First off, let me preface this post by stating that I am not a Jag tech, justa guy that has a moderate propensity and affility for cars and car-related stuff as a hobby.... alright, more of an obsession but who's keeping score anyway ! That means you should take thisinfo in the non-professioinal helpful spirit in which it's intendedand if in doubt, check with yourdealer. (There, that should keep my attorney happy.) Anyhoo,Irecently got anengine error code indicating"restricted performance" during a moment of "spirited" driving between exit ramps on the highway. This was discussed in the thread: "XJR Restricted Performance" https://www.jaguarforums.com/m_9428/tm.htm. However, my subsequent findingsprompted me to add this current thread which details some info I found out andelaborates on information posted by Envy337 in another thread which is relevant to all Jaguar owners with AJ26 V8 engines.

It seems that my error code was related to a not-so-uncommon problem in Jaguar AJ26 V8 engines. The problem is the throttle body bore and throttle body blade can become coated with a soft sticky carbon deposit over time causing driveability issues which sometimes prompt engine error codes resulting inthecomputer management system todefault to a"limp home" or"failsafe" mode. This causesdecreased (restricted) engine performance until the problem is found and corrected. In my case itseemed to havebeen no more thanthe throttle body and throttle blade needing a bit of a cleaning. Jaguar has issued service bulletins to address theseBulletin 600-03)Part-Load Engine Breather -Partial Blockage of Restrictor - Scheduled Cleaning - Service action S474, and (Bulletin 310-06)Carbon Deposits on Throttle Blade - Cleaning Procedure (amended 2/02).

The engine breather should be cleaned every 10K miles to reduce the contribution of the carbon buildup problem in the throttle body. The throttlebody should also be cleaned every 10K miles to keep the throttle blade and throat carbon-free and able to operate freely. Be sure to keepyourair filter renewed or cleaned (if you have a K&N "permanent" filter)periodically, as well.

Here's what I did. (You should disconnect the battery for some reason first, so remove the negative terminal. BTW, the battery is in the trunk, or boot ) I removed the plastic intake tube between the filter box and throttle body (two hex-head screws need to be removed). The oil breather tube can be removed by squeezing the collar (just like on apill bottle) and twisting alittlewhilstpulling up. There was very little carbon buildup in my throttle body,but I figured what the hey - clean it anyway. I took my carb cleaner spray and sprayed a rag to wipe as much off as it could, renewing the rag and keeping fresh carb cleaner on it. I held the "butterfly" throttle blade open and got down inside the walls of the throat and the edges of the blade. With most of the "heavy" buildup off (which wasnt much anyway) I sprayed the walls of the throat and theblade. It looked like new . (BTW,the car wont run with the intake pipeoff (because of the airflow meter), so if you try to start the car with it off and it dies, dont be alarmed.) I put everything back together and waited a while.Went outand it started right up (big plume of lovely smoke out the tailpipes!) Drove it around a little to get up to operating temp, then took it on the highway and nailed it! (several times) No engine malfuntion light came on and no error codes. Woohoo![sm=yeahsmile.gif] This means no 3 hour trip to Tampa and back for service (this time...)

Even if you dont have an error message or engine light (yet) you might consider doing this as a matter of maintenance - especially if you dont have your car serviced by Jaguar. (they are supposed to do it as a matter of routine at service intervals but not everyone goes to the dealer for scheduled service). Good luck and happy motoring!

-Kent