Dying MAF? With some durametric logs

[nizzki]

My 2002 turbo tiptronic occasionally almost stalls when coming to a stop while it's warming up. It dips down to 500rpm or so, maybe even less, but it then bounces back up and keeps running.

It stalled on me completely a couple times, but that stopped once i replaced the air filter.

I've tried cleaning the MAF, and I *think* that it helps, but i can't convince myself that the MAF is the problem because it's rather intermittent.

I tried capturing some durametric logs, here's the relevant part:

RPM THR KPH MAF V AFR

801 4.3 16 1.5 0.92 0.89

778 4.3 15 1.46 0.93 0.9

732 4.3 14 1.5 0.94 0.92

711 5.7 13 1.64 0.95 0.93

695 5.8 12 1.59 0.96 0.94

658 5.9 11 1.62 0.97 0.95

627 7.3 10 1.73 0.98 0.97

606 10.1 9 1.96 0.99 0.99

602 11.3 8 1.99 1 1.02

604 12.4 7 1.99 1.06 1.07

532 12.1 6 1.88 1.15 1.13

578 17.6 5 1.97 1.24 1.18

558 16.1 4 1.88 1.29 1.22

659 11.6 3 1.75 1.31 1.24

778 5.2 3 1.44 1.25 1.19

855 5.2 2 1.55 1.17 1.15

The weird thing is that the throttle actual value goes up as the car slows down, but i don't know if that's in response to the MAF reading, or if the MAF reading changes because of the throttle.

Either way, other symptoms would kinda go along with a bad MAF, such as occasional rough idle, when i let off the accelerator and than step back on it it sort of burps(?)

Anyway, does anyone know if this sounds like a dying MAF or not?

I don't have any CEL's, but I know it's possible for the MAF to be on the way out without hitting those. I'd try driving without the MAF plugged in, but the symptoms aren't constant, so it'd be hard to prove anything.

Thanks!

Edited July 14, 2012 by nizzki

[Dus10R]

Remve the throttle body and clean the hell out of it...probably gunked up. Then when you put it back on, turn the ignition on but dont start the car and go back by the engine bay and wait for about a minute untill you hear a whine and few clicks and then when the sound stops turn the car off. Then start the car and let it idle for around 10 minutes or so. This resets the throttle body and idle control...

[nizzki]

Remve the throttle body and clean the hell out of it...probably gunked up. Then when you put it back on, turn the ignition on but dont start the car and go back by the engine bay and wait for about a minute untill you hear a whine and few clicks and then when the sound stops turn the car off. Then start the car and let it idle for around 10 minutes or so. This resets the throttle body and idle control...

That helped for a while, but it seems like it's starting back up over the past week or so. I had the y-pipe off again 2 weeks ago or so and it was still spotless clean, so i doubt it got all nasty already.

[Dus10R]

Are you running a stock air filter or do you have a oiled unit like a K&N or other brand?

[Dus10R]

2nd thought...when you cleaned the TB did you remove it from the car or just clean it while connected?

The best way is to remove it entirely, its easy...one connector and 4 bolts.

You can manually push the throttle plate open with your finger and you should feel some tension and then it should close itself, but not all the way, it will leave a very small opening, but you should be able to push it closed with your finger and then when you let off it should open up just a bit. Its usually not a bad idea to also remove the throttle plate from the cross bar and then polish the inside of the cylinder, making sure its smooth. There are two Torx bolts holding it in place and once you remove them it will only slide out in one direction due to there being two small bumps on the plate that wont fit through the bar. Before taking it out just note how its positioned in there and put it back the same way. I even use some very good gun oil called Zero Friction which has nano fluoro-polymers in it and I put a drop or two at the friction points where the cross bar goes into the walls of the throttle body and then work the plate open and closed a few times. This last time I did it, on a car I just bought, I removed the throttle plate and sprayed just around the outside diameter with a Kimball Midwest product called Graf-Coat which is dry graphite lubricant that goes on just like black spray paint. The aluminum throttle plates aren't the smoothest around the outside edge, It doesn't appear to me that Bosch polishes them, so when the TB's start to gunk up, the gunk sticks to the outside of those plates fairly easily; the graphite coating should help with that problem too.

But what you describe is very very common symptons for a fouled up TB, and the fact that it got better after you did it the first time tells you something too.

But if you are running an after market air filter that is oiled, it could be over oiled and dirtying up the MAF and the TB. Buy some electronic contact cleaner from Radio Shack and spray the hell out of the MAF. MAF's usually don't just go bad, there's usually a 3rd party acting on them to dirty them up which can make them fail. However, there are rare cases when the transducer lead can break inside the housing and then its for sure a gonner. I think you can see if its good or bad via Durametric... If memory seves me the MAF should read out voltage. In Durametric go into the DME and go to "see actual values" click on the MAF. With key on but not running the voltage should read .9 to 1.1 with engine running at idle it should be 1.2 to 1.5 and it should increase linearly when you apply more gas. You can also check this manually but its a little more difficult and you need a voltage meter. You keep the MAF plugged in and you need to put your voltage meter probes on pin 2 and 4 (should be labeled) on the MAF plug which you get to by pulling the rubber cover back away from the plug...

Just my personal opinion here... But if you are running an aftermarket air filter like a K & N, the real life gains (not what they claim) aren't advantageous enough in my opinion to offset the superior flitering ability of the OEM paper air filters. I ran an OEM paper filter on my K24/18G car with less problems and no noticeable difference in power. Id rather have superior filtering than a few additional HP's.

Hope you get the problem resolved, no fun having quirks.

[nizzki]

For posterity and in case anyone runs into similar problems, it appears that the MAF *may* have been dying very slowly.

After having the car stall a couple times and almost stall quite frequently this summer, i decided to try cleaning it again. I was a little too vigorous with cleaning it this time and after putting it back in I got ABS/PSM lights, followed later by P0104.

I got a new Bosch MAF on Amazon, popped it in, and the car appears to be doing better. I don't want to jinx it, but in the past week i haven't had any more stalls or near-stalls.

When the car is cold and i put it in gear, it will dip down to 600-650, but it doesn't sound/feel like it's about to die on me.

We'll see in another week or two if that really was a problem, but it's looking promising so far.