Help troubleshooting low idle
 

Hi folks,

I bought a 83 F250 with the 351 automatic. The engine runs great, but idles really low. I'd like some help troubleshooting it. The guy who sold it to me said he's 100% sure it's a vacuum leak.

Here's what he said. It was idling fine. Then one day he ran out of gas. He said he kept trying to start the truck but both fuel tanks were empty. After a while he put in a couple gallons of gas and got it started. Ever since then it's been idling really low.

The idle needs to be fixed because it shakes the truck pretty bad.

Any suggestions on how I should fix this?

Thanks!

80skeys

More details:

it idles FINE when in Park or Neutral.

It idles very LOW when in Drive or Reverse.

I adjusted the idle screws out ... no improvement.

I sprayed some starting fluid in the area behind the carb and beneath it. Truck idles up for a couple seconds, then back to low idle. ... Vacuum leak?

Yeah sounds like a vacuum leak

If there is a leak, the solvent will be drawn into the engine and the idle speed will suddenly change and smooth out for a few seconds.