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.

[JAAY]

Grrrrrrr... Runs like a tiger Sounds like MAF and I would do all four O2s. Happened to me years back and this seemed to fix all the issues. See you Sunday.

[Boxtaboy]

Originally Posted by JAAY

Grrrrrrr... Runs like a tiger Sounds like MAF and I would do all four O2s. Happened to me years back and this seemed to fix all the issues. See you Sunday.

Haha...yeah..growls like a tiger.

Check your email Jay. I'll be giving an update on whether or not the drive is still on. Right now, it looks like the weather forecast says showers, so I may postpone to another date. Stay tuned.

[landrovered]

"P1128, a long-term, fuel trim lean code. Any unmetered air introduced into the engine can cause P1128 to set. Tips: Carefully check for vacuum leaks. Include all areas that might introduce unmetered air to the engine. Don't forget exhaust leaks before the O2 sensors. "

Found this, perhaps it might help your troubleshooting.

[boxzilla]

I recently came up with a code: 1128/1130 indicating a lean mixture and failing o2 sensor in bank 1/post cat. The addition of fuel addatives may "trick" the o2 sensor ....you might try swapping your bank1 and bank2 o2 sensors to see if the fault follows the sensor. Either way, I just replaced mine at 70k miles as that appears to be the failing point for these sensors. Welcome to CEL Hell!

[Boxtaboy]

Haha...thanks guys, for the suggestions. I will definitely try to further isolate those issues IF the darn light comes back on. Right now....no light, no do anything.

Just thought it was weird that it would not show up again for 1000+ miles when I really didn't do anything to change the car's setup. Could an 02 sensor recover from failure? LOL

[landrovered]

I would not point to a bad 02 sensor without other codes. This could be related to the secondary air injection system. I have seen problems in the SAI cause this code. Exhaust manifold gasket leak could do it as well.