RPM's bottoming out... Can someone help!
 

I seem to be having a slight issue with my 05 FX4 Screw 5.4L. At startup the engine rpms jump up real high (around 1500) and gradually come down. This seems to be kinda normal for these trucks. But lately after it comes back down to that normal range of about 550-730, the rpm's just go lower. When the truck is in park or drive and it is stopped the rpm's bottom out around 340 or so and when I am going from reverse into drive the rpm's get so low the truck stalls out. I recently purchased a Evo to watch some numbers and change the stock tune over to the towing or performance tune and have noticed the erratic rpm's and I have also noticed that the spark advance is extremely low sometimes going to around 4 even in drive. I would think that normal operating numbers should be in the upper 20's and low to mid 30's. Is this a problem with plugs? I have 89,900 on the odometer and I bought the truck used, so I have no clue if the plugs have been changed.... Can anyone here give me some idea's on what this is and what I might need to be changing.... also any idea's on what maintainence I should do not knowing its previous history?

I'd start by cleaning the MAF and TB... see if that helps

And change the fuel filter... who knows when the last guy did it. Its a cheap fix.

mine did the same thing and IT was the plugs for the most part. I bought mine new and put 180,000 miles on it before changing plugs. I will tell you that you need to go purchase the ford 3v spark plug remover from somewhere. You can purchase it online or at a parts store. It is imperative that you do this! The carbon builds up around the end of the plug and it breaks off and stays in the head past the threads... NOT GOOD! Also the spark plugs are a pretty penny themselves, so be prepared to do this on a weekend or when you have the time to do it.