87 Bronco II will not idle

[emt304]

I have a problem with my 87 bronco II 2.9L. It will idle very rough. It will go up to 2000 rpms and then start loping from 500 rpms to 1500 rpms and then cut off. If you keep your foot on the gas and start driving it will hesitate for about 3 minutes and then straighten up. When you go about a mile and stop it idles perfectly, but u can cut it off and restart it right back up and it idles rough again. It shows no codes and iI have checked all vaccum lines. What sensors would make it do that?

 

[Earl43P]

Let's rule out a fuel pressure problem by priming the system before each start:

Key to Run, listen to Fuel Pump prime for 2 sec, key to Off.
Repeat 3X, THEN crank it over, see if it idles good, drive off.

 

[emt304]

Already ruled out fuel problems, already replaced distibitor, wires etc.

 

[IMenriched]

Already ruled out fuel problems, already replaced distibitor, wires etc.

So what kind of fuel pressure are you getting? What were the readings?
What has been done so we don't suggest things that were already covered.

Believe that Earl43P was heading you toward was that you might have a bad FPR ( fuel Pressure regulator)
Have you ran codes to see what has been tripped??

It maybe a faulty relay...or bad grounds/connections
another place to check is the IAC,(Idle Air Control)...remove and clean, dry and replace

 

[emt304]

fuel pressure is 40 psi. I replaced the IAC but it didn't help. I am leaning toward something to do with the vaccum, because it seems after it builds up a good vaccum it idles perfect and then when i stop the engine and restart it within 2-5 seconds it loses the vaccum and idles rough untill it builds up vaccum. Could I be on to something? Could it be EGR, MAP sensor or some other sensor that has vaccum lines connected