Truck info: 2004 fx4 stepside 4.0 automatic. 79,700 miles

I bought it used from an older gentleman in december of this past year, he had driven it less than 5000 miles the whole year. Since I got it, the gas gauge has never worked. I can fill it up and it will read empty, then between 20 and 100 miles later it will kick to full anf travk back down to 1/4 tank.

I have done 3 oil changes at 3000 miles since then. The past week I've noticed when it idles around 1100 rpms both at start up and warm. And it is rough when it does, shakes the whole truck a little. 2 days ago it threw a check engine light. I had it read and i dont remember the code but it was 2, one was sending unit high output voltage, I dont remember the other but it was related to the sending unit. When I had new tires put on i asked them to read the codes, they did and wiped them. Told me I needed a new sending unit. Im wondering if there the sending unit is causing the idle. Or could it be plugs and wires, or fuel filter? Trying to avoid the sending unit @200 plus bucks if i can fix it with a 5 dollar filter.

thanks all

 

Filter is $12 and change it just because its a 2004


Here's the thing about Check engine light(CEL) and codes
There are literally 1,000+ codes
Guessing is worse than not having them at all, so you don't have the codes, lol

WRITE THEM DOWN next time, they can be very helpful, and what is also helpful is when you know the EXACT code number you can then look at the similar codes that the computer DID NOT USE which helps eliminate possible causes for the code the computer DID USE.

High idle warm, and rough running is usually a Vacuum Leak
4.0l SOHC Ranger had a common issue with PCV hose elbow air leaks

Good read here: https://www.ranger-forums.com/4-0l-o...mon-cel-93776/

To check if you do have a vacuum leak
Warm up the engine, drive it for 5 minutes or let it idle for 10 minutes
Let it idle and open the hood, unplug the IAC Valve's 2 wire connector, what it looks like is here: How to: IAC valve cleaning thread (w/pics) | Ford Explorer and Ford Ranger Forums - Serious Explorations

IAC Valve sets engines idle, so when you unplug it the valve inside will close and idle should drop down to 500RPMs or engine may even stall, either is GOOD!!
It means no vacuum leaks
If idle stays high then you DO have a vacuum leak, and that's causing the high idle and rough running

And a vacuum leak will cause computer to set LEAN codes because there is too much air coming into the engine