1999 bmw z3 2.5 M52

[nicolevin14]

please help 1999 bmw z3 2.5 M52
Misfired on 1,2,3 with pending P0301, 302, 303


Valve cover was leaking, Replaced valve cover and gaskets and installed 6 new spark plugs, tested ignition coils and replaced 1 faulty coil in #6.


Tested compression and read 185-190psi around the board.


After new valve cover And gaskets, 6 new spark plugs, 1 new ignitioncoil and oil change I started car and noticed vacuum leak from intake boots.


I replaced the intake boots aswell as the entire pc/ccv system(replacing throttle body o ring, oil dipstick o ring and air distribution system o ring's.


I smoke tested into the intake boots and did not find any leaks, aswell as into crankcase via oil cap hole and did not find any leaks.


Ive disconnected my MAF sensor to see if car will smooth out but vehicle still misses hard with


MAF unplugged.


7/11/25 | replaced pcv/cv and ran the vehicle and was given misses on cylinders 4,5,6.


Pending codes read, Po304,305,306 and P1189, I have cleared a couple times after small repairs and the misses will differentiate from cylinders 1,2,3 and 4,5,6 but always stay on one bank either 1,2,3 or 4,5,6. 7/12/25 I ran car to check codes and was given P1188,P0173, Po301,302,303 (misses on 1,2,3),


7/13/25 l retested compression and checked plugs and ignition coils again everything seemed good. 190 psi on all 6 cylinders aswell as put smoke into intake boots and crankcase again and did not visually inspect any leaks.


Parts that have been replaced:
Valve cover+ gaskets
Spark plugs
pcv/ccv valve and hoses
Oil dipstick o ring
Throttle body o ring
Air distribution piece o rings
Intake boots.
Oil change

All parts replaced from fcpeuro

 

[Shelly]

 

[ChrisD]

It seems as though you’ve gone through a fair bit of diagnostic work and picked up a few issues related to spark and air. Assuming you’re happy with your work to date, I think you need to look at potential issues with fuel delivery. As your issue appears to be across multiple cylinders then maybe look at fuel pressure for your next diagnostic path. At the same time, check over your wiring, particularly earth connections as you have an issue that is seriously affecting how your engine is running.
Good luck with getting to the bottom of it.

 

[Mint]

Hi and to the forum from me too in Stafford. Hope you can get to the bottom of your problem soon.