Just replaced motor in my 2008 ranger sport 4x4 4.0. Idles fine in park but when put in gear or when i come to a stop it spitters. I replaced iac and maf still doing new plugs wires and the rest of the jasper kit any ideas

 

Welcome to the forum

I assume an Automatic transmission

When you shift out of Park the computer should get a signal from the DTR(digital transmission range) sensor, it is on the shift rod/linkage on drivers side of transmission

When computer gets the "in gear" signal it should bump up the idle(IAC Valve) by 50RPM
Is the idle RPM going up?

Vacuum leak
After engine is warmed up, and idling, unplug the IAC Valves 2 wires, IAC Valve will close all the way
RPMs should drop to 500 or engine may even stall, either is GOOD, it means no vacuum leaks
If idle doesn't drop then you have a vacuum leak

A vacuum leak makes for higher idle but engine will idle smooth, when you put engine under a load, in gear, then vacuum leak will cause stumbling until you add more fuel, step on the gas pedal