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!

 

Simple test...remove the MAF. I know I am probably alone in this, but the MAF either works or it doesn't. I have never found any advantage to cleaning the thin film MAF. I have blown several (using the EVOMs intake...many years ago). Seems to me you have another issue...is your car flashed? When was the last time you cleaned the TB?

 

Because this doesn't occur 100% of the time, not even 50%, unplugging the MAF won't answer the question, and i don't know if it's a great idea to drive with the MAF unplugged for days on end.
Btw, no mods, and i haven't cleaned the TB, but i've owned the car for onlu 10k miles or so. There's a fairly decent chance that it hasn't been cleaned in a while though.

 

Using your same logic, then how could you possibly suspect the MAF?

 

Because the symptoms match with what people experienced when their maf was failing. I'm not saying that it isn't the throttle body, I'll give cleaning it a shot.
my main point is that it can sometimes be a couple days between instances of this, and I don't want to drive around without the maf that long.

 

I had this exact same symptom. Twice. Different things each time:

First time: Fuel pump was failing. There is a short U-shaped hose that is black on the original pumps that splits. You can open up the fuel tank and look inside.

Second time: Air leak between the maf and turbo.

The first one I found from looking at the injector duty cycles, second I found by pressure testing the intake.

Good luck.

Jon

 

I took the y-pipe off and cleaned out the throttle body. it was pretty gunked up, I doubt it's ever been cleaned. I haven't had a chance to test it out yet, we'll see if it helps tomorrow.

 

Thanks for suggesting the TB cleaning, i did that 1-2 weeks ago and the car seems to be doing much better now.
The RPMs haven't dropped on my again since, so it *seems* to be resolved.

 

So it helped for a while, maybe 3 weeks, but over the last week the RPM's have started dropping occasionally when putting it in reverse or stopping up a hill.
I had the y-pipe off 2 weeks ago and it was still clean, so i don't think that's the problem again.

odd.

 

Vacuum leak? A smoke test would definitely help find the source of the leak.

 

i just replaced my MAF for the third time in a year, and this time got rid of the bmc filter i've been running ( which i am finally prepared to say, was contributing to premature MAF failure...though just a WAG ).. and cleaning the maf doesn't do much.

either way, the improvement in both my idle rpm as well as the performance of the car has been astonishing. i think the bmc, while allowing for greater air flow, was creating some kind of a "leak" which in turn was causing my idle to "hunt" up to 1000 then down to 750rpm.

changed the maf and back to stock filter ( with a a cut airbox still ) and no more issues, and the car is smooth in its power band delivery. it used to have rough spots but i can always tell when the MAF is failing. it's very subtle.. at first. also, i'm using the $47.00 MAF's from ebay. same part, just i think it's recycled with a new diode. stock mahle filter. hope that helps a bit. between throttle body and maf, i think you're on the right path. good luck.

 

I wonder, I know that BMC's come with a light oil on them right? Do they need to be washed like the K&N which has also been known to cause these problems?

 

Yeah, they sell a "cleaning kit" but that's as scientific as it sounds. I think the bmc comes pre oiled and needs cleaning. Mine was beyond cleaning and I opted for the OEM since the power gains are either negligible or not worth the maf related issues. Also, I'm convince that higher HP tt's blow mafs when we hit he rev limiters. They get fried. At least I think they do.
I never had these issues with my stock x50 car.

 

i picked up a brand new one on ebay for $43 works great!

 

Do a full pull in third gear..from 2000-6700rpm....maf reading should be 1000-12000..under 100% actual throttle value.....if its outta all over place, then u might have a bad MAF and hesitation under full throttle. A cleaning will help a dying Maf but not fix it.