I have a 2000 ranger with the 3.0 L first it was back firing in the intake and exaust so I changed the map sensor, it cured that . it runs rough and I am going to change the plugs as well.... I just bought this truck. it has a lean code on sensor 1 p1131 it runs horible at cold start up and smooths out after warming up, but will idle rough and die... at hhigher rpms it runs but still i feel it missing. I am thinking plugs and and cleaning the fuel injectors...

 

Check for vacuum leaks... plus the pcv valve rubber elbow

 

Welcome to the forum

Yes, put some Seafoam or similar injector cleaner in the gas tank

Yes, new spark plugs are a good idea if you are not sure when they were last changed

2000-2002 3.0l Ranger did have a batch of bad Coil Packs, Ford used to have a range of serial numbers to check but can't find it any more

Unless you got receipts for past work you are basically starting from scratch as to whats been serviced and what hasn't

You don't have a MAP sensor, you may mean MAF sensor

Also change ECT(engine coolant temp) sensor if engine doesn't do Choke mode well, runs poorly until it warms up
All cold gasoline engines need to be Choked until they warm up, the ECT sensor tells the computer when to Choke the engine and how much choke to apply
Nothing to do with temp gauge on dash, that's the engine temp sender

P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1
Bank 1 is passenger side of V6 engine
Upstream means the O2 closer to the engine
(Downstream is the one after Cat Converter, just FYI)

So if you only get the one Lean code that would mean either a lower intake gasket leak, a misfire on that side or that O2 sensor is worn out

So I would fix your misfire first and see if code goes away

If not then how many miles on the vehicle?
Upstream O2 sensor last 125k or 10 years, then they start to go Lean
2000 Ranger should just be on 3 set of upstream O2s, or at the end for the 2 in there now

Downstream last longer as they "see" clean exhaust after Cats


And just FYI, lean code does NOT mean engine is running Lean, it means computers calculation for fuel was lean so it had to add more fuel than it expected to get the O2 sensor in correct range
So if it is an O2 sensor issue then engine is actually running too Rich and its costing you money because of lower MPG, new upstream O2 sensors will pay for themselves in MPG over the next 125k miles or 10 years

Codes rarely mean what you think they do, lol, the definitions are written in mechanic-ese, a certain expectation of how engines operate and these computers "think" is assumed

 

Yes I meant maf sensor , and I changed that...it's a 2000 ranger 4x4 with 3.0 240,000 miles... and looks great, no rust and was well taken care of... the pcv looks like original equipment, so i replaced it.... it was stuck and full of grime. .. checked over and over with it running and spraying starting fluid with no increase in rpm's ... no air leaks, double checked hoses, spark plug firing order and change plugs and wires...I have it where it will at least idle and drive with very little power, and yes it's burning fuel like crazy. I added lucas to the tank when I had
it home from the car lot, that couldn't even get it to start....I bought it for 450.00... they were over trying to start it. I am going to change the front o2 sensor, temp sensor and see what that does to it...thanks for the advise by the way...!

 

Change BOTH front O2 sensors
240k its time for the 3rd set up front

Poor MPG plus poor power and lean code can also mean exhaust is getting clogged up
You can test for that with Vacuum gauge on intake