Idle is a little funky

[Warren 86 ranger]

sometimes its perfect and other times it jumps up goes down back and forth from 750 to 950 then back down to 750 so an an so forth whats could be causing this

86 ford ranger 2.9l 5 speed manual electric 4x4

 

[jhammel85]

The ECU in the early years of the 2.9 do this for somereason. My truck does this too. I consider it somewhat normal.

 

[RustedRanger]

Mine did that. Partly from a bad idle air control valve and partly from a bad plug-in for the coil. My friend put a diagnostic computer on mine and found that when the plug-n was jiggled the idle did the same.