Transmission

There are three common things to consider. The first is using the wrong type of transmission fluid. During partial lock-up, special additives prevent the lock-up clutch from chattering. To identify that, when the shudder occurs, hold the accelerator pedal perfectly steady, then briefly tap the brake pedal with your left foot. That will cause the lock-up clutch to unlock for two or three seconds. The shudder will stop occurring during that time.

The second is a misadjusted brake light switch. If it vibrates enough to switch on the part that is an input for the cruise control and lock-up clutch, it can cause intermittent unlocking. That unlocking will last a few seconds which feels quite different than the shudder.

The third thing is a dirty throttle position sensor. They are fed with 5.0 volts, and the output signal varies between 0.5 to 4.5 volts. The voltage has to fall outside that range to set a diagnostic fault code. Specks of dirt can cause it to develop the wrong signal voltages but that are still within the acceptable range. Near idle, (approx. 0.5 to 1.0 volt tells the engine computer to unlock the torque converter in anticipation of coming to a stop. At wide-open-throttle, (approximately 4.0 to 4.5 volts), the computer will unlock the lock-up clutch to double the torque for more power.

The problem with this type of TPS problem is it usually does not set a diagnostic fault code, and when viewing the voltage on a scanner, the glitches occur too quickly to see. Sometimes you can make a short recording on the scanner, then play it back slowly later. Normally we do not approve of replacing random parts, but this is one case where the part is relatively inexpensive and popping on a new one is a good test.