I would assume, given your information, that if the engine speed sensor is bad, that it could have a broad effect. The ECU has no reference for IP timing, and it would also explains why your AC isnt working. The ECU needs to modify engine RPMs to compensate for the additional load, so if it doesn't see a consistant RPM reading to begin with, the ECU does not know what RPM to adjust to. I may be wrong, so if anyone else can help more have at it.
1994 Golf GL 1.8T 318whp 284ft/lbs
1999 Golf GL TDI TDIHeater GTI Heated Leather RC3 Sprint520s