Fact or myth. MAF or vacuum leak?

[Motas88]

Have the awkward problem of P1171, rich cold idle, rough idle, hesitation and no power above 3000 revs.

Been working my way through the lines, intake and then will be the more expensive stuff.

Discounted the MAF due to some possibly incorrect information from a friend that knew a ‘Technician’ and doing the unplug while running test that’s been about.

After hours scrolling decided to revisit the MAF. Took for a run while MAF was disconnected and all is well. Power is back, full Rev range and no lumpy idle or petrol smell when cold.

Before I give up on the vacuum leak hunt and just replace the unit. Will running it with MAF disconnected mask symptoms of a vacuum leak? Cannot find a definitive answer or question addressing this although has been mentioned in posts here and there.

[Cookeh]

No, a disconnected MAF will not mask a vacuum leak. Easy enough to test for yourself. Disconnect the MAF and then pull a vac line off.

[Motas88]

Originally Posted by Cookeh

No, a disconnected MAF will not mask a vacuum leak. Easy enough to test for yourself. Disconnect the MAF and then pull a vac line off.

Ah good. Just second guessing as I know air flow values return to pre-sets when no signal from MAF. But guessing if there was a vacuum leak the O2 sensors would still through a code? Did get a running cooling fan and ETS light when I turned off after run. Had to disconnect the battery to stop the fan. (Remained off when battery reconnected). Could this also be related?

[Luxobarge]

If you do end up replacing the MAF, beware cheap aftermarket units, these cars can be picky about MAF quality, and cheap ones usually end up being false economy. Best to try to fit the correct part number Bosch unit, then you'll know it's good.

[Alpine]

I might have the same problem, if I disconnect my MAF it runs okay.

But from what you say above, could this still be a vacuum leak?

I've been looking for a new Bosch MAF (part number 0 280 217 107) but everywhere (including eBay) says out of stock, I guess because its an old part. Does anyone know where I can source one from, otherwise I may have to get a cheap one from somewhere like here http://www.autosensors.co.uk/en/306-...280217107.html

[DSK]

FWIW, for vacuum leaks I'd just use a smoke machine as that will easily find it as you can't always do it well if you can't see or replicate the issue by hand and sight.