I have an 87 bronco 2 thats runs good then couple of min it will sputter only goes when I step hard on the gas does any one know what it could be

What have you replaced so far to try and fix the issue?

air flow sensor

I would try to do a full tune up. Cover the bases. Plugs, wires, fuel filter, air filter, PCV. Spray down the throttle body with cleaner. See if that cures the sputtering.

this is everything I have replaced. fuel system, firing system, egr, bypass valve, complete distributor, ignition module, ignition switch, map sensor, o2 sensor. The engine is a new crate motor, I thought I had a intake leak so I replace the whole top end. it run really bad when I first start it up and when I let it idle it will idle up and down like a lope and eventually it will die.. it will run good when it is warm but every time I start it back up it will start to sputter 10 seconds after I start it up then stop after a few min. I was thinking maybe it is getting air in the fuel system. just wondering this bronco has alot of money in it it was my dads so I have to finish it to be restored. any help will help thank you.

What size engine do you have in it?

2.9 v six. standard trans

is the fuel pressure as recommended

Firing order is right on and timing is right on? Have you loosened the distributor and just tried to hand time it by ear to see if it will run better? Check out this thread. Sounds like this guy has same issue as you......... http://www.hotrodders.com/forum/will-engine-run-all-if-its-180-out- 95885.html

1-4-2-5-3-6 clockwise.

it's the curse! i have recently got a 86 broncoi ii,a hell of a deal ,i thought, it has fuel,spark won't start, then it will,started and ran so good i tried to drive on road it went 2mi started sputtering and stopped,trailered home did nothing and now it runs like a top but have not been on road yet,big prob for us theres not a cure yet

If you start it and let it idle in the driveway, will it eventually die?

having the same issue with my 88. From hours of reading it is going to be one of these two things, ECT or ECM.