A couple of different things come to mind if the new tps doesn't help. The 200 - 300 rpm change at highway speed could be attributed to the torque converter unlocking and that CAN be triggered by the tps, however, unless some weird mechanical thing happns inside the sensor, it can not report an inaccurate value. There are only three possibilities. It can read the correct value based on the physical position of the wiper as it sweeps across the sensor's resistor. The signal wire can be grounded on a bare spot on the engine or body, typically on a sharp metal bracket. Or, ... The wiper can momentarily lose contact with the resistor due to dirt or a piece of the resistor breaking off. A "pull-up resistor" inside the computer will force the signal wire to go to 5.0 volts if there is a break in that wire or in the sensor. You can prove this to yourself by measuring the voltage on that wire when the sensor is unplugged. The only voltages the computer will accept as legitimate are between 0.5 and 4.5 volts. When it sees the forced 5.0 volts, it knows there is a problem, will memorize the appropriate diagnostic fault code, and will turn on the Check Engine light.
When the computer sees an abrupt or rapid change in voltage from the tps, it instructs the torque converter to unlock for a few seconds thinking you're about to stop or you are headed for rapid acceleration. On some systems now, a problem has to act up for a long enough period of time before it will set a fault code. The glitch may be not long enough for that to happen, but it is long enough for the torque converter to unlock. That would explain the surging ay highway speeds but not at idle. The torque converter will not lock up when the engine is cold or when vehicle speed is below 40 - 45 mph. If you see the tach jumping at 55 mph with the engine warmed up, the torque converter HAS to be unlocking.
If the surging occurs at idle, it would be more typical of a vacuum leak. Use a squirt bottle to spray water in the intake gaskets and vacuum hoses while the engine is still cool. If there is a leak, you will see the water get sucked in and the engine speed will slow down. Another clue to a vacuum leak is the cruise control won't work smoothly or will lose speed on hills.
Saturday, May 29th, 2010 AT 3:41 AM