MAF unplugged = car runs better WTF??

[Zach L]

The engine is a COMPLETELY stock '06 2.0T FSI, including factory air box/engine cover.

I've been experiencing a hesitant, rough idle for several thousand miles as well as a CEL. My first thought was coilpacks, but I figured I'd change the plugs before taking it in for the recall. After changing the plugs I started the car back and it idle PERFECTLY. Ran it for about 10 minutes then when I went to shut the hood I noticed I had [unknowingly] left the MAF unplugged.

When I plugged the MAF back in the car leveled off at idle, but it was back doing the bumpity idle as before. I restarted, took it for a drive, restarted several times more and the idle continued to be bumpy. I unplugged the MAF again and it ran smooth as a baby's ass again.

So WTF is it? The ECU must be reverting back to a base air/fuel map or utilizing different sensors when the MAF is unplugged. So, bad MAF?

[ThumbThumbs]

My guess would be a bad maf sensor.

[ed_gti]

Do you have a code from the CEL?

[DeathB4Dishonr]

do you experience rough starts as well? ie taking a long time to start or turn the key, no luck turn again and it fires up kind of rough?

[nashbar]

intake leak, vacuum or charge.

[Zach L]

Originally Posted by ed_gti

Do you have a code from the CEL?

I was gonna wait until I get back from vacation to purchase a VAG-COM ...no money at the moment. I have some friends in Houston w/ VAG-COM but that's 3 hours away and I don't have the time. The bumpy idle has been around MUCH longer than the CEL

Originally Posted by DeathB4Dishonr

do you experience rough starts as well? ie taking a long time to start or turn the key, no luck turn again and it fires up kind of rough?

I had that problem back when I was in warranty, but they replaced a few fuel system components and the problem was corrected. I was experiencing the same rough idle as I am now, but there's no hesitation to start with this problem, just the bumpy idle.

Originally Posted by cybershot

if you need a MAF, i have a spare for ya. They are quite expensive from the dealer

Sweet ...you mean like the whole engine cover/airbox?

Originally Posted by nashbar

intake leak, vacuum or charge.

What do you mean by 'charge'? How would any of these be overcome by unplugging the MAF?

[GodSquadMandrake]

Yeah it could be a vacuum leak, charge would just be it leaking under boost.
It could also be a bad MAF sensor. Diagnostics would help a lot on this one.

[07Noside]

if you have a boost leak or vac leak the car is seeing x air going into the motor at the MAF. If it is leaking after the maf the a/f mix will not be correct. If you unplug the maf the car switched to map based mode and reads air quantity and calculates the amount of fuel to be delivered by the pressure in the system. The map sensor is mounted on your throttle body pipe. so if the leak is before there and after the maf this is why unplugging it would help.

Also like its been said could be a faulty maf but best way to try without diagnostics on hand is swap mafs with a buddy real quick and see if the problem still persists.

[lextildeath]

If unplugging the MAF helps the situation, it is usually the MAF sensor itself. Well, at least on MAF-only vehicles without additional MAP sensor, such as my 1998 Volvo C70.

[HereticByDefault]

Originally Posted by Zach L

Sweet ...you mean like the whole engine cover/airbox?

The MAF sensor is only screwed into the whole engine cover/airbox. You can separate the sensor from the engine cover.

I wonder if mine is bad...I've been getting a pretty annoyingly rough idle for almost the whole time I've owned the car. I've gotten a couple of unexplained CELs, but they've all cleared themselves.

[Zach L]

Originally Posted by 07Noside

if you have a boost leak or vac leak the car is seeing x air going into the motor at the MAF. If it is leaking after the maf the a/f mix will not be correct. If you unplug the maf the car switched to map based mode and reads air quantity and calculates the amount of fuel to be delivered by the pressure in the system. The map sensor is mounted on your throttle body pipe. so if the leak is before there and after the maf this is why unplugging it would help.

Also like its been said could be a faulty maf but best way to try without diagnostics on hand is swap mafs with a buddy real quick and see if the problem still persists.

That does sound logical ...the bumpiness is only at complete idle, so it'd have to be a vacuum leak if it were one of those. The thing is I'm seeing the same exact boost/vac reading I've had for the 3 years I've owned the car.

Is it possible for the leak to be substantial enough to cause a slightly bumpy idle, but still insignificant enough to not register any difference on my boost gauge?

I think it's humorous how I've been running a boost gauge on a stock GTI for 3 years, but it's the one thing I wanted on the car right off the bat (for reasons such as diagnosing problems such as this one). With all the PCV and DV problems out there I don't know how some of these guys can run a chipped car w/o a gauge.

BTW, thanks for all the responses and help guys, it's much appreciated.

[BoostedS]

I have an 09 GTI with 6000 miles and Ive noticed a bumpy idle since I bought the car at 180 miles. now its way worse, feels like the car is going to die. but the RPMs dont move, and no CEL's. I haven't checked with the dealer yet but Im sure they're going to say nothing is wrong. They recently replaced the 02 sensor due to a CEL. forgot to mention my car is completely stock.

[John/Cue\Publik]

VW MAF sensors can be had for as little as $80 if you don't mind buying an a1 cardone reman, usually special order at the O'Reily's or autozone. the above mentioned price is for a rabbit MAF at O'Reiley's

[TSSSI]

Hi @ all....

I have the same problem with my chipped 1.8TSI... with MAF it is running much rich and I have some missfires... without MAF the car is significantly faster... I dynoed with and without Maf and I have 243 BHP with 372nm with MAF and 239 BHP with 380nm without MAF and never had any missfire without MAF!!!

see the dynos... left is with MAF, right is without MAF




and here both...

[GodSquadMandrake]

^
Ever heard of closed loop mode?
At WOT the ECU ignored the MAF and oxygen sensor and runs preset fuel tables.

[TSSSI]

but why it runs without MAF better in midrange???

With MAF I have an AFR of 10,4:1 from 2000rpm to 7000rpm.

without MAF I have AFR 11,4:1 from 2800-4500 and then AFR of 10,8:1 from 4500 to redline!!!

[Zach L]

I agree ...at WOT the engine is running a preset map.

I really need to buy an VAG-COM, but I just can't cut it right now.

Anyone in the Austin area have one?

[GodSquadMandrake]

Originally Posted by TSSSI

but why it runs without MAF better in midrange???

With MAF I have an AFR of 10,4:1 from 2000rpm to 7000rpm.

without MAF I have AFR 11,4:1 from 2800-4500 and then AFR of 10,8:1 from 4500 to redline!!!

I don't know. Obviously the MAF is doing something there.

[Zach L]

Today I found out the car is misfiring on cylinders 1,2, and 3. Spark plugs were replaced about 2k miles ago. Stealership appointment tomorrow @ 9am for coilpack recall.

If the coilpacks WERE the cause of it all, how would unplugging the MAF make a difference?

[projectquick]

OP have you cleaned the MAF? Maybe some how the wire got dirty and with it unplugged it reverts to a preset fuel table. It can't hurt and the can of MAF cleaner cost like $2.99

[Zach L]

Originally Posted by projectquick

OP have you cleaned the MAF? Maybe some how the wire got dirty and with it unplugged it reverts to a preset fuel table. It can't hurt and the can of MAF cleaner cost like $2.99

No I haven't tried that. My plan is to borrow a MAF from a local if possible, to see if it's responsible for all of this.

[TSSSI]

Originally Posted by GodSquadMandrake

I don't know. Obviously the MAF is doing something there.

it is not a leak in the intake because... if it is a leak than it would read less g/s at MAF and than it will run lean, but with maf it runs to rich