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Discussion Starter #1 (Edited)
I have noticed that my 2008 H6 Tribeca is hunting and surging at all RPMs, I can feel it at cruising speeds, and notice it at stoplights too. The variance never gets low enough that the engine stalls out or shuts down. Additionally, I have no lights on the dashboard at the moment.

I do believe I have worn out Cats, because of the P0420 that I've had in the past, but repairing a hole in the muffler seems to have helped that a little bit and that code is only intermittent now. Vehicle has 133k miles.

Any troubleshooting procedures you can think of? I poured a can of Lucas Injector cleaner into the tank today as a starting point.
 

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I'm thinking you may have a vacuum leak and I doubt the cats are the cause of that code. There are a ton of things that set off that code from gas quality to plugs to vacuum leaks and exhaust leaks and on and on. Mine was cleaning the grounds that fixed that code.
 

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Wow, thanks for the knowledge. I have never tackled a vacuum leak before? Is it as easy as ordering vacuum line and replacing the one that's there? Any interference parts that I need to get access to? I'd love to see a guide.

Also is there a test I can do for this, or is this just a replace and see if the problem went away?

To clarify, it sounds like you believe the vacuum leak might be causing both my rpm and my P0420 code.
 

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Wow, thanks for the knowledge. I have never tackled a vacuum leak before? Is it as easy as ordering vacuum line and replacing the one that's there? Any interference parts that I need to get access to? I'd love to see a guide.

Also is there a test I can do for this, or is this just a replace and see if the problem went away?

To clarify, it sounds like you believe the vacuum leak might be causing both my rpm and my P0420 code.
 

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I understand smoke testing works well for vacuum leaks, but have no personal experience. Used to be you sprayed wd40 around places that could leak air and listen for a change of rpm. You might check that all the bolts are tight that mount the manifold to the head as well as the throttle body to manifold. Inspect all the hoses for obvious damage etc.
A vacuum leak can cause that code and it can cause running problems too. I'm not saying that is your problem, but it should be investigated.
 

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I've been thinking and the first thing I would do is clean and shine all the ground connections. Remove both cables from the battery and shine up the terminals and posts. Then do the ground cable at the other end on the engine as well as the aux ground by the relay fuse box. If there is any corrosion on the cables it would be good to replace them. This won't cost you anything unless a cable needs replacing and would eliminate one source of trouble.
 

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Discussion Starter #7
I've been thinking and the first thing I would do is clean and shine all the ground connections. Remove both cables from the battery and shine up the terminals and posts. t.
So your saying that a poor ground may cause a rough idle? Or is this just to maybe help the p0420?
 

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Discussion Starter #9
Surging SOLVED!

My initial line of thinking was sound. My car was reving high, then low, then high, then low etc. I had a code (P0420) Emissions Related (O2 sensor below threshlod). Because I had nothing else to go on, I believed the two to be connected.... They were not.... When my idle and surging was happening my AC also stopped working. I believed this to be because the RPM was so low, that the compressor just couldnt do its job, all while the ambient air was 100 degress, making me feel like i had no cooling. So I looked down the engine route. Air, Fuel, Spark.


It took a friend to switch my thinking on its head. Maybe the A/C was the info I needed, not the error code. I waited for the car to do its symptom, and turned the A/C off. The car idled perfectly as designed. SO now i knew I had an A/C issue. It was the A/C cycling on and off repeatedly, that was changing my RPM up and down. I proved that by listening to the compressor clutch click on and off on and off.

Luckily the A/C was fixed in the easiest possible way, on step one. Hook a guage to it, and see if my pressures were correct. they were not. System was overchaged.

TLDR: in the hottest of days my A/C was overpressurized kicking the compressor off and on off which in turned changed my RPM making it appear that it was surging.

Now all I need to do is get rid of P0420....
 
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