360 Cat failure?

The cat ecu is pretty notorious for failing so I would start there. It causes the slow down even when the cat isn't overheated; It can throw a slow down shortly after startup too. Did you use a temp gun on the cat? If so what temp was it?

 

buy a temp measurement gun (very cheap these days) and shoot the cat next time it happens. Usually if it's bad it'd be glowing red. As noted above the ECU's that measure the temp as simple and fail. They're easy to get to and exchange, but confirm issue before you do anything. 200 cell cats will work fine, however you may end up with 0420/0421 error codes suggesting your cats aren't effectively filtering...

 

And no, no concern that the cat is 17 years old.

 

buy a new cat ecu and replacing it with a new one(15 min job) is less expensive than a dealer diagnostic I believe?

 

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Sorry for the interruption, Fernando. I simply could not resist sharing my all time favorite "cat failure".

 

Sorry Fernando about your cat. Not sure why they self destruct like that.

 

Pretty sure cats are a service item in the manual. Will check when the are "supposed" to be replaced. But as above ^^^ an old cat may not be at it's best.

 

It can also be the thermocoupler's associated with the ecu's. Replace them all and the problem should stop or wait till it show's "slow down" again. Mine was showing slow down at start up so I knew it wasn't the cats.

 

yes.
there's also an el cheapo audi cat temp ecu that you can use, but u need to splice harness

 

Possible but this is rarely the problem. Start with the simple stuff. Thermocouples are basically bimetal contacts in a sheath so not much to fail there.

 

Most likely the cat ECUs but get a $35 infrared thermometer to be sure the cats are not actually overheating.


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This particular cel is one of many 360 issues that can be diy for low $.... or can be farmed out for big $$$$$.

Amazing spread between new oem bits and serviceable used or am items.

 

Thermocouples are easily checked with a multi meter. Just set to continuity or resistance check, if the two pins don't measure close to zero ohms or continuity it's failed. They are a very simple device. Cat ECU info available at www.technistrada.com

 

Correct! Also check from the leads to the case, that should be an open.