Why does disconnecting and reconnecting my MAF make it run great for a while?

[aclwalker 3]

Got a strange one with the VR6. I know there's loads of MAF/hunting/poor idle threads but I've never seen this problem.

 

My car hunts when I first start it and also does the famous nearly/actually cutting out at junctions etc.

 

However, I've noticed that if I simply unplug my MAF then reconnect it, the car runs beautifully, immediately, without me having to do anything else. The power is great, the idle smooth and it's a joy to drive.

 

After a while (a week maybe) the problems start over again, and I repeat the cycle. I thought my MAF was dodgy, so I sourced a second hand one, and it still does it (it generally runs a bit better on the new MAF however). This 'reset' procedure works whether or not the engine is running when I disconnect/reconnect. If I do it quickly enough when the engine is running then it will splutter, but not conk out. It'll rev quite high for a short while and slowly lower. It's almost as if this process resets something in the ECU.

 

It's a bit of an IT Crowd solution, I know! Any ideas what's going on?

 

Any ideas for a more permament solution? I've ruled out the coil pack (got two coilpacks), the HT leads, the spark plugs and now, I think, the MAF itself. I'm wondering about a loose connection in the plug, or an ECU issue?

 

Thanks for any help guys.

[swiftkid 1]

Have you had it on VAGCOM? Have you tried simply spraying WD40 into the MAF plug? It could just be that its got dirt on the connection. Another thing to question is, is the second hand MAF you have got a working one? I'm afraid they are very temperamental things and can easily get damaged in the post. Is it an early or late style MAF? ie is it a 4 wire black plastic casing or a silver and black one?

[dr_mat 0]

I assume this is a OBD1 hot wire MAF not the later film type. I think the older ones have a four-pin connector.

If you unplug and replug the MAF while the ignition is ON, the ECU will switch to only using the throttle position sensor to determine fuelling, and it'll probably run a shade rich. It may also run a MAF cleaning cycle (heat the wire up to burn crap off) before bringing it back into use.

If you unplug it while the ignition is OFF, it will make NO difference whatsoever so you'd have to assume any effect is either imaginary or related to connectivity or debris build up inside the MAF.

[floppyman 0]

Do you have the original air filter? The maf plug might be the problem, with the engine running try to move the plug and see if the engine changes tone... If not then I would star with a ecu reset, the whole reset following RW1 wiki

[aclwalker 3]

Have you had it on VAGCOM? Have you tried simply spraying WD40 into the MAF plug? It could just be that its got dirt on the connection. Another thing to question is, is the second hand MAF you have got a working one? I'm afraid they are very temperamental things and can easily get damaged in the post. Is it an early or late style MAF? ie is it a 4 wire black plastic casing or a silver and black one?

 

Hi, I've had it on VAG-COM before but no codes. I've got VAG-COM, but my computer is broken now so I can't re-scan it right now. New computers don't have serial ports any more!

 

I've cleaned up the MAF plug before and I actually replaced one of the pins ages ago because it was splayed open and caused even worse problems then. This repair made the problem much better but it seemed to come back.

 

The second-hand MAF I'm pretty sure is working. Even with the hunting it's running better than the old MAF. It's the 6 pin MAF (well 6 pins but only 5 connected).

 

---------- Post added at 12:51 AM ---------- Previous post was at 12:48 AM ----------

 

I assume this is a OBD1 hot wire MAF not the later film type. I think the older ones have a four-pin connector.

If you unplug and replug the MAF while the ignition is ON, the ECU will switch to only using the throttle position sensor to determine fuelling, and it'll probably run a shade rich. It may also run a MAF cleaning cycle (heat the wire up to burn crap off) before bringing it back into use.

If you unplug it while the ignition is OFF, it will make NO difference whatsoever so you'd have to assume any effect is either imaginary or related to connectivity or debris build up inside the MAF.

 

Hi, it's the older hot-wire one, but it's 6 pin (only 5 pins used though). If I unplug it while it's running the engine stops. I can unplug and it and replug it very quickly and it'll splutter but catch again, rev quite high and slowly come down and the hunting and poor running will be gone for a short time.

 

I'm really beginning to think I've got a wiring issue. I had a duff pin before which I replaced and it made the problem better, but maybe some of the other wires are failing. I always think the MAF connector seems very close to the bonnet. I sometimes wonder if the engine pushes the connecter against the underneath of the bonnet, stressing the pins, especially if the engine mounts are worn.

 

---------- Post added at 12:52 AM ---------- Previous post was at 12:51 AM ----------

 

Do you have the original air filter? The maf plug might be the problem, with the engine running try to move the plug and see if the engine changes tone... If not then I would star with a ecu reset, the whole reset following RW1 wiki

 

Yes, I think I'll try moving the plug and/or wire while it's running and see if I can detect a break. Unfrotunately I can't do a full ECU reset just now because my VAG-COM computer is broken now. I've done the battery disconnect ECU reset, but I guess it's not as good doing a proper one.

 

Sorry, not sure what you mean by original air filter. It's a 222000+ mile Corrado, so it's had it's fair share of filters! :) If you mean air box, then I think it's all original. I haven't replaced anything, but I know my oil filter housing is from a newer VR6 engine (large bore element rather than smaller one), so things have been changed on the car before I got it, although it's standard as far as I can see. No induction ktis or anything.

Edited December 20, 2011 by aclwalker

[easypops 8]

Hi mate, I have vagcom(the free lightweight one) running ok on my laptop, happy to pop over with it if you think it would help, won't be able to do the basic settings as that's locked on this version, seems to do fault codes ok though........ and I still owe you one from when you scannd mine a while back :)

[aclwalker 3]

Hi easypops. Thanks for the offer, but I think I've finally found the problem.

 

I agitated the wiring for the MAF quite a bit in frustration a few weeks back and the car has been running great since, so I think I must have a broken wire, right near the plug. I had a broken wire in the past, which I repaired, but maybe the repair has failed.

 

Lots of electrical gremlins in these cars. My courtesy light won't go off as of today!