88 454 Running Rough under part throttle

[85DualBox]

Hello,
recently purchased an 88 R30 with 454 tbi. I drove it home for 10 hours, no issues, running great. As I drove it to my storage spot, It started not taking part throttle and throwing a Service engine soon. Today I drove it for the first time in 2 month and it is running terrible. Idles nice and sounds good just off idle. Then breaks up, running rough, no power. When flooring it, it kinda clears up and takes off.
Code is 44 O2 lean. It smells awe fully rich and actually backfires out of the exhaust, so I am thinking it is trying to compensate for a lean condition which is not present. That’s why it clears up at full throttle. So one have some insight?

 

[MarineOne]

Hello,
recently purchased an 88 R30 with 454 tbi. I drove it home for 10 hours, no issues, running great. As I drove it to my storage spot, It started not taking part throttle and throwing a Service engine soon. Today I drove it for the first time in 2 month and it is running terrible. Idles nice and sounds good just off idle. Then breaks up, running rough, no power. When flooring it, it kinda clears up and takes off.
Code is 44 O2 lean. It smells awe fully rich and actually backfires out of the exhaust, so I am thinking it is trying to compensate for a lean condition which is not present. That’s why it clears up at full throttle. So one have some insight?

Replace O2 sensor sounds like it's clogged

 

[fast 99]

O2 data may be skewed from misfire. Could be ignition or a mechanical issue. Backfiring in exhaust, I would put a vacuum gauge on it first. Broken valve spring, flat cam, or other valve train issues are possible. Then proceed to ignition.