Service Engine Soon - Tired of Chasing it

[jhawk19]

I purchased my 2004 BMW Z4 (e85) two months ago. The car had brand new hoses and lines installed as well as a new A/C and radiator when I purchased it. Since then, my Service Engine Soon light came on. I figured it was NOT a vacuum leak b/c the lines are new. I've checked the intake boot (brand new), no leaks. I used the Autel 500 scanner and saw misfire codes for cylinders 3 and 5. I replaced all the plugs with Laser Iridium plugs by NGK. Didn't fix. I replaced the coil packs and valve cover gasket. Didn't fix. I replaced the DISA valve. Didn't fix. I can clear the codes and ride around, but within 24 hours the Service Engine Soon light is back on. The car drives great. The car sounds great. It has rough idle upon cold start, but after it warms up, it's perfect. Monitoring systems with the scan tool has the idle steady at 675 - 715 RPMs.

The misfire is jumping or I get multiple misfire codes, so it's not isolated to 3 & 5 only. What is wrong?!?! What can I check or replace next? Wouldn't I get a code for O2 sensors or injectors if they were the problem?

[Steeler]

Misfire can be caused by lean or rich condition, which can point to a dirty or faulty injector.
Also incorrect fuel trims reported from faulty O2 sensors will also cause misfires.

[jhawk19]

Originally Posted by dbarton62

Misfire can be caused by lean or rich condition, which can point to a dirty or faulty injector.

So, that was the original code (P0170 & 0174). Based on that I checked for vacuum leaks, then changed the plugs and valve cover gasket. That's when the misfires appeared. Once those appeared, I changed the coils and DISA and I poured some injector cleaner in the gas tank. I'll probably do that again when I fill up next time.

[Steeler]

Originally Posted by jhawk19

So, that was the original code (P0170 & 0174). Based on that I checked for vacuum leaks, then changed the plugs and valve cover gasket. That's when the misfires appeared. Once those appeared, I changed the coils and DISA and I poured some injector cleaner in the gas tank. I'll probably do that again when I fill up next time.

If you can afford to have the car down for a period of time, cleaning and flow testing the injectors is reasonable price wise.

[drocket77]

I am in the same boat as you. https://www.zpost.com/forums/showthread.php?t=1685431

Once i "fixed" all of the obvious stuff, I am now getting O2 errors. I am running cats, but all the o2 sensors are pre cat, with anti-foulers on the #2 sensors. I scheduled an appt for next week to have the placed post cat to see if this will fix it. I would suggest replacing the O2 sensors, as they are fairly easy and not to expensive. Or hook up INPA and you can see the O2 values.

[pokeybritches]

How old is your MAF sensor? MAF and O2 sensors are wear items. You can also try data logging to see what different parameters are doing, like STFT, LTFT, MAF, and so on.