I took the truck out today (02 f150 4.2 v-6) check engine light came flashing on with a very very rough idle. I got the codes read by Auto Zone and my brother figured out it was a bad coil (he's a Mechanic for Chevy)

replaced coil pack today-- that cleared that check engine light.

replaced spark plugs, wires, fuel filter as well today just becuase it has never been changed now with 78K on it.

the problem now is that no codes are showing up now and at idle the truck sometimes wants to stall, but never does. what could cause this sudden urge to stall with all these new parts now?

(dealership is no option to us)

 

your gettin close to o2 sensor mileage

 

Fuel trims? BARO? What are the O2s doing when it starts choking out? You've already thrown some parts at it, we need more information so we can fix it this time.

 

what I know is that when you let the truck idle, it can be idling just fine, then all of a sudden it bogs down like its going to stall but does not. If you step on the gas just a hair and make the RPM's rise little bit, it idles fine, but does not idle right at normal idle operation. Check engine light does not come on anymore after replacing coil pack, new plugs, wires and fuel filter and the light contiunes to stay off even after the engines bogs down.

 

Was it doing this before the new parts were installed? If not, it could be possible that you've knocked a vacuum line off....it does take much of a vacuum leak to make these engines act really funny.

Sidewinder

 

yes, it was ten times worse before replacing the coil pack. Now that we have new parts in it, we were thinking it has bad gas (last fill up was at a BP station and it wouldn't be the frist time we have had bad gas from them)

He got some fuel injector cleaner and a bottle of dry gas and poured it into the gas tank. So far it "seems" like it calming the engine down, but I won't be positive until it runs that tank of gas through the engine.

I'll take a look at the vacume lines though to make sure there all snug.

 

Clean or replace the Idle Air Control Valve (IAC)

 

+1 for IAC