Need some help guys... getting so frustrated over this. Naturally, I don't have the kesh (or time) to drop this thing off at BMW and say 'call me when you're out of parts to replace' but I'm mechanically inclined and even my indy is having difficulty with this one...
Codes first popped up back in November. If I remember correctly, I had lost my non-ethanol gas station (they caved under pressure) and I poured in 2 cans of Berryman's Fuel System Cleaner using a tank of cheap (WaWa convenience store 93 octane). Just shortly after that, codes appeared. Prior to that, it was June of 2009 when I fixed my issues (detailed on this board) by replacing an after-cat O2 sensor in addition to an extensive 60K service which I also ended up replacing all 2 pre-cat O2 sensors and 1 after-cat. That was 45K miles ago.
So ever since then I've been sticking with Shell VPower 93. I've taken it to the indy and they pointed out that I had a torn elbow in the air intake boot. I I also remembered from my saga a couple years ago that one of the 1 after-cat O2 sensors hadn't been replaced. So I had them replace that - nada. So I ordered the intake boot, some belts (needed doing) and a new Mann air filter. They also pointed out a valve cover leak on the lower side near the exhaust. I also cleaned the MAF with CRC MAF cleaner when I installed the air filter. In addition, when I replaced the air boot, I pulled the throttle body and IAC and gave both of those a good cleaning but it didn't seem to get rid of my codes. Cleared the codes and it came right back within a days worth of driving (approx 26mi).
Took it back to the indy, and they did a smoke test on the intake - no leaks. They hooked it up to the GT1 and did some diagnostics as well as attempting to update the DME software but it was already updated. They pulled the plugs and noticed I was using the NGK Iridiums and suggested I use the NGK originals. They also said that these codes are typically associated with the MAF sensor failing. So I ordered the MAF, a valve cover gasket, a set of NGK original plugs, new oil and filter and coolant for a drain and fill. I also did a brake fluid flush as it had been 2 years since I did it last.
Codes the indy returned were BMW:
235 - Pre-Cat Bank1, Fuel Trim
236 - Pre-Cat Bank2, Fuel Trim
So after taking it back from the indy, the codes were cleared by them. THey stayed off for 2 weeks and 2 days. On the 3rd day is when I decided to do my work. I did the new MAF install, valve cover gasket, oil and filter change, coolant drain and fill, brake fluid flush, power steering fluid extract and fill but I hadn't done the plugs. After doing this work, the following day of going for a drive, the check engine light comes on.... I hadn't taken it back to check the codes but I assumed it was the same ones. So I swapped my old MAF back in and sent the new one back. I was eager to recoup that cost...
Needless to say, at that point, I was clueless as to what caused the CEL to come on with the NEW MAF, air intake boot and VCG after 2 weeks of being code-free. I should mention that while doing all the work, the battery died so I had to trickle charge it for an hour or so to get it to crank over.
So then I decided to tackle the plugs. I replaced the Iridiums with the original NGKs and torqued to 23 ft/lbs and used anti-seize paste on the threads. The codes did not clear on their own even after a few tanks. The 45K mile NGK Iridiums appeared normal but on the rich side where there was darker soot and what appeared to be very fine particles clinging to the the surface. I compared it to a few sites online and it appeared normal but leaning towards rich.
So I was gearing up for a long trip. The morning of, I said - what the heck - and picked up two new pre-cat O2 sensors. I drove approximately 500 miles and the light came off (two separate tanks of gas from two separate stations and brands (Gulf & Sunoco) and stayed off for another 100 miles. You can imagine my jubilation at this stage. Then it returned a few miles after stopping to fill up with Sunoco.
It stayed on and has been on up until now 300 miles after that fill up. I should also mention that on this 1000 mile round-trip from eastern PA to Toronto through Appalachia, with the wife and kids and some luggage loaded up as well as the AC on the whole time, I averaged 21.3MPG cruising @ 80MPH 85% of the time which I thought was respectable.
Today I took it to AutoZone and had them pull the codes and it's displaying:
P0313 - Misfire detected, Low Fuel
P1093 - Pre-Catalyst Fuel Trim Too Rich Bank 2
At no point during my journey did I let the gas go low. It was always halfway between quarter & half tank when I filled up.
At this stage, I thought I'd covered all my bases but I'm leaning towards actually purchasing the MAF again and seeing if it alleviates the problem but reluctant to do so.
Any insight or advice would be greatly appreciated.
