Sounds to me like it could be a sticking EGR valve. With the engine warmed up and running
at around 2,000 RPM, pull the vacuum line off the valve and watch the diaphragm, it should
fully close.

The EGR recycles exhaust gasses back into the combustion chamber under certain conditions
to lean out the misture - generally while fully warmed up at highway speeds. It is not supposed
to operate while the engine is cold and/or idling but they sometimes get carboned up inside and
stick open.

The valve lookspretty much like this:




It fits on a plate between the intake manifold and carburetor and the diaphragm should be behind the carb:

 

I have the EXACT same problem as you, I'd post symptoms but they are verbatim to yours. The difference is mine is a EFI. I have replaced the EGR valve, the IAC valve, the fuel filter, spark plugs, the throttle positioning sensor, cleaned my intake manifold, seafoamed my intake, replaced the 02 sensor as well. None of the those did jack. Its been a month and a half and several hundred dollars. I leave for college in 5 weeks and I have a truck that doesn't stay running, would love to hear what y'alls opinions are.

Thanks

 

hey guy check the egr valve maybe stuck open

 

I had a similar problem awhile back...

My truck would start fine and idle alright, but as soon as I dropped it in gear, it would not hold an idle. I had to keep my foot in it to keep it running. Same with driving it around, it shook and ran rough.

Turns out it was due to worn out spark plug wires. I guess they leaked voltage or were just not letting enough power to the plugs, because as soon as I installed new wires and fresh spark plugs, it was as though I had a whole different truck. Fast idle was better, it would maintain a nice low idle in park -and- in gear, and it ran as smooth as silk in gear while driving.

 

This entire thread is from last May-July, I would imagine he fixed it or crushed it by now.

 

...didn't see the date. Whoops. lol

 

Mines currently sitting in the driveway torn down the heads checking the fuel injectors. If my life savings wasn't in this truck it would be crushed

 

Replace the distributor cap and rotor

Mine was not used often and the rotor was corroded.

As soon as I replaced it the rough idle was fixed

 

Mine ended up being a faulty MAP sensor. Firewall, left side. It's about 3 x 4 x 4 box with a vacuum line going to it. Try taking the vacuum line off. It might be hard to start (the purpose of the thing), but once running, it should smooth out. Not very expensive either...

 

Man, it amazes me sometimes how people don't read threads.... I'll say again, this thread is
from last May-July and econobox hasn't logged into FTE since then, I'm sure he's figured
something out by now....

 

Well, if I had this problem start up with my truck, I would like to read all the input people would have to say no matter what time is was logged on. I guess people just like to help.
Merry Christmas

 

great info in this thread, awesome resource, thanks guys.


just bought a nice old 83 bronco with this same dying when you press the brakes issue. nice to know there is a place to pick up some tips to help me fix my new ride. I was guessing vacuum leak of some sort but I'll know more tomorrow when I do the tune up and check it all over... al