I have a new to me 1995 Tahoe with 5.7 motor and 4L60E transmission. The car has 157,000 miles on it and appears to have been well maintained. When the drivetrain is up to normal temperature the vehicle will maintain freeway speed (70 mph) but will not accelerate much past that point. If I floor the accelerator pedal the transmission will drop from OD to 3rd and the revs will jump to about 2500 and just sit there. If I keep the pedal down the car will not accelerate. It runs smoothly at all throttle positions, but it will not accelerate.
I've also noticed this behavior in lower gears, where the engine will rev up to a point (usually around 3000 rpm) and just sit there without upshifting. If I back off the accelerator just a little bit the transmission will upshift and the cycle repeats.
Stuff I have tried so far: The engine was running too cold (around 140) so I replaced the thermostat which corrected that issue. The fuel mileage was really bad (about 8 mpg) so I guessed it was running in open loop mode and replaced the front coolant temperature sensor. That improved the mileage to about 12 mpg. Today I pulled and checked the EGR valve and it was pretty clean and working normally, with no diaphragm leakage. I also did a manifold vacuum test at idle (saw 20 inches) and 2500 rpm (saw 18 inches) to see if there was an exhaust system blockage issue.
This is an ODB I vehicle and there are no codes and the check engine light is not on. Where do I look next? I'm thinking perhaps throttle position sensor or O2 sensor?
I've also noticed this behavior in lower gears, where the engine will rev up to a point (usually around 3000 rpm) and just sit there without upshifting. If I back off the accelerator just a little bit the transmission will upshift and the cycle repeats.
Stuff I have tried so far: The engine was running too cold (around 140) so I replaced the thermostat which corrected that issue. The fuel mileage was really bad (about 8 mpg) so I guessed it was running in open loop mode and replaced the front coolant temperature sensor. That improved the mileage to about 12 mpg. Today I pulled and checked the EGR valve and it was pretty clean and working normally, with no diaphragm leakage. I also did a manifold vacuum test at idle (saw 20 inches) and 2500 rpm (saw 18 inches) to see if there was an exhaust system blockage issue.
This is an ODB I vehicle and there are no codes and the check engine light is not on. Where do I look next? I'm thinking perhaps throttle position sensor or O2 sensor?
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