TUNE UP??? Im doing it on my 400E this week. I didn't think I needed one till the other day I pulled the Caps and Rotors off for the helluv it. Geez, were they disgusting! If that doesnt fix it...how's his wiring harness look? Mine's destroyed too causing the external fans to not come on and overheat in idle. Wiring harness also contains injector wires, maybe causing hesitation? There really could be many things causing this. Just something to check out! Let me know what yall find out, always interested in 400E problems!