Continuing Check Engine light P1128

[trauh]

I have a 2001 C2 Cab with 16K miles on. The check engine light went on around 7 weeks back with a P1128 code (cylinders 1-3 too rich). It since been reset and reoccurred three more times.

So far I've followed Loren's advice and checked for an obvious exhaust or intake leak and have come up empty. We did find a the air intake on the throttle body to be a wee bit loose. After all that it has reoccurred again.

Here is the situation. I always occurs on the highway in heavy traffic, when the car has been moving slowly (10-25 mph) for a few minutes. Its been top down every time (I know, shouldn't matter, but hey, I'm covering everything). Outside temp has ranged from upper 70's to upper 90s.

It does not seem to repeat every time the car is under these conditions. But it has only occurred moving slowly on the highway. I'm thinking of trying some fuel injector cleaner tomorrow, any maybe pulling the fuel filter (though that doesn't seem likely to me given the mileage and slow speed circumstance). Any thoughts?

[Loren]

P1128 code (cylinders 1-3 too rich)

No, P1128 is: Oxygen Sensing Adaptation Area 2 (Cylinders 1 . 3) - Rich Threshold

This means that oxygen sensing at rich threshold is stored in the memory, this means that the fuel/air mixture is too lean. The DME can not compensate for the lean mixture by making the mixture more rich - it is at it's max rich threshold and still the O2 sensor says it's too lean.

Since you do not seem to have a P1130 (cylinders 4-6) then that would imply that there is an air or exhaust leak on the 1-3 cylinder side. Could be as simple as the oil filler cap (o-ring) or as bad as the oil separator.