my 73 f100 390 runs rough at idle, stop light etc. give her the gas on the open road lots of power and preforance. When you shut her off she likes to keep on running almost always. Had the carb adjusted and timing didn't make any difference. I suspect it needs a vave job. Had one done years ago, and the the motor went bad, replaced it with a short block. Shortly afterwards this started. Haven't put many miles on it since. Any ideas would be helpful. Love the forum, you guys are great.

 

Two small things that could cause this are too much initial timing or too fast an idle speed. Also a Vacuum leak might do it.


Bear Tracks

 

timing, mixture, idle speed. maybe it's running too slow or fast

 

Yes, I would agree with the above. I just found out my EGR valve was bad and causing my engine to run rough at idle or not at all. Ok when I gave it the gas. I blocked it off and it idles like it is supposed to. I don't know if 73 trucks came with an EGR valve or not. Just a thought.

 

Mine does have an egr valve. I also noticed what appeasred like a drop of oil coming from under the intake manifold. I will sure check it out and let ya.ll know. Thanks

 

Hi,

I've had the problem for some time. It seems it idled even worse when it was warm. Replacing several cracked vaccum lines seemed to aleviate the problem. Adjusting the idle mixture helped some before the vaccum problem was identified.

 

From my own experience on my 300, run on (on my rig) is from either idle set to fast / choke sticking or a vacuum leak. A vacuum leak will cause the engine to run like crapola at a stop sign.