I have just put a 87 350 TPI into my s10 with a painless wiring harness and it starts but wont idle runs for 2-3 second and thats it..
please help!!!

 

What did you use for a fuel pump?

 

Try to start it without the MAF sensor connected.

 

I used a stock IROC fuel pump for the 350

 

unplugged MAF and it runs for a couple seconds longer bu thats it, if you the MAF plugged it will run while you have your foot on the gas a bit.

 

I think the most important thing to do is verify that the engine is in proper timing. Try putting it between 6-8 degrees btdc. Have you reset the throttle position sensor to .54 volts? You could also try disconnecting the idle air control valve and starting it. Just a few guesses. Lots of things can cause that sort of starting and dying, or a combination of little things.

Make sure all vacuum hoses are in place as well, you don't want leaks before the MAF/throttle body. There are a few hoses at the rear of the plenum that could leak, as well as a sensor located in the bottom above the egr, or a couple hoses in the throttle body. Runner leaks could also cause this if they are severe enough.

 

Can you check fuel pressure? With a guage hooked up, start it and make sure the pressure don't drop off as it dies.