I had the timing belt replaced last week in my 96 LS400 @ 150K miles (90K miles after original replacement @ 60K miles). I also had new plugs, distributor caps and rotors, and fuel filter installed (already run K&N air filter). Since then the car runs fine, but my check engine light has popped on 4 separate times, each time with code P0171, System Too Lean, Bank 1. I've already replaced both O2 sensors on Bank 1 side within the past year, so I doubt this condition involves them.

Has anyone experienced this same issue? If so, what was the cause for the code? The car's going back to the tech this Friday for diagnosis - I'm hoping it's something as easy as he left a vacuum line off.

Any advice/recommendations would be greatly appreciated.

Thanks

Most likely, your MAF sensor is dirty or need replacing. First step would be to clean the MAF with a dedicated MAF cleaner such as CRC or an electronics cleaner. Spray on the sensor wire, but do not touch it. It's screwed into the air intake with 2 screws and connected to a wire harness that you unplug. Quite possibly it became contaminated when the tech had the intake off.