Hi, everyone. I'm new to the forum and could really use some help. I recently purchased a 99 Ranger that was in need of a tranny. Put a new tranny in and the entire time I've a rough idle and it runs rough at low rpm's (2200ish and lower). I'm getting the codes p0171 (bank 1 lean) and p0301 (cylinder 1 misfire). Can't seem to track it down. Here's a list of my attempts so far: decarb and fuel injection cleaning service, new fuel filter, cleaned maf, tried unplugging maf to see if it change and it didn't change at all, checked for vaccum leaks, new coil, plugs, and wires. Any kind of ideas or assistance in anyways helps. Oh, also the once I get passed around 2200 it smooths and seems to drive fine but it's gutless at all rpm ranges. Thanks in advance.

 

Did you clean out the idle air control (IAC) valve?

 

just trying to find if theres something else that could be causing this. im planning to check the plug gap and cleaning the injectors in the morning. any help would be appreciated. thanks guys and gals

 

Welcome to the forum

When you have a misfire, in this case #1 cylinder, bank 1, and then a Lean code on the same bank, the Lean is because of the misfire, not the cause of the misfire
So ignore the Lean code, it will go away once the misfire is fixed

Lean and Rich codes come from O2 sensors
O2 sensors can only see Oxygen, not fuel
Lean code means higher oxygen in exhaust, Rich code lower oxygen in exhaust

When a cylinder fires the fuel AND the Oxygen are burned up
When a cylinder misfires no oxygen is burned up
That oxygen goes into the exhaust, O2 "sees" it and Lean code is set

If Lean code is set BEFORE any misfires, or on a different bank than the misfire, then it would indicate a different issue

So not a chicken or egg thing, if you have misfire and then a Lean code, Lean code is NOT a symptom/cause, its a normal result of having the misfire

I would do a compression test on all 6 cylinders, first
Compression is good or bad, no middle ground
Burnt/leaking exhaust valves are most common cause of loss of compression on all piston/valve engines
So best to take compression off the table first, or find out it is the reason for the misfire so you don't waste time and money on non-fixes

Your description of rough idle and smoother running at higher RPMs fits the loss of compression scenario, at higher RPMs there is less time for compression to "leak out" low enough to cause misfires

No reason not to clean gap or replace spark plugs, that's just normal maintenance, but if that doesn't help the misfire then do the compression test next