1994 ford ranger with 4.0 v-6 engine 137k miles Idle is rough and engine light is on. Hissing sound under the hood. Engine wants to die if it sits at idle too long. It seams to smooth out at higher rpm. Plugs, ignition wires, fuel filter and air cleaner have all been changed recently. Fuel injector cleaner added to gas approx. every 2-3k

SOURCE: 1993 Ford Explorer idles rough when engine is warm

try changing distributor cap & coil

SOURCE: 1994 ford ranger extended cab 6 cyl fuel injected 2 wheel drive automatic

This year of ranger had a few flaws, In one case, a break power booster was robbing the vacumm, you can test this by plugging it off and seeing the differance, but you will have limited brakes. This model year had a problem with a vacuum leak on the manifold. You can check these in many ways, but please don't use starting fluid. The rear of the manifold usually on the drivers side where it seals to the block.
Also, in 2 other cases a cracked head has gave me the same problem. It is caused from a loss of vacuum.

SOURCE: 2005 Ford Escape Rough Idle - engine code state lean fuel mixture

I recommend getting a repair manual from an auto store for your vehicle. They run $15 to $20. It will tell you exactly how to do everything you asked and also give you the values that should be expected. Hope this helps.

Ned C Cook

• 3433 Answers
• Posted on May 15, 2009

SOURCE: my ford ranger idles low and spits gas out the exhaust

Hello,
First confirm it is either gas or eastter. Wayer/condedste collects at the tail oip as a byproduct of the caralyctic converter on cold rngine It normally occurs on firts start of a cokd enginw. the ebgine idles low because it is col, but should reyutn to normsl after warm uo.. If for sure iys gasolinem and the engine runs eiygh, then angihector is bad, good luck. I hope this helped yyou

SOURCE: Hissing sound from engine & check engine light on

sounds like an intake manifold gasket leak.