I know it's not a truck but it is a 4.6L Ford and this Forum has been a valuable sorce of info form my Bronco... so here it goes.

First the relevent installed aftermarket parts:
C&L Racer cold air intake system
BBK Twin 62mm TB
Diablosport Predator Tuner- C&L 91 octane tune installed

The "Event" rundown:
I've had the parts installed since late fall/early winter of last year and have had absolutely no problems what-so-ever. Then while driving sunday, not 5 minutes after I left the house the idiot light came on. There was no noticeable change in performance so I made the call to check it all out once I arrived at my destination. Once I got a chance to plug up the Predator to pull the codes (luckily I had it in the glovebox), the displayed codes were P0104, P0171 and P0174... all mean, you're running lean dummy! I stumped at first thinking maybe I had gotten at bad tank of gas or something, but then decided to check under the hood for s**ts and giggles to see if there was any other physical problems. Popped the hood and found that the hose clamps on the both ends of the intake tube had come loose and started to separate from the silicone house mounts allowing the system to flow a little more freely. Too freely... I found the source of the lean condition. Buttoned everything up, cleared the codes and ran into the store thinking problem solved. Came out, jumped in and started the car and bam! Engine failsafe mode. I pulled the codes again and this time got P1000 (OBDII monitor testing incomplete) and a bunch of codes (i forgot which ones specifically) referring to the throttle position sensor. I disconnected everything hooking up to the TB, made some adjustments, hooked it all back up, cleared the codes, and reinstalled the tune several times before I finally got the car to restart. Ran fine to my buddies house, no dummy light or anything else telling me there was still a problem. Left my buddies place about 5 hours later and the same thing happened. Redid everything I performed last time to get it to start and I was again off and running. Stopped and got a fresh tank of 93 octane @ BP, no problems starting back up and made it home without any more incidents. Went out to the garage yesterday to see if the engine would failsafe again and it didn't. But now when I turn the key to the ON position I hear electrical "pulsing"... kind of like a machine gun firing (speed wise) and it is audibley noticeable. The car ended up starting fine but I sure as s*** don't know what that noise is. It sounds very similar to when you get on a motorcycle after it's sat for a while, flip the kill switch to on, turn the key to on, and the battery clicks at you for a few seconds. So... anyone got any ideas??? Think maybe I F'd the TPS??? And what the hell is that noise???

Sorry for the length, but the more info given the less questions I'll have to answer in the long run. Thanks for the help!
Wayne

 

When you turn the key (not to start) all the gauges and lights come on without the clicking?

 

When I turn the key to the on position without actually starting the car I get the clicking noise.

After some more footwork of my own (since the guys on the mustang forum are blaming the AM throttle body on my problem instead of the air leaks), I think it's pretty safe to say that I'm going to have to replace the TP sensor. Forgot I had a slightly outdated service manual to reference. I really need to get out to the garage and do a little more diagnosing, had no chance to do so today.

 

Quick update: Ran out to the garage late last night when I took the dogs out and turned it on but didn't start it... the clicking is definitely coming from under the hood... where under the hood is for my next episode of Sherlock Holmes. It should also be noted that I the clicking continues even after I've turned the key to the off position. The duration of the clicking lasts for around 5 seconds total then stops.

 

Problem solved. The clicking noise was the TB butterfly rapidly opening and closing during the initial start-up test. I took the TB off the manifold, removed the TP sensor (which I believe was the issue) and the throttle plate motor and proceded to go through everything to make sure there was no binding or kinks in the system. Re-assembled everything, made some adjustments and turned the key to ON... no butterfly clicking anymore. Took the stang for a spin and all is well. Still decided to keep my order for TP sensor open just in case I did do some irreversible damage to it.

 

I guess it wasn't seeing the throttle blade in the correct position. I guess it may have been too far advanced and not seeing it close completely.

 

Yeah, I'm assuming that it just wigged out the computer and told the TB to go banana sandwhich. I'm just happy to be mobile again since the brakes are grinding on the Bronco.