My 261 with TBI from a 91 astro van with the 16144288 ecm and 5.0 throttle body runs fine with stock chip. It sounds like you have a vacume leak or a bad IAC. How does it run after you go closed loop ? is your O2 sensor in the exhaust from 3 or all 6 cylinders ? I'm running a 195 theromstat wich shows about 180 on my new tempature gauge and a heated O2 sensor. The unheated sensor would drop it out of closed loop at iddle.
