I have got a 2000 (A33) Maxima with a VQ30DE. Recently it has developed an issue where when the car is throttled in P or N to about 1.5k RPM, the engine revs start to pulsate uncontrollably. When driving in D from a standstill on slow acceleration, the car accelerates normally then at about 1.5k RPM it shifts from 1st gear into neutral, REVS the engine to about 3k and then slams into second gear all on its own.

I have tried replacing the Throttle Position Sensor, MAF and even cleaned the throttle body but the problem has not been rectified. The OBD scanner did not throw any fault codes but it flagged an issue with the transmission control module and that had been rectified ( turned out to be a transistor on the TCM that was not functioning and got that bit replaced).

The car also tends to "misfire" at low speed low throttle scenarios and idle at standstill in D: e.g crawling in traffic the rpm suddenly drops an returns to idle. But this does not happen in Neutral.

Has anyone ever experienced such issues and can suggest possible causes and solutions to rectify?

PS: I can't head to the local Nissan dealer for them to diagnose because my car was an import.