I recently got myself a 1990 z28, and when the motor gets hot,(starts at about 110 degrees) with the car in gear and my foot on the break, the motor surges. ie comes real close to stalling when i hit the gas. i checked it for vacuum leaks with a smoke machine and nothing. when i bought the car, someone took out the t-stat, and wired in a switch for the fans and it had rusty water in it. i flushed in both directions with a machine, put in a 195 t-stat, and took out the switch. it dose not over heat at all. useing the snapon motise, o2 voltage is 398mV even without the motor running. i ran a new wire from the o2 sensor to the ecm and put in a new ecm. that is the extent to what i havwe done so far. i am new to this old school stuff. i'v only been a machanic for 2 and a half years. has anyone ever seen a problem like this, and can anyone help me out? it would be apreciated.