540i Awful misfires

[tfe.39]

96 NV, car runs fine on a cold start for 5 or so minutes if driven moderately then develops an awful misfire or few. Sometimes sounds like a tractor under slight acceleration and complete loss of power unless you put your foot to the floor. Battery voltage drops to as low as 12.7 when you blip the throttle but alternator reads from 13.5 to 14.1.

Have an OBD1 port and reads o2 sensors however the cables have been burnt through on the car so can’t guarantee the harness is any good. Ran fine even when it was burnt through.

Thanks for any help.

[JimLev]

Probably vacuum leaks, get a smoke test done to find them.

[BimmerBreaker]

Turn the car off, unplug the MAF and restart it next time this issue occurs - if it drives better, almost certain to be vaccuum leaks of some sort.

The car runs open loop during cold starts, essentially ignoring the data from MAF and O2 sensors. Once nearer operating temperature it switches to closed loop operation where it looks at MAF and O2's. If you have large vacuum leaks, it can run ok in open loop but then run poorly in closed loop.

[MtnGn]

Mine turned out to be degraded knock sensors... only took a couple of years and a WHOLE bunch of replaced parts, vacuum leak tests, etc. to chase down. Car runs like a champ now. I love to drive it.

good luck