2002 F150 FX4 about 82000 miles anyways has a rough idle. Your can physically feel the truck shake about every 3 seconds pretty bad in the cab other than that it vibrates.

Took it to dealer said there computer in Mode 6 detected a random misfire on several cylinders at idle under load the truck does fine.

Have changed spark plugs Also new boots PCV valve Idle air control valve with a Duralast from Autozone. Throttle posistion sensor from O reillys Borg Warner. also took it in and got a motor vac done on it Power flusing the fuel system and De carbon it. No change. It used to crank up just fine now along with that rough idle It was a hell of a time starting when cold Almost acts like someone has there foot halfway down on the gas when starting it. Hard cold start I dont know where to go from here has also been tested on a smoke machine for vacuum leakes none to speak on.

Has good fuel pressure as well tested that. I dont know why it idles like this and has a hard cold start Im at Wits end. I like my truck but its hard for me to since my Chevys have never ever done this.

Help Please!!!

Also idle seems to be fine when cold sometimes it will jump a little but it really doesnt get nasty until it warms up it doesnt have to warm up much for it to start the rough idle either.

 

check your compression sounds like you may have blown a head gasket to me my truck did the same thing and after putting to much money in it i finally found out it had blown the gasket in between two cylinders due to a plugged converter i would have never thought of a head gasket because it wasnt mixing my oil and coolant i finally traded the truck yesterday (97 f150) for a 2003 honda civic i hope this helps and hopefully your head gasket isnt gone its a big and costly repair it was to much for me to justify putting in to my truck good luck and all the best

 

Well i have so far not had a sign of that no exhaust smell low coolant etc.. So i dont know but this is getting pretty ridiculous.

 

crankshaft or camshaft position sensor... those two sensors tell the injectors when to spray and tell the spark plugs when to fire (they measure the position of the pistons and cam lobes), so if either is bad then that'll easily cause a misfire.

 

neither did i that is why it was such a big surprise to me when it happened

 

Came back from the Mechanic he tested everything you gueys said and more almost everything says sensors crank sensor everything tested just fine. He has no idea what is causing this rough idle.

However he said the computer showing its really not a misfire but more of an rpm fluxuation that jumps around randomly on the cylinders. So no idea what is causing this its completely annoying all i know is when its cold it runs a little rough but a hell of a lot better than when it warms up and the rpms drop to normal.

 

idle air control valve.. clean the MAF

 

Cleaned the Maf has a new IAC. however its a duralast From Autozone lol.

Forgot to Mention The truck also sometimes hesitates when taking off it will take off fine then it seems like there is a bit of a dead spot in the Gas peddle Then its fine only does it once in awhile Throttle posistion sensor has been changed.

I know its a tough one trust me...