Electrical issue causing occasional misfire. Help!

[jeffbebe]

That's because you deleted the adaptations (the early DME's lost all learned values when the battery was disconnected) - and it will take a time to re-learn. That's why diagnostics can be so useful if you can find what the adaptations are as it would point to where the default values are lacking.

Thanks Tim. I figured as much re: adaptions but was confused by the fact it seems to run significantly better after the initial surges although it could still be a variety of causes.

So as it warms up? Have you checked temp sensor values using diagnostics from a cold start? also check the oxygen sensor values from cold start.

Diagnostics not working currently. This is the first problem since i took ownership 3-4 years ago that I haven't been able to diagnose through traditional methods! Will spend some time over the next couple of weeks finally trying to find the faulty module causing diagnostics not to work and then hopefully I'll be able to solve this annoying puzzle.

[jeffbebe]

Checked the o2 sensors this weekend and the clip on the right hand bank sensor had snapped and the wire was hanging down enough to get pretty chewed up with an obvious short. I had a spare sensor so swapped it out and the car ran beautifully! Still seems to have the surge at idle so there is another issue that I need to identify but (touch wood) the replacement sensor seems to have eliminated the misfire.

Now need to get to the bottom of the hvac issues. Compressor was recently reconditioned and no other refrigerant leaks but it has stopped blowing cold. In fact, it seems to blow hotter than the outside air but that is speculative. Heater valves seem to be working as the hot air works and I can hear them clicking away when the temp is set to max. Have had a good read of this thread: https://www.bimmerforums.com/forum/s...-Control-Valve - and based on this I think the most likely culprits are either a) the hvac control unit is faulty and not closing the heater valve or not engaging the compressor, or b) the reconditioned compressor has crapped out already and the clutch is not engaging properly <-- I can't hear it clicking when I turn on the a/c so this seems the most likely cause.

Of course, all sorts of other electrical issues have begun occurring so it's possible it's something else entirely! Will test the clutch properly this weekend. Still really warm here in NZ so would like to get it fixed!!

[jeffbebe]

The saga continues but I'm getting closer to resolution. Finally managed to stomp test in the absence of functioning diagnostics. I discovered that the check engine light was not malfunctioning after all but that the PO had got some black tape on the inside of the cluster through the light bulb slot to cover the check engine light! Presumably, either to dupe me when I purchased (it was running pretty rough when I bought it) or to get it through a Warrant Of Fitness (NZ MOT).

Anyway, removed that, replaced the bulb and managed to get read the fault codes. Only one fault on Bank 1 - 1222 - Oxy sensor. Since the O2 sensors are brand new (see previous post), I can safely rule out a faulty sensor, leaving me with the following likely causes:

1) HT fault (plugs, wires, caps, rotors, coils)
2) Vac leak
3) Injector spray pattern

No standout option as I have recently replaced the entire ignition system, have performed a leak down test with no visible leaks and recently serviced the injectors. I guess it's possible one of the injectors as got partially blocked which might explain why the fault is inconsistent.

Presuming bank 1 refers to cylinders 1-6 (LHS as you look at the car). Will take a good look at HT connections, plugs and injectors.

[Dr. T]

What about also checking the O2 sensor wiring/connector condition/integrity?

[jeffbebe]

What about also checking the O2 sensor wiring/connector condition/integrity?

Both are brand new. The old one had a short so I replaced but issue remains (though not as bad).