Where is the MAF and how to check it?

[Aus 0]

Got a prob - when coasting to a stop it often (but not always) dies and when starting from cold, it always starts but idle hunts until warm, and if driven before warm, engine often dies. This problem is variable, was awful yesterday and has been perfect today! I gather this is not an uncommon problem, but so far have:

 

- replaced blue temp sensor

- replaced ecu relay (this seemed to help, but after a few drives, returned to poor form)

- garage replaced coil pack and leads at huge cost!

- replaced battery (this seemed to help, but after a few drives, returned to poor form)

- cleaned ISV (this seemed to help, but after a few drives, returned to poor form)

 

Gather checking the MAF would be worthwhile - where is it? And how to check it's OK?

 

Getting a vag-com done locally seem v expensive (VW say min 3hrs at £70 per hour!).

 

Many thanks (and thanks for all the advice so far)

[h100vw 0]

For that money you can buy your own VAG-COM.

 

It doesn't take 10 mins to scan for faults. Most of that is waiting for the laptop to boot.

 

Just for the record, it is a VR right.

 

Gavin

[Aus 0]

and after searching on here for a bit, I saw a thought from Kevhaywire:

 

"Someone mentioned to me once that odd stalling like this could be a brake servo on it's way out or leaking. They take too much air as you're pulling up to a junction and the ISV struggles. Don't know how feasible that is, but it sounded good anyway, LOL! "

 

I reckon my stalling happens more often under braking than not, and I occasionally get my abs light coming on (always goes away after stopping and re-starting) - would that tie in with Kev's thought?

[h100vw 0]

The ABS light is more likely to be a sensor. Ign off and on just reboots that as well. My old GTI G60 did it.

Gavin

[Aus 0]

yep - it's a '94 VR6

[Dutch24V 0]

Not being funny but check all the pulleys on your aux. belt by releasing the tension and turning each by hand.

 

I had the exact same symptoms and it was 80% fixed by a new MAF, and the other 20% came when I replaced the water pump too. Until the water pump was replaced she would still hunt on startup and sometimes stall when cruising to a stop with clutch in.

 

If my water pump wasn't shagged the MAF would have fixed it totally, but because the resistance on the aux. belt was so high it created idle and stalling problems at low rpm (no torque to combat the resistance I think)

 

Dutch

[vr6corrado 0]

By the way the MAF is on the side of the ducting after the airbox.

[Aus 0]

thanks - looks all clean - any easy way to test it's working OK?

[Kevin Bacon 5]

Not really..... a basic test you can do is hook a multimeter into the red wire of the MAF loom and earth and check it's giving 2V at idle and check the voltage goes up as you rev it. I had a MAF fry on me once and that gave 12V down the red wire, LOL!, and the ECU can deal with 5 max! That caused all manner of running problems at the top end. Try a long cotton swab with some alcohol and very very gently wipe the platinum wire.

 

This stalling at junctions is very common.

 

A few things you can try:-

 

1) Look behind the throttle and you'll see a little white plastic piston which catches the throttle and lowers it gently to rest. It's adjustable (13mm spanner underneath) so you can wind it up to catch the throttle earlier.

 

2) Clean out the ISV thoroughly with alcholol and clean up the scoring marks off the internal valve with cotton buds, then lube it with silicon maintenance spray. Rapidly flick the ISV in your hand left to right and make sure you can hear and feel the valve flapping about. If it doesn't it's seized.

A further test is to connect some jump leads from the ISV connectors to the battery and pulse the negative or + lead on and off about 30 times. Each time you pulse the power the valve should open, if it binds during the test, replace it.

The trouble is, the ISV sits right above the hot manifold and expands, which can cause intermittant valve binding.

 

3) Check for air leaks. With the engine up to temperature and idling, spray some carb cleaner round the intake hoses and joins (and the brake servo). If the engine revs rise where you spray (carb cleaner is very flammable), that's where your leak is.

 

4) Check for broken wires and corroded connections and make sure the MAF plug has the clear rubber seal inside it. Sometimes they drop out allowing water to contaminate the connections.

 

5) Make sure all 6 plug leads are firmly located. Sometimes they don't click onto the plugs solidly and arc across the improper connection.

 

6) Check plugs 1 and 6 for oil fouling.

 

7) Clean up the throttle butterfly and remove oil residue from the intake hose.

 

8) If you've got VAG-COM, check the throttle position sensor or replace it if it's really old, they're £40 from the dealer and have been improved. An ECU reset will be needed after fitment, so pull the ECU plug and reconnect after a couple of mins. Also check for Lambda probe and cam sensor errors. Or you can check the lambda with a voltmeter - Meter + to white wire on the Lambda loom (on rear engine mount) and Meter - to earth (chassis). When up to temp (after 2 mins from cold), the voltage should rapidly fluctuate between 0.1 and 0.7V. If it's stuck on 0.45V, it's dead.

 

9) If all that fails, replace the MAF. You can get them exchange direct from Bosch for £150, which is a lot easier on the wallet than VW's cost of £337!

 

I can't promise that will solve your problem. I never cured it on mine in 3 years of trying. It is now though, but only because I've changed the complete management system.....but at worst it used to stall 4 or 5 times a week and at best 1 or twice a fortnight.

 

Good luck!

[Aus 0]

thanks kevhaywire - given me a few ideas for the weekend!

[Kevin Bacon 5]

Give it a whirl, should keep you busy for a couple of hours 8)

[Aus 0]

"couple of hours" and some! But reassuring that some of you much more experienced chaps have had similar challenges!

[Kevin Bacon 5]

Getting a VR to run factory fresh all the time is an ongoing challenge in itself!

[vr6corrado 0]

Thanks Kev, answers my questions on a similar thread I revived.

[Aus 0]

For what it's worth - took the MAF off, cleaned the connection box and WD40'd it (altho it looked fine) and adjusted the white plastic piston, and it was perfect on a short run today. Albeit, I'm slowly learning that this problem seems to come and go of its own accord!

[vr6corrado 0]

Same here, mine runs much better now after a clean up and running those checks :)

[Aus 0]

Mine's still running spot on (not wanting to speak too soon though!)

 

Thanks for all the help, esp kevhaywire's comprehensive list! Cheers