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Discussion Starter #1 (Edited)
Hi,
I drove my car to the mechanic to diagnose an engine check light and for engine idle shut off after some cold starts.
He put it on the computer and told me my mass air flow sensor needs replacing and that it was the culprit behind idling problem.
Anyway I deplugged the sensor and returned home (with the intention of replacing it another time)

Intrestingly, after an internet search about the topic, I found that some persons talk about "intake manifold gasket leak" which can simulate a bad MAF sensor

So, should I inspect manifold gasket before replacing the sensor?

PS: Workers in a spare parts shop say that MAF sensors other than BOSCH brand are unreliable. Is it true? What do you think?
 

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I've had my G for 11 years now. Am on my 3rd MAF sensor. They just don't seem to last that long - although my present one has lasted the longest. When I first fitted this one, I decided to never leave the ignition on without engine running for any length of time. There is a strip of wire which is heated, when ignition on. The resistance is measured and that determines how much air is passing through - there is also a temp sensor which corrects for density. I wondered if the wire needs air running past otherwise it gets overheated. Maybe this is why it's lasted so long - who knows !

My experience is that it won't affect idle when faulty, just driving. Mainly low engine speed, heavy throttle (not full).

The ECU will ignore it at full throttle and go onto a preset fuel flow, so any problems will immediately cease while at WOT, and come back when off the floor.

Also, if you unplug it, did symptoms persist ?
 

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Mmmm, tough one. If it was a manifold gasket leak, the (quite possibly serviceable) MAF would under-report the volume of air coming in leading to it running lean - which correspond to your symptoms. Pulling the plug would revert back to pre-mapped fuelling and therefore it would run okay again as the pre-mapped fuelling is programmed to run rich (as too lean a mixture runs hot and will damage cat etc eventually).
Unserviceable MAF would have the same symptoms !
My current MAF is a Valeo, and been in for 4 or 5 years which is the longest I've had one in. Don't think I've had a Bosch one..

If it was me, due to the notorious unreliability of MAF's fitted to G's, I'd be inclined to replace it with OEM unit (cheap ebay generics only last the 3 months to get dealers away from warranties!) as - gut feeling - finding intake manifold leak accurately could be tricky. I would think replacing it big job...?? I've not done it though, and over the years I've not heard of many having trouble with the Intake Manifold gasket - unlike MAF's! Someone else may shed more light on this though..
 

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Could you not spray something like carb cleaner around the inlet manifold when idling to see if the engine note changes to check for leaks?
 

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I've had my G for 11 years now. Am on my 3rd MAF sensor. They just don't seem to last that long - although my present one has lasted the longest. When I first fitted this one, I decided to never leave the ignition on without engine running for any length of time. There is a strip of wire which is heated, when ignition on. The resistance is measured and that determines how much air is passing through - there is also a temp sensor which corrects for density. I wondered if the wire needs air running past otherwise it gets overheated. Maybe this is why it's lasted so long - who knows !

My experience is that it won't affect idle when faulty, just driving. Mainly low engine speed, heavy throttle (not full).

The ECU will ignore it at full throttle and go onto a preset fuel flow, so any problems will immediately cease while at WOT, and come back when off the floor.

Also, if you unplug it, did symptoms persist ?
Hey Chris G, which MAF Sensor are you using? Is it OEM? I once bought a third-party one and wasn't workinng correctly. Had to fit an OEM one. Thing is this was around 6 years ago. Better be preparing for my next MAF Sensor purchase.

I do the same, I don't leave my car with the Ignition on without idling it
 

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The last one I got was from Autovaux I think, who do OEM only. It's a Valeo unit.
Agreed, I've used non-OEM many years ago and it lasted about 2 months before fault code 0170 (iirc) came back up - useless!
This latest Valeo has lasted I reckon 4 years - but yes have not left ignition on, and am doing more fast miles rather than stop start.
I'm feeling that it's on it's way out now though, little flat spots here and there, a bit of hesitancy when cold etc.

Some say you can clean them but when I've pulled old ones out the wire always looks spotless...

But Valeo I can vouch for.
 
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