I recently bought a 1990 F150 with a 351. It is an automatic. The first question I have, is what is the correct RPMs for the idle? It idles around 500-600 RPMs. The second question is when I put it in reverse after running it for a while it will die. If I put it in reverse just after I start it, there is no problem. Other than that, the truck runs great, no noises or other problems, I'm just kinda new to Ford and 8 cylinder engines. Any help would be appreciated.

 

Normal idle is about 750.
The stalling in reverse is normal happening at times.
Has been going on with these trucks since 85 efi. Don't have a soluton to it.
In your case, the idle is to slow and aggravates it.
I would remove the IAC and clean it with throttle body cleaner, then spray clean the throttle body holding the throttle fully open.
Use up the whole can and spray all around the bore.
Let it set 10 min. before starting because the engine may not start from the cleaner, right away.
Next is to be sure the ignition timing is at 10* inital with the SPOUT plug removed, then replace the plug.
This needs to be done so the computer does not change the timing while your setting it by turning the distributer and you get it accurate.

 

Thanks.