1995 Audi A4 transmission control

at a guess I would say that following the engine replacement, the vacuum line to the auto transmission actuator was not reconnected
check all wires and connections to the transmission

Transmission control code. Take it to your dealer or a transmission shop you trust, unless you are a competent DIY transmission person. Can be minor or not.

Speed sensor as in transmission like VSS Audi doesnt use on or RPM sensor as in the engine, Or wheel sensor for ABS Audi does use it is it for transmission or engine of wheel speed for ABS

463A definitely not VAG codes they are from one of the cheap code readers.
Audi A4 Quattro - fault code 463a: engine control unit disabled.
This could be a dirty sensor or bad connection somewhere.
The immobilizer light flashes when you insert the key?
Imobiliser pick up loop in the steering column sounds dodgy, take the cowling off & check its connected ok. Just clipped it back in.

If you plan on doing more than light tuneup work, I highly recommend purchasing a manual for your car. We have for each of three vehicles a Haynes manual and it contains all the details on maintenance possible for the shade-tree mechanic. All are based on a complete rebuild.
Audi A4
Even if not doing a particular job, one can somewhat estimate what it will cost to have done.

you're looking at over 2k in expenses but ebay would be your best bet

Hi, the sensor on the engine (right at the rear end of the cylinder head) has two separate outputs. One drives the temperature gauge and the other provides data for the engine control unit. The output for the engine control unit is almost certainly faulty and the sensor will need to be replaced. It isn't an expensive item and's not time consuming to replace (1/2 hr) - so you could ask Audi to do it for you when they replace the ignition coils.
Hope that helps Matt..

Greetings!

Yes, the engine mounts and bell housings are the same.
The swap should be straight forward, however be sure to swap all the vaccum controls and emission system from the 2.6L.

Have fun!
Cheers, Jay

Fist thing to do is change the transmission fluid and filter. Audi says the transmissions have lifetime fluid, but that's bull - change it first and see if that helps. If not, have the car scanned by a shop and have the chassis codes looked into. If there's a true electrical control problem, there should be at least one code stored (which may not trip the check-engine light).

Could be a transmission issue. Did you hit any objects while driving ? Have you performed a visual inspection under your vehicle ? Have you checked to see if you have any loose vacuum hoses ? Any codes in your engine control module or transmission control module ?