When my truck idles in park or nuetral the exhaust "hiccups" everyonce in awhile maybe like 2-3 times in a minute.. when it hiccups it sucks in air from the exhaust pipe.. like ill stick a dollar right behind the pipe and when it hiccups its sucks the dollar inward instead of blowing it outward..

Heres what makes it odd though.. if i put it in gear it idles perfect.. smooth clean i mean just perfect.. but as soon as its in park or nuetral i starts poping and he hiccups again..

Oh and I have the 4.9 300I6

 

Was introduced to the dollar bill trick a half century ago, haven't seen or done it in years. Don't think you have a valve problem but a compression check would verify. Is this a carb or EFI? Am thinking a minor mixture problem and when a load is on the engine its just masked. Being at idle don't over look a vaccuum leak.

 

Yeah my dad showed me the dollar thing.. its EFI.. and ive tried checking for vacuum leaks.. but i cant hear any and ive tried spraying starter fluid around all my hoses but never heard any increase in RPMs..

 

Any one else have any comments on this?

I dont think its actually doing any harm to the truck.. but its extremly annoying to me

 

I just went and pulled the codes.. this was engine off test..

the codes came up like this..

67, 81, 67, 81, then a single flash, then 18, 32, 18, 32

 

67-Park/Neutral Position (PNP) switch circuit open - A/C on during Self-Test
81-Secondary -Air Injection Diverter (AIRD) solenoid circuit failure.
18-SPOUT circuit open. orIDM circuit failure/ SPOUT circuit grounded. or ignition diagnostic monitor (IDM) circuit failure
32- EVP voltage below closed limit.

hope this helps

 

The Park nuetral thing might be because of the way my truck is wired with a push button..

As for the rest of it.. i really have no idea what it is or means lol

 

Ya I couldent tell you what half of this crap means, but maby look in to 18, and if it is a sensor then replace it sensors are cheap