Ranger showing lean codes rough idle

[Scpc]

Hello all I have 97 4.0 ranger 4x4 that has been running rough for a while now.
Symptoms are:
Rough shaking at idle
Low power when going up (can’t make it up steep hills)
Poor MPG getting 9-11
Sometime takes a couple tries to start

CEL is on shows p0171 and p0174

I have upper and lower intake gaskets done
PCV replaced
IAC replaced
TPS replaced
MAF replaced
New coil pack
New plugs
New wires
New fuel filter
Did a at home Smoke test only saw some smoke coming out IAC cap which seems to be ok from what I’ve seen?
EGR tube replaced
Throttle body replaced
EGR valve replaced

Not sure what to where to go next. Could certain parts that have already been replaced just be faulty?

When I take out the IAC the truck dies

Tested fuel injectors by holding pedal down and try to start but truck would not start.

I’m no mechanic just a college kid who doesn’t mind getting dirty so any advice would be appreciated

 

[rusty ol ranger]

Does it run better when the engine is cold?

If so it kinda sounds like an O2 sensor took a shit

 

[Poppa_R]

From my experience those codes say the engine is running lean. That ususally means there is unmetered air entering the engine bypassing the MAF. Since you have replaced everything that would effect this, I would try spraying the intake manifold with starting fluid. If the intake is leaking than the rpm will rinse when the fluid is sucked into the engine. The bad Oxygen sensor is a good idea that was stated by rusty old ranger. Also when ever I had to clear codes I always performed a keep alive memory erase.

 

[Scpc]

I feel l Iike It runs the same cold and warm sometimes it runs better when it’s warm sometimes worse.
Would it be a safe bet to replace all o2 sensors????

I’ve cleared codes a few times same issue stays. I’ve sprayed brake cleaner around the intake as i has some laying around but no change in the rpm.

 

[SenorNoob]

Guessing you got low enough to soak the lower intake? That's where the 4.0 usually leaks or at the plastic intake tube.

If it's O2 sensor related, you should be able to clear the memory and get it to run ok for a couple minutes from cold. It takes that long for the O2 sensor to warm up enough to start switching. The low MPG could be caused by the PCM dumping too much fuel because it thinks that bank is lean.

 

[Scpc]

I can spray down there again when I have the chance, I did have the upper and lower intakes gaskets done about a year ago but I’ll give it a double check. Is there a way to test o2 sensors without buying new ones???

Appreciate all the input

 

[rusty ol ranger]

I can spray down there again when I have the chance, I did have the upper and lower intakes gaskets done about a year ago but I’ll give it a double check. Is there a way to test o2 sensors without buying new ones???

Appreciate all the input

Yes you can unplug them and test voltages when hot and cold. I cant remember the voltage specs offhand though

 

[Poppa_R]

If I am not mistaken the lower intake manifold gasket is under the valve covers.

 

[Scpc]

I’ve sprayed all around the intake and didn’t have any change in rpm. If I bought a scanner with live data, could I use that to narrow in on the issue?

 

[Scpc]

Did another smoke test hooked up through the pcv intake and smoke only came out iac vent and by the intake before the maf and the air filter. Should I do a compression check or check for an exhaust leak???