I just got the 305 TPI in my '86 IROC replaced with a Jasper Class 2 performance 350 including a hypertech thermomaster chip, 26# injectors, new accel distributor & coil, new EGR valve, new catalytic converter, new IAC. It runs great, but idles very rough and stalls if not in neutral or foot on the gas & brake at the same time. It will crank but won't start when hot. The shop that installed it can't figure ot out.

 

Maybe here's the issue. What was the chip for? You are out of the point where it will work. I can't remember what 305s came with but 350s came with 22 pph injectors. If your Hypertech was set for 305, there would be a definate problem. If it is set for 350, it would still be a problem. The ECM was told that it had 22 pph injectors and it has determined that a certain pulsewidth for those conditions based on 22pph. You have increased it by 18.18% (26-22)/22 is the equation. You will have to switch back to 22 pph or get a custom eprom to get it running right. Feel free to ask Eileen Formato at www.fasterproms.com for her opinion. They will custom one for $500. It will be roughly set to your specs then you datalog it and send the file to them. Takes a couple of burns till they get it just right. If you make major mods in the future like a set of heads, different cam, induction, etc (not thermostat or new coil) it costs $150 for them to get it right again. I have used their service and liked it.

 

i believe the 305 had 19lb. he's right the injectors are to big for the hypertech chip you have.

 

I finally got some time yesterday, so I put in the old fuel injectors (19#) just to see if I could get it to idle properly. The was no change in the idle, so injector size doesn't appear to be it. Any other suggestions?