Engine Idle post MAF refit

[Shootetm]

I recommissioned my 993 varioram in April after it's winter storage and have had a misfire since starting using in May, what I've done to rectify is outlined below and the current issue is that having just replaced the MAF the car now starts fine and appears to have no misfire (great that seems solved) but the car has a 80% chance of stalling at junctions once I depress clutch. I have read that the ECU takes time to remap to a new MAF, is this correct and how long should I expect this to take (miles / engine on time?)?

Timeline
Oct 22 - Put in garage after 993 event to Northway Porsche
Winter - cleaned various engine ancillaries (which I think also included MAF plastic and maybe damaged MAF sensor?)
June - Full service including spark plug change at Tognola who suggested ignition leads may need replacing
June - Almost emptied tank and half filled with Exxon 99 Supreme (still misfire)
June - Replaced ignition leads, then dizzys and rotors and then coil (still misfire)
July - Tested air intake temp (has ohms in range)
July - Replaced MAF with OE Match replacement from Design 911 (misfire has gone and idles ok when cold but once warmed revs drop too low and stall occurs)

I have rationalised that if MAF was reading high (less air going in engine than the MAF was measuring), then ECU was putting in too much fuel and hence the occasional misfire and pop bang in exhaust that ECU was trying to adjust for. Now a new MAF has gone in (correctly reading) the ECU thinks its getting more air than it actually is and hence running out of oxygen for combustion and stalling). Not sure if my synopsis is correct so looking for guidance....thanks. Will ECU recalibrate and how long will it take/can I reset to factory? I don't have an OBD reader.

 

[BarryN]

Not sure 100% but disconnect the battery and see if that allows it to reset.


I would also remove and clean the idle control valve.
It should move freely when you shake it, (rattle)

 

[Shootetm]

Barry - The car idled fine before I swapped the MAF, and because the issue was a misfire I have assumed the idle valve is ok but you could be right that now the MAF is new it's highlighting that other components are not working as well as they should. I have disconnected the battery for about an hour, reconnected and restarted and it's still the same.

 

[BarryN]

Sorry, slow response, I don’t check in here often.
One hour should have done it, then a drive to let the car recalibrate.


I would still clean the ICV also double check that everything is seated correctly after changing the MAF.


Christian Sanger would be my next port of call.

 

[Shootetm]

Barry - thanks for feedback.

I have cleaned the ICV, and bought a German sourced non-OEM version as a test - put both in and idle issue still remained in both so summarised that the original is fine. I swapped the original Bosch MAF back in, with original ICV and the idle stall has disappeared. The misfire still exists but does seem less than previously observed, it occurs when cold and hot so assuming not O2 sensor related. I need to take it for a decent drive to see if it's just a lack of use gremlin.

I have also had a couple of calls with Christian, very helpful, and he strongly suggested not to trust the "cheap" non OEM options (which I agree with but couldn't source a Bosch MAF. I think he and I have both concluded it needs to be hooked up to an OBD and have the eyes of an expert rather than a DIYer!