2001 Ford Taurus SEL DOHC Cylinder Misfire?

My 2001 Ford Taurus SEL s check engine came in and flashes when idling. I ran a code on it and it is a cylinder 5 Misfire P0305. I changed the spark plug, didn't work. Changed the spark plug wires, didn't work. I just changed the coil pack and it to didn't work. What else could it be? Is it time to throw in the towel and take it to a mechanic. Before I forget to mention, yes I erased the codes after each fix and it came right back on and went right back to rough idling. The code reader I used was a plain Jane one you can borrow from advanced auto.

Might have an intake manifold leak that's affecting that cylinder, or worst case scenario, burned exhaust valve.

Does it has spark and fuel at # 5? What is the # 5 spark plug condition look like? Injector? Compression reading? If you suspect the valve train: A leak down test would prevail…

Pop the valve cover and see if the cam lobes for that cylinder are not rounded off. If they have lobes then follow livers advice. The cams are on top as in double overhead cams. A Yamaha engine.

A P0305 code can be due to a variety of issues that need further diagnosing and test equipment/scan tool to properly pin down the cause. Could also be a vacuum leak, faulty/clogged injector, clogged or dirty EGR issues, faulty cam or crank or TPS sensors, dirty MAF sensor, weak fuel pressure, low compression or valve issues, etc. Even some transmission shifting or converter clutch issues can cause a misfire code.

Clean the MAF sensor which might be due on your car with high miles… A dirty MAF can give faulty airflow signals to computer and cause a misfire. Parts stores sell special MAF cleaner spray… Just remove MAF and spray off any soot residue… Do not touch the sensor wire… Very delicate. You can also try checking/testing for vacuum leaks in hoses or that #5 cylinder area… Spray down the intake manifold sealing areas and TB sealing areas with carb spray with engine idling… If rpm's go up, that indicates a vacuum leak… Repair as needed. Clean the EGR valve and make sure it. Not sticking. You might also try swapping the injector for #5 cylinder with another cylinder and run the engine… See if the code comes back and stays at P0305 or switches to the cylinder that you swapped the injector to. If so, then injector is bad. If the code stays the same, then more testing is needed. If the code stays at P0305 perhaps do a fuel pressure test… And compression test and see if that cylinder is low… Possibly bad valve or rings issues.

Start with things you can do yourself and go from there if more testing is needed… Clean the MAF, change air/fuel filters if due, add some Techron in the fuel tank to clean injectors, check for vacuum leaks, swap injector and retest, compression test, fuel pressure test, etc. Many parts stores rent pressure testers so you can DIY… Specs found on websites or repair manuals.

"Common Problems That Trigger the P0305

Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable)
Incorrect ignition timing
Vacuum leak(s)
Low or weak fuel pressure
Improperly functioning EGR system
Defective Mass Air Flow Sensor
Defective Crankshaft and/or Camshaft Sensor
Defective Throttle Position Sensor
Mechanical engine problems (i.e.-low compression, leaking head gasket(s), or valve problems
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