Engine playing up…. 1 week to SVA…. Damn!

[alackofspeed]

Dear all,

As sods law would have it, 1 week prior to my SVA my engine has decided to start playing up – manifesting as a miss-fire.

I’ve been pretty thorough checking for faults, and I haven’t yet solved the problem.

The miss-fire isn’t bad, just a slightly lumpy idle, and minor occasional pops when holding the revs at “fast idle” (circa 2k rpm).

I’ve checked the following so far:

Plugs – look perfectly healthy – no fouling with oil, fuel, or carbon.
Engine coolant temp – ECU shows a sensible reading of ~ 80 Celsius.
Inlet air temp – was registering ~ 8 Celsius yesterday afternoon.
Cam & Crank sensor fine.
Lambda – 12v (actually 13.5v…) supply to heater is fine, and the output appears to be swinging merrily.
Fuel pressure – dead on 50 psi, with no fluctuations.
MAP sensor – sensible vacuum figures for idle.

The only slightly quirky figure I can see from the ECU logs, is the closed loop short term fuel trim, which is at about -7%. My suspicion is that this is causing the engine to run a bit lean, causing the miss-fires. If the fuel trim is the issue, then the only culpable sensor is the lambda sensor.

As a “time is running out” measure I’m going to bung a new lambda on this evening, and hope that remedies the situation. However, in case it doesn’t I’m wondering if there’s anything I might have overlooked….? Can anyone think of something I’ve missed?

Cheers,

John.