Very New To Ford

It sounds like the upstream o2 sensor would be a good place to start if you are confident its a fuel issue. I'm not experienced with the 3.8 but the o2 sensor(s) tell your ecu if the car is running rich or lean and the ecu adjusts the trims accordingly and they don't kick in until they are warm. Is your car throwing a check engine light? it could honestly be several different things like the maf, fuel pressure or charging system. I'd reset your ecu by unplugging the car for 5min after you try something to reset your trims.

+1 on above. To add look for vacuum leaks.

Realbill1976 said:

But im gonna learn my mustang from front to back, top to bottom.

Click to expand...

If you are serious about learning AND you really want to fix your car then there's a tool that could make very short work of this problem. An ODB2 scanner. With an ODB2 scanner you could "ask" the PCM the values for things such as:

• Fuel pressure
• MAF flow
• O2 switch rate
• DTC codes
• Long term fuel trims (LTFT) and short term fuel trim (STFT).

You would be surprised how much having this information will change the trouble shooting process.

Don't have an ODB2 scanner? Think they are too expensive? Here's some information on an affordable Windows based ODB2 scanner.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

While your at it.Take a look at the PVC valve & wire screen under it.Old dirty one on Rt.(even after soaking overnight) And, New replacement on left.