I have a 2005 Soft Tail Fatboy 96 in. I installed a Thundermax Autotune and a heavy breather air filter. I watched the official installation video numerous times and followed the written instructions to a "T". At first start-up the idle was extremely erratic. The first ride (approx. 10 miles)...my bike stalled 9 times...idle was not right...speedometer went nuts...stuck at 120 mph then back to zero when I was riding at least 45 mph...very weird.
Does anyone have any idea what is going on?

 

I would reinitialize the Thunder Max again. Mine was acting up after I had discontented the battery. Same type of issues with the speedometer. Once I ran through the initializing sequence everything was fine.

 

Does the Thundermax have a separate connection that goes into the throttle position sensor? I had the same problem whe I installed a different tuner, same symptoms. I had bent a pin on the TPS. I straightened the pin re connected and problem solved. I don't know if this helps good luck Thundermax a lot a $$$.

 

No. Thundermax replaces the stock ECM and uses the stock ECM cable.