term fuel trims at max
• P0150, P0130 for upstream O2 sensor readings too low.

The following has been done with no improvement:
Old gas purged
New fuel pump, fuel filter, fuel pressure regulator. At the rail she reads 50psi and delivers 16oz of fuel from the rail in 15 seconds.
Spark plugs cleaned
New CCV and hoses (wheeze from torn diaphragm is gone)
New Air intake boots
New MAF sensor
Throttle body cleaned including pedal position resistors
New idle control valve
(4) New O2 sensors
New vacuum lines to 1 way valve, secondary air pump, and pressure regulator
(6) New injectors,
Awaiting (6) new ignition coils

Diagnostic results:
All cylinders have 150psi compression. When kept running it will throw codes for miss-fire in all cylinders.
No response to spraying intake, hoses, etc. with carb cleaner.
Smoke test showed no air leaks.
DISA valve does not hold vacuum for more than 3-4 seconds but does move as idle gets rough.
12V at injector rail is good. (11.5V with 7Amp load)
Plugs came out black again after 60 miles of test driving.

Other notes:
Repaired ABS module, installed new front wheel speed sensors, and wear indicator.
TB was giving codes for stuck throttle and pedal position sensors but not now.
Secondary air pump does run at startup.
Entire car was underwater at some time before 6 years ago.

Prying Questions:
Why are LTFTs not updating? It sure seems that would help with restarting.
Other than brake booster, CCV or external leaks what other system could cause unmetered air to enter combustion chamber?

 

[jaguartvr]

I had the same symptoms on my Z3 that had stood a while, turned out to be a stuck throttle flap.

 

[NZ00Z3]

From your codes, it looks like you have a M52TUB25 engine? Is that correct?

You talk about lean conditions, but have black plugs, which is a rich condition sign? Yet the STFT head out to 27% lean?

The M52TU DME does not distinguish between lean/rich mixtures in the codes. It just says that it is outside of acceptable limits. You then have to look at fuel trims under set conditions to see what the situation is. These are usually hot idle and steady highway cruise.

Suggested work
It looks like you have problems with your O2 sensor signals. The mixture problems are a result of the pre-cat O2 signals.

• First off you have confirm if the pre-cat O2 sensors are working. With the engine in closed loop control (hot engine), check that the live data Pre-Cat O2 signals are switching between 0.1 to 0.8V for both banks.
• The Post-Cat O2 sensor signals should be stable somewhere above 0.5V. If they are switching like the pre-cat O2 sensors, then this is a sign of blocked/struggling Cat's. If they are flat lined somewhere below 0.5V, then you either have stuffed sensors/bad connections, blocked cats, or a mixture that is so lean that it is being reflected onto the post cat O2 sensors.
• If you have good sensor signals, check that the pre-cat sensors are plugged in the correct way around. Un-plug one while watching the live data signal and see if the correct signal flat lines.
• If the post-cat signal are showing blocked/struggling cats, then remove the pre-cat O2 sensors from the exhaust and go for a drive. If the problem is fixed, then you have blocked cats. The engine will be very loud, like a tank/tractor, so watch out for cops.
• As the whole car has been underwater, you've got lots of potential issues. One to check is the DME connections. Remove the DME connections and inspect for signs of water, coolant or oil contamination. Especially Connectors X60002 and X60003. X60002 is number 2 counting from the fire wall to the bumper. It has the O2 sensor wiring. X60003 is number 3 counting from the firewall to the bumper, this has lots of engine signals and controls that when there are contaminated pins, causes all sort of issues.
• The M52TU MKD throttle body will follow the pedal signal with the key in position 2 and the engine is off. Remove the air induction boots, so you can see the throttle plate. Turn the accelerator cable cam by hand and the throttle plate should follow. If you are concerned about the MKD then read this thread: https://zroadster.org/resources/how-to-clean-a-mdk-m52tu-throttle-bodys-potentiometers.47/
• What make of MAF did you purchase. This is important, as many aftermarket MAF's are not of good quality. The Siemens/VDO MAF is the one to get.

That's enough for now. Let us know how you get on.

If you are really stuck, purchase the smart device app, OBD Fusion and the associated EML327 OBD2 adapter. It's a cheap set up that will let you log live data. There are some standard tests that can be run that collects the data needed to do a full analysis of your engine. I do this type of analysis all the time on the E46 forums, so can have a look at the data and tell you what I see. Read more about OBD Fusion here: https://www.e46fanatics.com/threads/obd-fusion.1240733/#post-18380161

 

[submerged]

Thank you for your reply,

I re-installed the new MAF sensor and it now idles and accelerates much better.
O2 signals are no longer railed at 0V, are acting normal and codes for O2 and fuel trims are gone.
I had at least 3-4 concurrent issues :

• Defective MAF sensor
• Idle air control valve was not fully closing (replaced)
• Throttle plate was/is sticking
• One of the two pedal position resistors is jittering when moved.

The TB issues continue to cause random EML and shutdown but a replacement is on its way.

Brent in Big D.