Rough Idle

[chogeberg]

I have a 94 ranger that I just replaced the head gaskets on and it was ruining rough at idle. I replaced the fuel filter and drove it to work for the last week and half. The truck averaged a little over 21mpg even with the rough idle. Yesterday I replaced cap rotor and plugs and it smoothed out the idle a little bit. I then test drove it about a mile and by the time i got back the truck would not idle at all and was getting O2 lean codes. I replace the O2 sensors and now the truck is idling worse then ever. Does anybody know what I should try next. The Fuel pressure to the fuel rail was around 40 when i check it after the fuel filter change.

 

[4.0B2]

clean the mass air flow sensor.
check for vacuum leaks.
what's your plugs look like?

 

[RonD]

Yes, unplug MAF and see if idle changes
http://www.therangerstation.com/tech_library/CleanMAF.html

Also run some Seafoam in the fuel tank to clean up the injectors

Yes, good MPG would mean a leaner mix that is not good for the engine.

Does it still idle higher when cold than after warming up, so IAC(idle air control) and ECT(electronic choke) are both working as they should?

 

[chogeberg]

Cleaned MAF and IAC and it idles considerably better but still rough. Checked for vacuum leaks and did not find anything. Not sure where to go from here.

 

[RonD]

The MAF should be on the air filter box, make sure the air plenum between the MAF and intake is not cracked or broken, or the Vent tube if it has one isn't plugged or cracked, that's the hose that runs to the valve cover or oil filler.
Extra air coming without passing the MAF sets a leaner mix.

Try puling out the air filter and putting your hand over the air intake, restricting it, if idle smooths out you have an air leak somewhere.

How old are the spark plug wires?
And did you use motorcraft plugs?