Z4 3.0Si (E86) - Poor running

B

Birr97

Member
Hi all,

Hoping to get some advice for my Z4.
It's been running poorly ever since it had a blast from South Wales to North Wales and back around mid August this year.

The issues are:
Surging/jerking between 1100 and 2800rpm, mostly on light throttle.
Revs bounce/jerking when off throttle and engine braking, exhaust burbling and spitting more than usual.
Feels flat/low on power through above rev range at full throttle, but doesn't seem to surge.
Rough idle (Closed and Open loop).
Strong smell of fuel from exhaust (especially on cold start).
Lower MPG than usual (approx. 5 MPG lower).

Revs bounce when throttle stabbed (revs drop slightly then rise).
Revs bounce on upshift (when engine revs drop down to match wheel/gearbox speed).

What I've tried/checked:

  • Replaced MAF
  • Unplugged MAF - driven and at idle - runs the same (poorly).
  • Unplugged MAP at idle, ran a bit worse but not much difference.
  • Swapped over pre cat O2 sensor leads, idled even worse (barely and terribly) and threw codes for swapped plugs.
  • Unplugged Eccentric Shaft Sensor - Disabled valvetronic, drove around just using the throttle body, same issues (surging, revs bouncing) with less power and laggy response (due to no valvetronic).
  • Swapped to another set of ignition coils I had, no change
  • No oil in ESS sensor socket or around seal.
  • Oil cap slight vaccum when opened, revs dip then recover and idles as it was with closed cap.
  • Sprayed brake cleaner around possible air leak zones (intake manifold gasket, CCV, CCV hoses and right around rocker cover where it meets the head with no change.
  • Eccentric Shaft Sensor was replaced 3000 miles/1 year ago when I replaced the rocker cover gasket.

It wasn't giving me codes (other than when a sensor was unplugged etc but I cleared), I have checked tonight and I now have the following:
2C7F: Lambda Control 2
2C2B: Oxygen Sensor Before CAT: System Check
2C2C: Oxygen Sensor 2 Before CAT: System Check
2C6C Oxygen Sensor 2 After CAT: System Check

Unfortunately my laptop with INPA/ISTA has died so I can't take logs while it's running.
I have checked some values while running with a Creator C501 diagnostic (smooth running, o2 sensor voltages and mixture adaptation) and have attached some videos below.

Cold start behavior and some figures

Closed loop idle behavior and figures

I want to be hopeful and say it's just the oxygen sensors, but they were replaced roughly 6000 miles/2 years ago.
Apologies for the wall of text, if anyone could help make sense of this it would be greatly appreciated!
 
Last edited:
Do you know what make of sensor was used. Bosch are OEM and the recommended ones. There are a lot of cheaper makes out there to avoid, including universal ones where the leads are cut to splice in replacements. Establish this and yes you might have duff cheapo sensors
 
Mike6 said:
Do you know what make of sensor was used. Bosch are OEM and the recommended ones. There are a lot of cheaper makes out there to avoid, including universal ones where the leads are cut to splice in replacements. Establish this and yes you might have duff cheapo sensors
Click to expand...
Bosch sensors from Autodoc, they were specifically for BMW (had the correct plugs).
 
Just to update this.

Found an air leak where the air intake meets the throttle body using a smoke tester, tightened the clamp so that was sorted.
The exhaust was also blowing just after the bank 2 cat on the join where it meets the downpipe, new set of gaskets and that was sorted.

Reset all adaptations via INPA.

It now sounds sounds and goes much better, but there's still a rough idle.

Edit: Now sold as I recently bought a house and I have to prioritise that unfortunately.
Probably underpriced it at £3700 but it's giving someone the chance to diagnose and swap parts with a bit of float.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom