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I have a 2003 Pontiac Grand Prix, 3100 Engine, 160,000 Miles. Recently during acceleration I noticed the engine would hesitate, and started acting VERY sluggish (no power on the gas pedal). Shortly after that started, it began to hesitate at shift points (reaching 4000 RPMS and not shifting until I let up on the gas pedal). I also noticed during acceleration that it would start 'jumping' and feel like it was slipping in and out of gear (however it felt like the RPM's were dropping out when it slipped, not spiking).
I first dropped the tranny pan, drained the old fluid - replaced the filter (old fluid was brown) and then replaced the pan with a new gasket, and new fluid, including 1 Qt of Slip Stop. Almost immediately after, the check engine light came on. Went to Auto Zone, was told the 1st o2 Sensor was bad, and the fuel cap was bad or there was an air leak in the gas tank. I replaced the o2 sensor (Pre-CAT) and they cleared all the error codes.
Since doing that, the 'power' is now back during acceleration, however once I hit a constant speed it will still become 'jumpy' (and I went ahead and manually accelerated the throttle body while in park, I reved it up to a higher RPM, and it became hesitant - so I know its something else besides the tranny alone). But the shift points while accelerating hard are still not working, but when acceleration is easy, say from a stop sign, it works a lot better.
I cleaned the MAF sensor, I cleaned the PVC valve, I checked to make sure the throttle body was cleaned and not sticking, I cleaned the intake. I have no error codes and yet it still hesitates and is sluggish. Any ideas??
I first dropped the tranny pan, drained the old fluid - replaced the filter (old fluid was brown) and then replaced the pan with a new gasket, and new fluid, including 1 Qt of Slip Stop. Almost immediately after, the check engine light came on. Went to Auto Zone, was told the 1st o2 Sensor was bad, and the fuel cap was bad or there was an air leak in the gas tank. I replaced the o2 sensor (Pre-CAT) and they cleared all the error codes.
Since doing that, the 'power' is now back during acceleration, however once I hit a constant speed it will still become 'jumpy' (and I went ahead and manually accelerated the throttle body while in park, I reved it up to a higher RPM, and it became hesitant - so I know its something else besides the tranny alone). But the shift points while accelerating hard are still not working, but when acceleration is easy, say from a stop sign, it works a lot better.
I cleaned the MAF sensor, I cleaned the PVC valve, I checked to make sure the throttle body was cleaned and not sticking, I cleaned the intake. I have no error codes and yet it still hesitates and is sluggish. Any ideas??