tach freak out and car shut off

[beav147]

alright i have a 95 tsi all wheel. all of a sudden my tach would freak out with the RPM jumping from 2000 to7500 to 4000 then back to idle. if i step on the gas it would do it again. it only happens when the car is warmand it throws the check light. it read cylinder missfire and censor circuit malfunction. i know that would technically narrow the problem down to electrical but a ecu shouldn't have to warm up for it to malfunction. any suggestions would be great.

 

[luv2rallye]

The tach signal comes from the ignition power transistor so that would be a good place to start especially since your also getting a misfire code. Bad power transistors can sometimes malfunction with temperature.