Installed a 358 in place of a 305, it is an '86 maf tpi and ecm. Has the 19# injectors, stock prom, and Comp Cams 262* Extreme Energy cam with S/R Torquer heads. The idle quality is real poor! Sometimes it idles ok and other times it dies. Have to drive with one foot on the gas and one on the brakes. The car runs great above 750 rpm's. I replaced the IAC valve, helped slightly. Haven't found any vacuum leaks. What are the possible solutions to fixing this? Thank you!

 

Anybody?

 

I had the same problem on my '95 Astro. It was my CPI (fuel injection unit). It is easy to test. All you need is a Fuel Pressurer gauge that goes to 100psi or what ever yours calls for. Hook it up to the shreader valve. Turn the key 'ON' (don't start), you should have whatever pressure it calls for, if Not it's your fuel pump in the tank. Turn key 'OFF', it should Hold pressure, if Not that is your problem. You have plug up the return (smaller line) and test again, if it holds it's your fuel pump, if it drops, it's your fuel regulator or injectors leaking.

 

Have you checked the timing? That can mess up the idle, as well as if you installed the distrubutor 180* out. I have dont that before and took me a while to figure out. What it really sounds like though, is an exhaust leak. I am currently dealing with an intake leak and it does the same thing to my idle.
Good luck tracking that down, I hope you find it.
Mike