do you have a aftermarket air filter on it? if so do you have the right adapter? if you block the MAS it can give improper reading's and wont let it idle at all you can just take off the filter and try starting it... not saying that's 100% sure fix but i had that happen to me once, i grabed to wrong filter addapter out of my part's bin LOL it took me about 15min to find that one LOL but give it a shot it cant hurt