Engine 850: B5234T/2.3/20v/T5: MAFF Senser

[stevepcar]

Hello I have been trying to get my T5 back on the road after a 7 year lay up. I had the EML come on and when I tested the codes it pointed towards the TPS, so I took it off cleaned it and the throttle . This seemed to do the trick & it went thru the MOT after changing a bulb & a ARB link. I've also had the auto gearbox light come on. So I flushed the old oil out with new fluid & the light went out. So feeling quite pleased with myself I took it for a test run, however after about 2-miles the EML came on again. So I took it straight home & read the codes it came up with 2:3:1. I had seen a U tube video saying that to check the MAFF senser you just unplugged it & if engine kept running then it was faulty. I tried that and it kept running, so I cleaned it with MAFF cleaner, but that didn't make any difference. So I bought a new MAFF senser.... engine still keeps running if I unplug the senser. Is that not a foolproof way of testing it, or could there be some other problem causing the engine to keep running with it unplugged? I have tried tracing a leaky vacuum line with carb cleaner, but I didn't notice any difference in the engine note.
Hoping that someone can help as I am at the end of my tether.

[Luxobarge]

Whether the engine keeps running or not is not a way to diagnose MAF faults. If the MAF is faulty, the ECU will adopt default values for it, these will be inaccurate but enough to keep the engine running more or less OK and get you home. Therefore if you unplug it the ECU will substitute default values and the engine should indeed keep running. If the MAF is very bad, then sometimes unplugging it can actually make the engine run better - this is a strong indicator of a MAF fault but not simply whether it runs or not.

What MAF did you use to replace it? Reason I ask is that these engines are very picky about MAF quality, and generally cheapo aftermarket replacements are not good enough, and quite often worse than the faulty one. To be sure you need to replace it with a genuine Bosch unit of exactly the same part number. I know this is probably going to be a lot more expensive, but a cheap one is false economy as it just won't work correctly in all probability.

You also mention a "leaky vacuum line" - this is a strong possibility, vac leaks can often produce symptoms of a faulty MAF, and you should be 100% certain that you don't have any vacuum or induction leaks of any kind before condemning the MAF.

[stevepcar]

Thanks for that. I replaced it with a part from Euro Carparts, not a Bosch part though. Unplugging the old MAFF or the new Maff makes no difference anyway, so I suspect there is something else wrong. I will keep checking the vacuum lines. When it failed the MOT 7-years ago I got the same code. It's been off the road ever since with occasional start ups. All I did to get it through after the long lay up, was to put Cataclean in the tank & take it for a fast test drive. The EML has been off ever since. I have only done about 15-miles in it since the MOT, as I have been sorting the auto gbox light.