As I come to a stop going about 35-45 or so my tach drops to 500 or so then bounces up to 750 or 800 then goes down to about 650. My tach is not broken, you can hear the engine as it does this.

I think this may having something to do with a possible miss I'm having. I'm not sure if the engine is missing or not when it's idling. It idles at 750 when in park and 650 when in drive. I recently had the PCV tube replaced becaused it was cracked. It was at the dealership getting fixed for something else allready. Anyways the CEL wasn't on, but they hooked it up and got the infamous P0171 code. They replaced the tube and cleared the code, drove it, and said it was fixed. I couldn't tell any difference. The idle seems a bit rough, but it's not very noticeable. I've read that the 5.4 has a bit of a rough idle anyway.

I appreciate any input.

 

Anybody? Please.

 

Sounds like another vacuum leak. Check everything that the dealership did.

 

After doing alot searching, I was thinking more along the lines of cleaning the MAF and the throttle body/IAC. Especially the MAF. I have a K&N. Alot of people have had trouble with the oil getting on the wire of MAF and causing problems. I would think a vaccum leak would cause problems all the time. This just happens when I let off the gas and come to a stop. Then again there are alot of vaccum leaks associated with this error. Then again alot of people struggle forever and never fix this. I should probably stop by Autozone and get it scanned for codes.

 

Could be. I was just giving an idea of something that is easily(sometimes) diagnosed. Vacuum leaks are horrible. They can cause any number of problems and they're kinda tricky to pin down sometimes.