Dealer service rep says the fluctuating idle problems I'm having with 09 SC XF is being caused by a bad cat... I'm not a car mech (helicopters, but with no cats on them), but for the life of me, I cant see how this is causing a 500 rpm fluctuation at idle. Could a blockage in the cat cause this? It only has 52K miles on it... Not wanting to drop the almost 2K the dealer in this country is certainly going to charge for the part if he's wrong...

 

Ish, I would start with cleaning the throttlebody first and making sure to get the idle air control valve port nice and clean and then see what you have at that point. Get yourself a can of "throttlebody cleaner" (not carb cleaner). Remove the intake and get access to the butterlfy valve that is there. Then, using one hand, hold the butterfly valve open and with the other, spray away all the brown gunk that is inside the throttlebody. Make sure to get the butterfly valve (especially the thin edges that can come close to the outside bore of the throttlebody). Reassemble everything and then start the car. Of note, you may find that the car will not want to start after doing this depending on how much throttlebody cleaner you used. Do not worry. Depress the gas pedal fully, start the car and once the RPMs start to come up, release the gas pedal, apply it as needed to keep the motor running. After a few seconds the motor will even out.

See what you have at that point. i bet you will find that your idle issue is gone.

 

Its at the dealer right now, and I specifically requested that the throttle body be cleaned because of the info found on this site. Customer service in this cats litter box of a country is so freakin' bad, I doubt it was done like I asked.

 

Ish, get it back from them and do it yourself. If you have even a little bit of mechanical ability, you can clean the throttlebody. it isn't hard. The biggest problem you may have is getting the hose off the front of the throttlebody. Worst case, take a picture of the clamp, post it here and I can step you through how to pull it apart and put it back together. Then all you are doing is if you see brown, you spray it with the throttlebody cleaner. Keep spraying till everything is a nice silver. The only "trick" is finding a little hole (normally at the bottom of the throttlebody) and squirting some throttlebody cleaner down the hole (this is where the air goes for the fine tuning of the idle).