possible maf sensor problem or not?

[skipjack]

My car has had a wierd issue for some time now like this: it runs perfectly and then occasionally after stopping and turning the engine off, etc at the supermarket, I come back start her up no problem, apply throttle and she dies but not necassarily stalls. I can drive by tickling the throttle pedal and gradually increasing speed and then a short time after it starts to run perfectly again. If I apply a lot of throttle and it does not die she will speed up to about 1750 rpm and then cough and try to cut out if I do not catch it.
However the time for it to correct itself varies from a few seconds to 10 mins or not at all . I was unable to get it to clear a little while ago until after a few days I started her up and it was fine. The trouble is if I take it to a garage there is no fault. I have had all the leads changed, all the filters changed etc etc trying to cure it.

She has now failed on emissions and for the first time is showing a fault on the MAF sensor. But she is still running ok. Does anyone know if these 2 problems are probably related . She always fails on emissions initially but this time my bloke at the garage reckons it is different. Apparently they have checked the connections so that easy option would appear to be out.

As the cheapest (or only), MAF sensor I have found is at Camskill for £500 approx, does any one have one around or know where I might find one a bit easier on the wallet

[elnevio]

Ah-ha, my favourite Winning Turquoise VR-4!

Initial thought was that the stepper motor could need cleaning. Coolant temperature sensor failing is also a possibility.

You should be able to get hold of a cheap second-hand MAF on here, I would have thought. If I was nearer, I'd let you borrow mine to help with the diagnosis.

[skipjack]

Thanks for the offer. I may well be wrong but stepper motors control the idling don't they and that is always fine. and she has been runnning with no problem for a couple of weeks now, which is not that unusual.

[elnevio]

I guess that there is also potential for the O2 sensor failing too. How does it run if you unplug the MAF? It should be lumpy and will run, but perhaps you can describe how similar the problem is to when running with the MAF unplugged.

[skipjack]

The main problem a the moment is the emission failure so the car is actually running fine but with high co2 emisions and showing this maf fault code. The mechanic reckons that there is also a temperature sensor in there so unplugging it would not do it any good . I think I just need to find a reasonbly priced sensor if poss

[elnevio]

Well, the MAF does measure intake temperature to allow it to adjust the fuelling accordingly. As mentioned before, I would have thought you could get hold of a MAF sensor on here.

Unplugging the MAF will definitely not pass the emissions, but it would at least give an indication of the similarity of the problem, and thus point more certainly towards the MAF. There may be a broken wire somewhere that is occasionally making contact or not, as the case may be.

The coolant temperature sender failing would cause massive overfuelling as it thinks it's cold when it isn't, so dumps more fuel in, to the point of running very badly when warm. A new sender from Camskill is really quite cheap!

I would have thought this would cause a MAF fault as the ranges end up outside of what the MAF reads, perhaps. For the price and ease of replacement, I'd consider replacing it anyway, doing a battery reset, and then seeing how it is.

[skipjack]

That is possible because it is like trying to run an engine with the choke on. I think I will try that. Thanks for your thoughts.

[elnevio]

Good luck. Do let us know how you get on!

[skipjack]

OK , I am replacing my temp coolant sensor and I have found a Maff sensor from a 98/99 facelift legnum. Is this compatible with mine which is a 97 pre facelift model? Any superior knowledge gratefully recieved.

[elnevio]

MD334005 is the part number for ALL 8G VR-4 MAFs. I'm not aware of any differences between MAFs, so I would go for it.

[skipjack]

Thanks for that , it has been very helpful

[Chris.W]

I think i got a spare maf on the leggie.
Will let you know when i get home tomorrow.