Battery Guage Moves back n forth when idle n truck shakes

[JeremyGonzales]

I recently purchased a '94 ford ranger 4.0 liter manual transmission. When idle the truck seemed to have a slight rumble or shake to it,so after about a mnth i decided to do a basic tune up. Changed the oil,air filter,replaced spark plugs and spark plug wiring. Gapping is to be between .052-.056.I gapped each spark plug to .054 and replaced them one at a time to avoid any confusion. Once i finished,i started the truck and it seemed to have done the trick. The slight rumble/shaking while idle was no longer present and it ran great. I parked my truck for a few hours and once i was ready to go for a drive i realized the rumble/shake was back, and when idle, the battery guage seemed to be moving back n forth,headlights flickering as if wanting to turn off. There was also black smoke w a bad smell coming from the exhaust. Any idea of what this may be? Once the truck gets going it can cruise great,but the trouble is once its idle. Im trying to correct this problem a.s.a.p. so ide appreciate anyones opinion or feedback to help me resolve this issue.Thank You.

 

[JeremyGonzales]

possible vaccum leak???

 

[Big Jim M]

I'd start with another temperature sensor for the computer.. Might be stuck on cold and not allowing the engine to get the proper tuning for hot running..
Big Jim