I have two problems first I have a 99 f150 4x4 with a K&N generation II air filter it makes the truck stumble on take off, and second a intermittent whistling noise coming from behind the throttle body near the fire wall. Any ideas.

 

Welcome to the forum

Both problems are probably from a cracked PCV hose elbow at the rear of the intake manifold. This is quite common. You might also spray the MAF filaments with contact cleaner just ot make sure no filter oil has gotten on them, just don't touch them, they break easily.

 

Thanks for the info. Ford checked me out in the parking lot and said it was my K&N filter and some valve at a cost of $260.00 parts & labor. I'll check it out. Thanks again

 

The K&N type filters work better when you do a battery disconnect or PCM fuse removal to allow for the computer to "relearn" it's behavior.

-Kerry

 

That one didnt work, but thanks anyway

 

Clean the MAF and the IAC.