S7EV3N

Got a MY99 Turbo wagon and there seems to be a lot of talk on here bout maf sensors. Trouble is...i dont even know what it is. Can you help ?
What is it ? Where is it ? Wht does it do ? How do i know if its broke ?

Some ppl seem to recommend changing it as the first mod on my new motor. Is this neccessary ? If yes...how do i do it ?

micared

Maf sensor measures the flow of air between airbox and engine....its located to the right of the airbox, as you look from the front, held in from behind by 2 small torx bolts....10 minutes to replace, if that. To check it, disconnect your battery ( make sure the radio code is to hand ) for, I think, one hour ( prepared to be corrected here ), certainly no more than that, reconnect and drive. If the car misbehaves, ie, won't idle, severe hunting etc, assume the worst and get your £77 ready! Some people, myself included, treat them as a service item, and change them regardless....if I bought a scoob at the mileage yours is at, and there was nothing in the paperwork to show if it had been renewed, I'd change it. If you don't, and the maf causes the car to run weak, the resultant det will, in all likelyhood, either hole a piston, or knock out a big end...big money either way. If you've any doubt, for £77, it doesn't make sense to take the chance.

The_Judge

First of all, a picture. The connection to it is a small grey beasty, just beneath the throttle cable and where the 2 coolant hoses do a right hand turn toward the coolant header tank. About 2 inches to the left of where it says 2. Driver manifold, and 2 inches below the alarm siren.



Some points I made on a recent thread, regarding MAF checks/failing symptoms...

1. With the engine warm and idling, pop the bonnet and disconnect the MAF sensor. You don't need to unscrew it, just unplug the connector. If the engine stalls, the MAF is probably OK. If there's no (or little) difference in idle, the MAF is more than likely failing.

2. Reset the ECU. There's a simpler and quicker method than disconnecting the battery. Click here for info on that. If the car drives more or less the same after the reset, the MAF is probably OK. If the car drives worse after the reset, the MAF is more than likely failing.

3. Whilst in neutral, blip the throttle so the revs go to around 3000rpm. Then watch them as they fall. As they approach 1200rpm, they should slow down and settle gently at ~800rpm. If they fall at a constant speed and then nearly stall, or hunt rather than settle at 800rpm, it's another possible indication of a failing MAF.

4. An AFR of less than 0.75/0.8v at WOT, using standard lambda (not wideband) and Autometer AFR gauge or equivalent.

5. Faster than usual performance - the leaner AFR, and ignition timing too advanced as a result, will make the car fly... until it starts to det (see below).

6. Excessive Knocklink activity - the lean AFR, and the over-advanced ignition timing, will eventually lead to det. If you haven't got a Knocklink or det cans to be certain, you may be able to hear it, or you may feel a "bogged down" feeling in acceleration.

As Micared says, it's not worth the risk of fannying around with MAF sensors. They should be treated as a consumable like an air filter, and changed regularly. And as they're only ~£77 from your local dealer, it's a no-brainer. The part number is 22794AA010 Meter CP-Air Flow.

freshtripe

I've got the fluctuating idle problem on my 97 WRX Wagon - is the MAF part number the same for this model?

The_Judge

Unfortunately no... and I couldn't tell you what it is I'm afraid! How many of the above tests/symptoms are applicable to your situation?

freshtripe

This morning I tried unplugging the MAF sensor and the car stalled straight away, just as it should have done...

Should I try cleaning the ICV and resetting the ECU (as recommended elsewhere on this board) before doing anything else?

The car was serviced yesterday (full monty inc. plugs, belts, etc.), but the garage did not reset the ECU - the car had been run on 95RON petrol for a couple of weeks prior to my ownership, now its got a tankful of 98RON Optimax + booster - would this make any difference?

Lots of Qs - sorry, but thanks in advance for any help.

The_Judge

If the ICSV is playing up, the revs are normally static (no hunting), but higher than usual. 1200rpm isn't unheard of.

How's the car driving? Normal? Slower than usual? Faster than usual? Hesitation/bogged down at certain revs/gears?

An ECU reset is probably next on the list. When you go for your drive during the reset procedure, make a note of how long it takes for the CEL all clear to flash (assuming it doesn't find anything wrong!). If it takes a few seconds, it's a good indication that most important bits under the bonnet are OK. However, it could take up to 10 minutes (as it has done on mine in the past when the lambda sensor was fcuked). This indicates there's something the ECU's not happy about, even though it might not give you a CEL error code. Lambda sensor is a common one, and might even be a contributing factor to what's wrong with yours.

The fuel shouldn't make any difference to the idle. However, 95RON fuel probably wasn't a good idea! Do you know if the previous owner kept off boost whilst that was in?

What were the plugs like that came out? They can give quite a good indication of the condition of your pistons. If any of them look melted/cracked/blown to pieces, time to give David API a call to book an appointment...

freshtripe

Thanks for the advice - I will try an ECU reset tonight.

The car felt a bit less potent than usual last night - unfortunately I didn't see the state of the plugs when they came out, but the garage remarked that nothing seemed untoward, fluids were pretty clean, etc.

As for the 95RON fuel - I doubt he did back off...

The_Judge

Best of luck.

minor_threat

Judge,

you should turn your post into a MAF FAQ - highly informative! The previous owner of my car (MY00) had fitted a K&N induction kit so I'm keeping a close eye on the MAF sensor. After reading your replies I'm confident I know what symptoms to look for now and diagnose signs of failure. Thanks.

The_Judge

Cheers! Shame Ozzy's picture seems to have vanished... *Must get round to doing some of my own*

The_Judge

The FAQ section could do with an update... Oi, Webmaster!

Turbo_Steve

Not arguing with anyone here, but mines done over 150,000 miles, 80,000 of them with an HKS induction kit on, and still works just fine (touch wood).

APIDavid

iTrader: (4)

I bet you're the sort of guy thats walks under ladders. I wouldn't dream of saying anything like your statement. Now, where's my lucky rabbits foot just in case you've tainted me remotely........

David API Engines / API Impreza

freshtripe

OK - I have reset the ECU, but the problem is stil there, albeit to a lesser extent (I used the battery method(!) so no codes I'm afraid).

When I blip the throttle the revs come straight down to 1000rpm, then slowly drop to 750-800rpm over about 10-20 secs. They would then hold pretty steady with very occasional hunting (one flutter a minute, say).

I'd like to clean the ICV and the TPS, but I don't know where to locate them on my car. My engine bay does NOT looks like the picture on this forum:

http://members.lycos.co.uk/subaru/sc.../coloured2.jpg

It looks more like project WRX engine bay in the "Japanese Perfomance" mag - any one got an issue and a marker pen handy?

Thanks again
Freshtripe

a18 ryk

sounds like maf to me if its gone its killin u engine it killed mine will cost u over 2 k

The_Judge

I don't think it's your MAF.

Test 1 - Unplugged MAF - engine stalled (as it should).

Test 2 - Reset ECU - idles OK (ish) and drives no worse than before reset.

Test 3 - Blipped throttle - revs dropped to 1000rpm and slowly settled at 800rpm.

Test 4 - Don't know.

Test 5 - Performance is slightly less than normal, so it isn't running lean.

Test 6 - Don't know.

I think you should reset the ECU again, but using the plugs instead of disconnecting the battery...

You could also try disconnecting the lambda sensor to see if that makes any difference to idle/part thottle.

Turbo_Steve

I concur with the judge: It sounds far more likely to be your lambda sensor than your MAF.
Does it idle okay when cold, and then develop the problem as it heats up? This is always a good indication that as the ECU comes out of cold start and starts using the lambda sensor it is getting innappropriate readings and battling to keep a smooth idle.


And yeah, I like standing under ladders and waving upwards

My car has actually had all sorts of things go wrong, but none of them are the things you read about on Scoobynet. I always have to be different...........

freshtripe

Also noticed an engine speed dependent tapping noise this morning (only really audible between 1000-3000rpm, drowned by engine noise above this).

Just taken the car back to the garage where the service was done (David Hendry in Malmesbury). They reckon that one of the cylinder heads on the car is newer than the other and that a badly seated valve in the newer head is causing the noise/idling problem. Looking an 6 hours labour to strip it down and inspect.

Are they just after my money, or does this sounds right?

Anyone know where I can take it for a second opinion in the Costwolds Area (Powerstation in Cheltenham perhaps?)

Thansk in advance.

Turbo_Steve

freshtripe

OK - update.

Took the car back to David Hendry and after much sheepish-ness they admitted that they had set the timing incorrectly when changing the cam belt. Tapping noise and idling problems have now dissapeared.

However, now the car will not boost above 0.5bar - they tried a known good MAF, MAP sensor and boost solenoid swap, but this made no difference. They reckon ECU problem, but given the accuracy of their last diagnosis...mmm...any ideas.

I would like to try an ECU reset, but I don't understand these instructions:

http://www.saxonfields.freeserve.co....e.htm#_Sensors

The links to the "connect read memory connectors" image does not work.

Loads of Qs again, apologies and thanks in equal measure.

Freshtripe

Turbo_Steve

Sounds like a possible sticky boost solenoid, or faulty piping.
Does the car sound more "Wooshy"? It's possible your intercooler pipe has split?

The_Judge

ECU reset, piece of cake mate...

- Preferably start off with a warm engine.

- Get yourself in the drivers' footwell.

- Have a look up by the steering column for 2 small black connectors, and 2 larger green connectors. They'll both be on tiny wires.

- Connect black to black (read memory connectors) and green to green (diagnostic connectors).

- Turn ignition on (not engine), and ensure solenoids, relays, and rad fans can be heard cycling from engine bay.

- Press accelerator pedal to floor, hold for 2 seconds.

- Release pedal to half throttle, hold for 2 seconds.

- Release pedal completely, start engine.

- Go for drive. Use gentle acceleration (not WOT).

- Wait for CEL to start flashing.

- If everything's OK under bonnet, it may well flash the all clear within 5 seconds of driving.

- If something's failing (as opposed to failed), it could take up to 10 minutes to flash the all clear.

- If there's a fault, it will flash the corresponding error code.

- Pull over, kill engine, disconnect both sets of connectors.

- Job done.

freshtripe

Thanks Judge - I'll try it tonight and let you know how I get on...

dij

BTTT

I would like to know the outcome of this.
I have a similar problem with the boost on my car.

Have you tried cleaning the boost cont solenoid?

You could try to drive with the pipe to the solenoid (from turbo)disconnected to see if it actually boosts higher,although it may not be a good idea to do this for too long.

freshtripe

Nothing's ever simple is it...?

Had a look in the footwell today (in the brief moments between rain) and found that I have 1 yellow connector, 2 green connectors and 3 (yes, three!) black connectors.

The black connectors consist of 1 female and 2 male - any guidance on what colour wires should be going into the male black connector so that I can distinguish between them?

Looking at the mass of electrical tape under my dash I am becoming increasingly suspicious that the previous (Japanese) owner had fitted some sort of boost controller (the car has a boost gauge fitted)...

Need some expert advice, Judge!

freshtripe

Just read your post Turbo Steve - the car does indeed sound "whooshy", but more than normal? I don't know - the car has sounded the same ever since I've had it (3 weeks).

The more I think about it the more I'm sure that the car has never boosted above 0.5bar in my ownership - I didn't spot it straight away 'cos I was taking it easy prior to the cambelt change...

Bob Rawle

Easy way top reset the ecu .... disconnest the battery for 30 mins then reconect.

Once reconnected drive the car gently, the ecu will be in "safe map mode" to start with, find some clear road, start at 2500 rpm in 4th or 5th, EASE, and I mean that, ease the boost up to about 0.9 bar gently ensuring that its there by about 3800 rpm, hold till you get to 5800 rpm, that should click up the advance multiplier if alls well, now it will fine learn and you can drive normally.

Thats ALL you need to do to start the re-learning process.

Boost should be 0.95 as normal dropping to 0.67 at high revs.

Check the boost pipework, make sure that the turbo outlet pipe is not directly connected to the actuator and that it does have the correct size restrictor in place.

cheers

bob

freshtripe

Thanks Bob - I'll disconect the battery now and let you know how it goes.

In the meantime here is an under bonnet pic - is everything plumbed in correctly?

http://photos.fotango.com/p/eba00450735f00000001.jpg

Thanks in advance
Freshtripe

freshtripe

OK - I reset the ECU, but made no difference - time to try some plumbing....