I just bought a F150 1992 5.0 L V8 302 Engine.
I changed Spark Plugs, Oil and Filters, runs smooth really smooth at Highway, but at Idle speed seems little unstable. I took it for Emissions test and HC PPM at Idle are too high (1600 PPM)and at 2500 RPM emissions are really nice. This confirms what I see on driving.
Where do you think is trouble located? Timing adjust?

Thanks in Advance for any ideas

 

I would pull trouble codes and see if that gives you any idea. Since fuel/air mix is OK while running, but not at idle, could be the TPS making it run rich at low RPM's.

 

What is TPS ??

 

TPS stands for Throttle Position Sensor. It is a riostat that sits on the bottom of the throttle body and sends information to the computer on how far the throttle plates are open to regultate fuel/air mixture. Should be .5-1.0 volts with the throttle closed and 4.5-5.0 volts when open and a smooth transition in between.

 

Ok thanks now is clear for me.
I just checked and found vacuum hose disconected, do you think this can cause trouble??