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Discussion Starter #1
Sorry if this has been covered before, but my issue is not misfiring I dont believe. Couldn't find anything on my problem, so here goes:

My 2006 Touring (160k) has had the valve adjustment done, new plugs, repaired leaking tube seal, new downstream O2 sensors.

About 6 months ago it started "skipping" when stopped at lights or in drive-thrus. No CEL or codes, so I figured it might be injectors dirty so I ran cleaner through it. More recently I found out my wife was putting reg octane fuel in (since we've had it 2 years). I had her start using high octane as called for. Additionally, I've noticed ithe skipping was not as bad, but noted one common factor: only skips in gear, when the AC is on. It is intermittent and sporadic, but always when AC is on, foot on brake, in gear. I noticed the engine actually shakes when it does it as well. It feels like someone bumped your back bumper with their car.

Half way through first tank of high octane gas, CEL comes on for cats (both showing bad). Both cats are coding in the CEL needing replacements, which I find hard to believe. I ran catacleaner through per instructions but CEL is still on.

My question is are there any thoughts on the skipping? I don't think it's related to the cats, but I may be wrong. Not sure what else to try, unless I start replacing coils one by one.

Thanks and be safe.

'
 

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My 05 with 196k does that every now again in the exact same conditions you see. It started last summer. I run premium all the time, so for me I don't think it is a fuel octane issue. I've not thrown a CEL yet (knock on wood). I haven't figured out what causes it and until I get a CEL I don't know where to start.

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Could be a lot of things - partially due to the extra load as your AC compressor cycles on and off. Anything that's really marginal might cause a misfire, which will dump unburnt gas into your cats. For this to be the problem, there would have to be a common problem between the two banks, as each has their own cat.

Or, it could be the surge in idle speed being just enough to "engage" your torque converter (doesn't usually happen). What's the service history on your transmission?

On regular gas - I really doubt that has anything to do with anything. I used regular on my many long (!) road trips and could see virtually no difference in interstate-style cruising. I did run premium around town, and in the mountains though "just because".

Have you ever replaced the upstream O2 sensors? They would be more likely to cause problems, though (it seems) both would have to fail to cause a problem with both cats.
 

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Discussion Starter #4
Yes actually replaced upstream front O2. Previous owner had 100k service done before we purchased it (timing, etc.). The skipping has become frequent again so I may start replacing small components and see what happens. Not sure what else I can do at this point.
 

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Could be a lot of things - partially due to the extra load as your AC compressor cycles on and off. Anything that's really marginal might cause a misfire, which will dump unburnt gas into your cats. For this to be the problem, there would have to be a common problem between the two banks, as each has their own cat.

Or, it could be the surge in idle speed being just enough to "engage" your torque converter (doesn't usually happen). What's the service history on your transmission?

On regular gas - I really doubt that has anything to do with anything. I used regular on my many long (!) road trips and could see virtually no difference in interstate-style cruising. I did run premium around town, and in the mountains though "just because".

Have you ever replaced the upstream O2 sensors? They would be more likely to cause problems, though (it seems) both would have to fail to cause a problem with both cats.
+1
 

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Check for vacuum leaks, and you might try pulling and cleaning (or replacing - they're dirt cheap) PCV valve. Also, the throttle bodies get pretty grungy, and can affect the idle. There are a host of other sensors and widgets that could be contributing to your problem. I don't know if hooking up a laptop running the HDS would show anything, but it might help.
 

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Discussion Starter #7
Replaced PCV this year and cleaned up throttle body late last year. Will def check for vacuum leaks though. Haven't done that
 

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After cleaning the throttle body, did you reset the TPS?

OBD2 data from a scan tool or HDS might help narrow down the issue (e.g. fuel trims could help identify which bank misbehaving, MAP pressure could show a vacuum leak, throttle position could indicate the need for TPS reset)
 

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Discussion Starter #9
No I never reset the TPS. No codes showing other than cats but I guess a better than usual scan could be beneficial
 
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