SloopJohnB@mac.com

crosspost..here's some info on MAF sensors:

http://forums.quattroworld.com/s4s6/msgs/20442.phtml

johnkk

I had a MAF go bad and the problem only appeared when the engine heated up. Even opening the hood, cooled the temp enough to eliminate the misfiring. Did you have the hood open when the problem cleared?

Gsrob

That's exactly what I am experiencing. At first I thought it was the mileage that made it start misfiring but I see a correlation between the oil temps and misfire. Today I drove it to work to see if it would pop any other codes and/or misfire much. After driving 15 miles to the interstate (and running beautifully) it started misfiring when the temps rose to around 225F. I don't notice it, even at 200F which is normal for lower speeds after warm up in my car. I will say that after running it to operating temps and then letting it sit and idle, it usually takes 5-8 minutes of sitting stationary before it begins to misfire.

Side note: I re-checked the codes today upon arriving at work. I really hoped I would get at least either bank info on the misfires or individual cylinders but still don't. The only new code is for Bank 1 Side 1 O2 circuit malfunction.

Since it's a random misfire code with no specified cylinders, it seems more MAF related though, right?

Gsrob

Looking up options for the MAF Sensor replacement... It looks like both Bosch and Hitachi are similarly priced. Will I see a difference in either of the two if I were to replace it? Also, Pierburg (apparently the OEM Audi MAF that is made by Hitachi) can be found for around $140 as well. Anyone have a recommendation before I pull the trigger?

Also, if I were to unplug the MAF when experiencing misfiring at idle, would it prove that I needed a new one or would it be inconclusive?

Gsrob

Update... I ordered the Hitachi maf on Amazon for $118... It should be here tomorrow evening and I'll install it to see if that was the problem. In other news, my b1s1 o2 sensor code came back on today and included a bank 1 lean code.... Any chance the pre cat o2 could have been causing this whole mess?

Gsrob

Thank you to sloop and the other posters. I got my car back on the road with a little bit of effort. Turns out the whole problem was due to the faulty pre cat o2 on the passenger side. I ended up ordering an NGK o2 with factory connector and put it in in like 30 minutes. I thought it was going to be significantly harder due to the angle but it wasn't bad at all to route the wiring and remove the old one. Old maf ended up being fine and I am returning the Hitachi to Amazon. It turns out a faulty pre cat sensor can screw the ecu big time causing lots of random misfires.

indoor

Can you tell me a few details about removing the pre cat O2? What kind of wrench? Lots of heat or just engine warm(after a long drive, etc.). I know I have the same problem. I tried to loosen that same O2 and it wouldn't budge. I used some PB Blaster, and the car was cold. The wrench I used was a 'claw' wrench like this one

Gsrob

No problem... First of all I had the car completely cold. It haven't been driven that day. I had the same type of wrench attached to multiple extensions that put the ratchet just above the valve cover. Standing from the driver side I was able to get the most leverage on it with a 3/8 ratchet. I did not use any solution like pb to soak it at all. It would've been significantly easier to break loose if I had a longer ratchet to use but I didn't. If you find you're having a hard time breaking it loose, you may been bumping against the exhaust shield. There is very little clearance and the wrench can only be turned like a quarter turn at the most each time before it runs into the manifold shield. I was lucky enough to be able to get my hand down there once it was loose and just spin it out by hand.

indoor

Update :
I went back to try and remove the passenger front O2 sensor. I put the 'claw wrench' on the O2 by hand and tried to spin it to get it into a good position for the 1/4" extensions. But the wrench kept spinning by hand. I had a scare thinking I stripped the nut on the O2. It turned out the O2 sensor was loose. I must've loosen it last time I worked on it, and the wrench stopped in the screw on the down pipe. It's tight and dark down there so I didn't notice that screw the last time. Yet it seemed there should be about an inch of clearance before the wrench hit the block. So for anyone trying to remove the passenger front O2 sensor, look out for the down pipe screw that might be getting in the way of loosening the sensor.

Anyway, after I changed that O2 sensor, my car has been CEL free and the fumes odor is gone...I have yet to check if the mileage improved after the next fuel up, hopefully it did

Gsrob

Awesome man, glad to hear it. Yeah, there are several things down there that can be bumped into when trying to spin the o2 wrench. For me, it was the exhaust shield. Like you said, I had about a little under an inch to spin before needing to reset it again.

Anyway, hopefully your car stays CEL free!