My truck is an 07 FX4 5.4 Supercrew.I recently had my plugs replaced by a reputable independent garage. During that fiasco, one of the plugs broke off and ended up on top of a piston. It cost me over $1K to get it fixed (head removed, etc). Needless to say I was less than pleased but what can you do?

Ever since I got the truck back (1000 miles ago) it has had a hesitation on taking off that has gotten worse. It went from a hesitation to a intermittent serious "dieseling" when you drop to idle speed like pulling into a parking place or drive thru window. It absolutely sounds like it's going to kick out a rod! It runs and sounds great any time it is not at idle. The 1st time it did it, I shut the engine off immediately and let it set for several seconds. It started right back up with no issue but has continued to do this and seems to be getting worse. I finally got a diagnostic code/check engine light. I had a buddy plug his code machine in and cancel the light. The code is P2004-Intake Manifold Control stuck open Bank 1. It happened the 1st time and I went back to the aforementioned garage to make an appointment to bring it in. It has since clicked on the check engine light the 2nd time. I dropped it off there this morning with the light still on.

My question; is this possibly a result of something the garage did while my engine was torn down or just some sick coincidence? What might this be and what will possibly be involved in resolving it?

Thanks.

I bought the truck with 69K miles on it and it has already cost me wayyyy more $$ than my 01 F-150 5.4 did on maintenance costs in the 10 years I owned it.

 

Any other codes?

 

None, Same code both times.