Customer reported poor running.
Fault codes recorded for lambda sensor heater circuits Cam sensor P0340 among others.
As I was getting multiple sensor faults I have had ECU problems in the past giving these symptoms so I sent the ECU to Ecu Testing. When returned I could clear all codes except the P0340. Deeper investigation showed the cams were incorrectly timed (i.e. on the incorrect crank timing detent).
I re-timed the engine expecting an end to the problems, no chance, the engine still hunts at idle.
Questioning the customer, they said they had only had the car a couple of weeks before bringing it to me so I have no history. So far I can see newish lambda sensors, MAF, CMP and a broken cam cover bolt as well as the mis-timing issue.
I have smoke tested with no leaks found (I suspected a sticking EGR valve) which I eventually removed to physically check it, no problems found with it.
I removed the upstream lambda sensor, checked the cat had not collapsed and ran the engine with the sensor out in case the exhaust was blocked.
The ECU software has been updated to the latest issue.
All this made absolutely no difference to the hunting.
The compressions were measured at 190, 195, 195, 200 psi.
At idle the the manifold vacuum is poor at 56 kPa and I suspect this is why it hunts, what I can't find is the reason why. To me this would point to the cam timing but I have re-done it several times.
Another possibility could be sticky valves as I'm led to believe that is a common problem, but would it give these symptoms?
Could it be wrong oil grade affecting the hydraulic tappets?
Any ideas?
Shaun