Jason H

Here's a refresher on the story from my post on Sat:

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1 year and 10 months in my 2000 1.8T with no problems, just out of warranty (thanks to long commute) and now...

Yesterday I noticed that the car didn't have the kick that it did before, especially in 2nd and 3rd where you really notice the chip (GIAC). It definately wasn't in "limp" mode, in fact it still felt stronger than stock, just not up to it's usual chipped performance.

I needed gas so I went to my usual 76 station and made an even higher blend of 100/91 than usual, probably about 94.5 octane (usual is about 93-94). I get back on the freeway and about 3 miles down the road I get a CEL. Drive real cautious the rest of the way home. I have vag-com, but my laptop battery was dead. While charging it I searched the archives here. Amoung the remedies was checking the gas cap. I think "****, why didn't I remember that!" So I go out and I'll be damned it twisted to the left pretty easy. So I turned it until I hit 3 or 4 clicks. About a half hour later the laptop was charged and I hooked up vag-com. The DTC throwing the CEL was:

<b>17536 Fuel Trim Bank 1 Mult, System Too Lean 35-00</b>

I cleared it and did a throttle adapt for good measure. Then I took the car out for about 15 minutes. Not only did the CEL not come back the power was back too. Ok, hunky dory. I figured that the throttle must have gotten out of adapt, hence the power loss/return. and that the CEL was just my moronitude at the gas station.

I drove the car around a lot today and all still seemed well (I even checked for DTC's [none])untill I was in my parking lot at home. Then as I was parking the damn CEL came back! This time I hadn't noticed ANY loss in drivability before it came on. I still had the laptop in the car so I fired up vag com again and it is the same DTC. Now, yesterday I didn't remove the gas cap before screwing it tighter, I just turned it until it clicked. maybe I didn't reengage the seal?

So there it is folks. I'd like some input. Is it likely to be residual symptoms of my loose gas cap, or was that just coincidental. Research here points to the MAF or less likely, the O2 sensor if there is an actual physical problem. What measuring blocks can I run specifically to get a stronger diagnosis of where the problem is. If it is the MAF am I screwed since I'm (1,500 miles) past warranty? I've taken out and held the MAF from James R's car, so I know it's changable by myself. But how much does that bitch cost and does anyone know the calibration routine? If it's the O2 sensor, how hard is that to get to, and is that bux or not? ANY advice/experiences welcome.
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On Sunday James R was kind enough to lend me a hand. Since Sat. night the CEL HADN'T returned, so we used VWtool, VAG-COM and OBDtool to scan the car and do some driving testing. The first thing we did was check the voltage for the O2 sensors. We went to a relatively long stretch of road and into 3rd and 4th we shifted early (low revs) to hold the car at WOT for as long as possible. We had already determined that at idle the voltage seemed normal. Bank 2 sensor remained reasonably steady while bank 1 sensor moved like a sine wave hunting between rich and lean. Here are the results as graphed by OBDtool for my car, and then the same test in James':

Mine:
<img src="http://www.queenky.com/jasonh/cel_debacle/101501_obdtool_me_02.gif">

James:
<img src="http://www.queenky.com/jasonh/cel_debacle/101501_obdtool_jr_02.gif">
(OBDtool could't fine the bank1 sensor1 on his '01, but recorded the sensor 1 type values from sensor"2"!)

Mine is not really sinificantly lower at peak than his. Hmm.


The second test was to hold the cars rpms(in neutral) as steady as possible at 2k and 3k and measure the lb/min of airflow at the MAF.

Mine:
<img src="http://www.queenky.com/jasonh/cel_debacle/101501_obdtool_me_maf.gif">

Mine:
<img src="http://www.queenky.com/jasonh/cel_debacle/101501_obdtool_jr_maf.gif">

Again, relatively similar. (Thank goodness, that damn MAF is expensive!).

In fact since we couldn't trip a DTC or get the CEL back, the only oddity we found was that the readiness code for the catalytic converter(s) said "failed or incomplete" and I had driven 3 driving cycles sine the last throttle adaptation. For an extra measure of protection I swap back in the stock ECU just until something conclusive is found or not found wrong.

Cut to this morning. After driving about 10 miles on the way to work I pulled over and checked everything again. No DTC's, and the readiness now looked like this!:

<img src="http://www.queenky.com/jasonh/cel_debacle/101501_readiness1.gif">
They ALL show passed now!

So out of curiosity I do the same O2 sensor test as before and this is the result:

<img src="http://www.queenky.com/jasonh/cel_debacle/101501_obdtool_me_stk_o2.gif">

A little lower peak, but this was the stock chip, and it's still well above 800. Now it gets weird again. Car still feels fine with no DTC's, but only 5 minutes after the last readiness check they look like this:

<img src="http://www.queenky.com/jasonh/cel_debacle/101501_readiness2.gif">

Did the parameters of the test cause these failures or did this prove something is wrong? I drove the rest of the way to work and shut the car down a couple more times at lights to add driving cycles. by the time I got to work they had all passed again except the Secondary Air Injection:

<img src="http://www.queenky.com/jasonh/cel_debacle/101501_readiness3.gif">

Well that's where it stands. I know this is an absolute <B>BOOK</B>, but engineers like a lot of data before drawing a conclusions. If any of the forum members can offer any further insight, I'd be very happy. Since this is all so flaky I'd like to hope it was just all an anomaly, but I'd like someone with some technical know-how to help restore my peace-of-mind. Thanks AW.