In Park, in driveway; engine cold and warm...it has a rough idle and sounds like it wants to stall.

In Drive at stoplights, same as above.

In Park, in Driveway, engine warm or cold, at about 3000 rpm it starts to flutter and won't tach higher than about 3100.

I just replaced the fuel filter (with help from the forum!) and it didn't change anything.

I pulled the cover off the air filter and tried revving it up w/o the air filter in the way and it still did the same thing about 3000rpm.

Recently had the gas cap replaced as it was throwing that code.

ATM, I'm just borrowing this truck but thinking about buying it.

I'm thinking maybe EGR, or MAF or?????

thanks for any help you can give me!

 

Computer has Rev Limiter when transmission is in Park or Neutral, so 3,000-3,500rpm would be top RPM, that is normal.

After engine is warmed up, idle should be 750-800rpm, unplug the IAC(idle air control) Valve engine idle should drop down to 500rpms or stall, either is fine.
If idle doesn't drop you have a vacuum leak or IAC valve is stuck.

4.0l's eat spark plugs, change them if you don't know when they were last changed, use Motorcraft or Autolite spark plugs.
'04 4.0l SOHC engine uses longer plugs than 4.0l OHV so make sure you get the right spark plugs

 

ah, kk. thanks on the in-park rev limiter.

will check on the rest.

Thanks!

 

Could be the MAF or the TPS ( throttle position sensor )

 

time to run some seafoam through the engine`s fuel injectors

 

I've got a bottle of Lucas to run through on the next fill up.

I'll check all the rest of the suggestions!

Thanks!