New Member looking for misfire assist?

[007BlackTahoe]

I have 2007 Tahoe with a 5.3L and I’ve been banging my head against the wall trying to figure out a misfire at idle. I have searched the forum looking for answers (will try fuel pressure and rails next I guess). The misfire has been going on for about 4 months, seems to be slightly more noticeable when cold. Even more frustrating is the fact that there is no service code present, to guide me in some sort of direction. In attempts to isolate the problem, so far I have:

1) Cleaned the Air Cleaner
2) Cleaned the MAF Screen
3) Cleaned/sprayed the TB butterfly and throat
4) Replaced the Plugs (Bosch xxxxx)
5) Pushed original stock tune/program back into vehicle
6) Replaced the plug wires (Taylor 8.5MM)

Last time I had the oil changed, I had it hooked to a scan tool which showed cylinder 6 missing. After checking them, they indicated that all the plugs were loose (which I don’t necessarily believe, but economy is tough – so they torqued them and I paid). Drove for another month with no change, except for the bruising on my forehead from the continual beating against the wall. After another month, I had another shop hookup a scan tool again, which showed cylinder 7/8 missing. Reseated those wires at both ends (plug and coil pack) and still no change.

This problem just started over time and was not a result of any modification that I had introduced. All the attempts listed above were done after the misfire was noticed. The truck runs great, just the slight stumble at idle and there is no hesitation at acceleration. Has anyone experienced this issue or have any ideas what I can try next? This is absolutely driving me crazy. Was thinking maybe a Temp or O2 Sensor, vacuum leak, intake leak? Even had one guy tell me that although the plugs are speced out for my vehicle, should go with an OEM plug instead (but again, the miss was there before I changed the plugs out, so I discounted that theory). I just don’t know anymore and as I dive in further, it will get more costly. Bottom line, I’m trying to avoid just throwing money aimlessly at the problem. So I came to the forum for help!

I should note that my engine mods are the typical ones….a Vararam CAI, Magnaflow muffler, Diablo Programmer with custom tune and aftermarket plug wires – nothing crazy (unfortunately).

 

[Jounier11]

if u cant find the problem id suggest going to the dealer and pay them to have a look (if u don't wanna spend a lot of money xD )

 

[007BlackTahoe]

Well, "dealer" and "don't wanna spend a lot of money" really don't go together. But if anyone else is experiencing a misfire at idle, here is a synopsis to my next steps.

First, did a Seafoam induction service (fuel system and brake vacuum booster line, but not crankcase). No-Go, still stumbled on idle.

Did some research on the tahoe forum (and outside the forum) which point to several recommendations to replace intake gasket. Sounded like the right path, so I thought it might be foolish to replace the intake gasket, and not the intake itself...... as it is plastic and was also prone to cracks on some vehicles.

To add to the new found possible resolution to my idle problem, I stumbled across a smokin deal on a brand new intake "take off" with fuel runners, injectors, sensors, gaskets, complete assembly for $200 - NEW!!! Thought if it wasn't a bad gasket or cracked intake, I couldn't loose because it would also alleviate injectors, fuel rails, couple of vacuum hoses, etc.....

No-Go....same stumbling idle. I will say she runs noticeably better and is more responsive, but still stumbles at idle. Arrrrrrrrg. No CEL, just don't know where to go next???? Started to think fuel filter, but was told they run them on 07 Tahoes????