I had the VAFCII SC for 4 years and work fine until last year. I start to have a miss of power randomly especially under very light load, with no Cel ever. The ECU love to get into the open loop mode and dump a lot of fuel from my simple Air/fuel Autometer gage.
I have changed O2 sensor, cleaned fuel injectors and works fine for 3 months. Then, it starts to miss a lot more like no spark for 2 sec. Maybe too rich and kill the ignition??? I start to trim down the fuel using VAFCII in open loop mode.
I have changed the thro sensor and map and no help. It still randomly miss. At a point, it stalls at idel when i lift the thro in netural. Then i found out tighting the gas cap can redue to chance of stalling the engine when lifting the thro. RPM will not dip down too much with no loading. Something related to fuel tank back pressure.
Lately, it won't run correctly under cold start. It miss and shake until warns up.
I am chasing my tail and please help!
Is it about the fuel line and pump or FMU???

John Chan

 

Tune

 

I would say unhook your vafc disconnect the battery while you change the spark plugs and possibly the coil packs... connect the battery and see what it does without the vafc hooked up. If it runs good then re-connect the vafc and get a tune.