CEL. Stumped.

[Boxtaboy]

Ok, let me know what you think of this...

1600 miles and several months ago, I got my first ever CEL go off on my 01 Boxster. It has 62k miles on it now. I bought a code reader and read the code (P1128)- only one code, which pointed to a few possibilities: vacuum leak, exhaust leak, bad 02 sensor, etc. All I did at the time was throw in a bottle of Techron in the tank and cleared the code. The code did not return for 600 miles or so.

When it returned, I decided to look into it a bit further, and opened up the engine bay. Nothing seemed amiss except that I did see some oil residue in the area of the oil fill tube. Figured I had a cracked oil fill tube that caused a pressure drop and thus, the CEL. Was about to order a new oil fill tube to install during the Spring, but while I was in the engine, I cleaned the MAF, and reinserted, and then cleared the code again, and again, threw in another bottle of Techron.

The code has not returned for over 1000 miles now. Seems as if the problem just went away on its own. The only thing I really did was clean the MAF and throw in some Techron. But, the P1128 code itself doesn't usually point to a bad MAF. So what gives? Could it be that I put bad gas in the car? Reason I ask is because both times I got the CEL, I had gas from this one gas station that I no longer go to. Oh, and both times when I got the CEL, I was just stopped somewhere and idling.

I was going to replace my oil fill tube, but now since no CEL, I figure why fix when no codes present. Oh, and engine is not running funny... no jumping idle, no misfires...runs like a tiger.