For the first 5 minutes or so after the car is started I get lean tip-in and overall leaner AFRs (~13) when in boost. Doesn't matter if the car is cold or warmed up. After 5 minutes or so the fueling becomes very consistent with no lean tip-in and boost AFRs around 12. Car also intermittently goes into open loop mode around 10" of vaccum with AFRs around 11.5. Just recently, also intermittently while crusing in vacuum, AFR's will cycle off scale full lean for a couple of seconds before settling down.

There are no CEL's to give me clue. I've replaced the front O2 sensor, plugs, wires and coil pack. I'm thinking possibly the TPS is going bad but looking for some recommendations. Thanks.

 

PC Pro?

 

Sounds like a fuel delivery problem. Pump, relief valve, filter, etc