Hello,
The idle bogs low then bounces back on closed loop fuelling only. The short term fuel trim gets more negative, then the engine bogs, STFT resets to zero, and idle steadies again. This cycle repeats. I've noticed the spark advance also fluctuates but I'm not sure if this is in response to keep the engine from cutting out, or if it causing the bad idle.
The car also occasionally has a random misfire on light throttle opening.
When cruising I've noticed that the STFT can sometimes fluctuate wildly and at other times stick at a fixed -20% due to the O2 voltagqe flat-lining at 0.9V.
What I've tried:
- Fitted plugs.
- Checked spark leads resistance, appears in spec.
- Checked coil packs resistance, appears in spec.
- Fitted a new lambda sensor.
- Tried a replacement idle air control valve.
- Can't find a vacuum leak but do not have a smoke machine.
- The fuel pressure regulator does not seem to be leaking.
- Cylinder compression seemed consistent.
As the fuel trims never settle at idle I'm thinking it might be an obvious symptom of something...? The engine is MAP controlled with no MAF sensor.
I'm thinking it might be fuel related. I'm due to check fuel pressure once I have the right fitting arrive. Other than that, perhaps a malfunctioning injector.
Video of the problem at idle:
