idle ?

I was under the impression that under 3000 rpm the MAF was not being used by the ECU, but after 3k the "open loop" came in using the MAF to calculate (within preset peramiters) air flow and thus fuelling to suit.

My question stems from the behaviour of my car AFTER fitting the new MAF, when it was on the "way out" the fuelling was very rich on idle, fluctuating and dropping down to "night rider" mode on the AFR.

When accellerating after warm up, it would surge until above 3k, after 3k it was ok.

After todays run I have noticed that idle is spot on again, off boost driving is much more relaxed, lots of off boost torque...and alltogether a much nicer drive.

So, does the MAF have an effect on idle and low rpm ? my findings are that it does.

Any takers?

MD.

I'm fairly sure the MAF has no effect at idle - providing all is well with the thing. At idle, manifold air pressure should not fluctuate much, and should be slightly positive. This is due to the engines reduced requirement for fuel/air at idle (and the fact that the turbo is practically dormant). It is possible that if this sensor failed, it would tell the ECU manifold presure is more positive (higher) than it really is, and hence more fuel would be added to compensate (injector duration increased).

Cheers,
Leeroy

Although in closed loop, the ECU tries to run as per the fuel map. The closed loop introduces correction to the map, but it still needs it there in the first place.

So yes, since the fuel map relies on MAF sensor, the closed loop will go out the window with a bad MAF sensor.

paul

do u know what the sensor readings were like from the dodgy maf?

my car is 'surging' alot again.. had kinda stopped it.

hmm maybe i should try a new maf sensor bitty and see how it goes...
i know it 'clean' now ;)
but still might not be right.
the surging u felt... was it like a stepping of the acceleration..

... then all of a sudden it becomes smooth and continues to pull hard...?

ive heard all sorts of stories for this effect...
will be good to find out exactly the cause and solution

Thnik it might have an effect on idle as many people on here who have had MAF failure explian problems with idle and it being very rough.

Dan..:)

I recently blew the MAF on my P1.

The car wouldnt idle, it would build up to idle then drop off, then build up, then drop off, then build up etc....

So, yes, the MAF does have an effect on idle.

Cheers

P

Yup I'll second what Poc says, exactly the same thing happened on mine when my MAF shafted itself.
Idle would hunt between 1000 rpm to almost stall to finally stalling.

mine doesnt go near stalling...
but u can feel the car shuddering at idle with the hunting...

dealer noticed this too.
cant solve it .. yet

SCOSaltire,

Mate, I've got exactly the same problem as you by the sounds of things. If you get it sorted please let me know and vise versa of course

Cheers

Guy

PS How much does it pis5 you off

SCOSaltire, yes thats exactly what its like...when I described it to by son (Mole of course), I said it was "vooph, vooph, vooph" then into hyper.

Before the MAF change the idle was really poor (worse when cold), sometimes, mainly in traffic, the revs would drop to 400rpm, surge up to 1000rpm and settle around 890rpm...usual idle has always been 900rpm, no deviation.

I also had promising results from cleaning, but Sunday was GAME OVER !

Thanks to the other guys for the replies, I can understand the theory of the pos pressure bit, and I think that what has happened since changing the MAF has proved that it must have an effect on low speed and idle.

I just hope and pray that my changing the induction and cold air pipe has the desired effect and lets my MAF live a long and happy life :)

Cheers all, MD.

PS, perhaps a plug in box to trick the ECU into thinking it has XX air flow would be a good (lucrative) project for some tekky person, or does it have to be 'real' info for the ECU to work?

The MAF is used all over the map along with RPM.

You could convert to speed-density using the MAP sensor and using a microcontroller to feed the JECS with a simulated signal, but to do it accurately you would need to know the intake temperature.

To be perfectly honest with you John, I have no intention of an alternative to the MAF as long as it continues to perform as it should.

I suppose that if I had not *uck** with it, it would probably still be perfectly happy sitting in its tunnel of air!

If I had the money I would go for a Link ECU and be done with it, at the moment I cannot do that, and I feel (at present) that my UK car at around 290bhp is probably as far as I want to go.

I am still unsure as to whether the problem came from oil mist from the filter, water ingress (along with the barrow load of grit) or vibration due to the MAF housing being strapped down with cable ties. (To clear FMIC pipe).

Whatever the reason, I am very glad that I got mine 5 times cheaper than the price I first saw on this bbs.

Cheers all, MD.