JFP in PA

Unless there is a TSB for the car recommending a TCU update, or the car was throwing codes, I would leave the TCU alone. Changing the control unit when it is not needed is just an added $500+ expense for no apparent reason. But get the fluid and filter changed ASAP.

On your car, the xenon low beam is a D1S, the high beam is a separate halogen H7 bulb.

If there is a single factor contributing to problems with the transmissions in these vehicles, it is the recommended service intervals. I'm sorry, but there is no transmission fluid made that will withstand 16 years of daily use. At one point, Porsche recommended 90K miles as the optimum interval; again way, way too long. Like most modern electronically controlled automatic gearboxes, the trans in your car has multiple solenoid valves and controls circuits that have incredibly small passageways. Over time, normal wear clutch dust, other debris, and even some varnish like materials will build up and clog these passageways, leading to everything from rough shifting to multiple fault codes, and eventually will cause the unit to drop into a kind of "limp mode". At that point, you are in for some major $ expenditures as the unit will at a minimum need a full service and a replacement valve body, or even a complete trans replacement (dealers are getting about $10K for that). Now comes the kicker: Normal servicing (a bit messy but doable DIY project) does not change all the fluid in the trans. A drain, filter swap, and refill only gets less than half the old fluid out. Because of the way the trans is designed, a large portion of the fluid is in the torque converter and cooler which does not gravity drain during a service (again, because of the design, pressure flushing of the entire system is not an easy task on the Porsche Tiptronic). So every time you service the unit, you are only replacing part of the fluid; and some very dirty old fluid remains and you are depending upon dilution with clean fresh fluid to help disperse any remaining crud, which is all the more reason to short the service intervals. We normally shorten the service intervals on Tip vehicles to no more than 40K miles for normal use, sooner for ones that tow or see more heavy usage. When I tell customer that, I usually get raised eyebrows or comments about the factory or dealer recommendations; and my response is that fluid is cheap, replacement valve bodies (just scan through the Cayenne section on any Porsche forum to see how often that subject comes up), or replacement transmissions, even used ones, ain't by any means cheap. If I were you, and as you have not mentioned any codes being thrown by the unit, I would ignore the dealer and get the trans at least serviced. You just might be surprised how well it may respond to a simple oil change.

Not really, as it only happens intermittently, it just feels a bit goofy.

If it is at or near lock when it occurs, yes. You have to remember, the car is never driven at any appreciable speed in that steering configuration, so it only occurs in a very narrow set of parameters and at very low speeds.

Normally, you can look up the exact trans model that is in the vehicle using the Cayenne's VIN number, which is what a dealer would do, but you can also get numbers off the trans itself.

The little 9V memory savers will work during a very brief (a few min.) main battery replacement, but are not designed to be for a longer term use. Several quality battery maintainers (Ctek comes to mind) have settings to hold the car's retained data for longer periods, but you have to work very carefully as many circuits will remain "hot" while this is hooked up. They also recommend against very long term connections.

Even if the problem goes deeper than Loren's post, a quick scan turned up used units starting at $1400 (flea bay).

I would strongly consider getting a new mechanic. All modern cars have upkeep cost, particularly if they have not been properly maintained. Porsche is no different than any other make in this respect. Get a Porsche shop to look at the trans, it may just need a service and possibly a valve body replacement, which is not going to cost $5k. We have seen more than one Porsche declared "DOA" by a shop not experienced with Porsches that was miraculously revived for a reasonable amount and happily back on the road for many more miles.

+1. A common complaint, and an easy fix.

I think this is the one you are looking for:

Sometimes, to get the most out of a suspension system under normal road usage, you need to make it a little cranky backing up at full lock.............. You would be surprised at some of the similar compromise's made on vehicles costing several times more than yours.

+1. This is one of the most common comments we get from first time owners.

If the plug tubes were leaking, there would be oil on the plugs as well as on the cam covers; if everything is dry, leave it alone.

As Loren noted above, you need to find a correct Bosch PCMCIA card in order to build one, and that will not be easy.

As noted in my post above, there are a lot of quality plugs and coils available; if you are unsure of what to buy, do what many owners do and stay with the factory choices for the components, which are proven to be long term performers. If your plug tubes are not leaking, leave them alone.

Porsche began to "see the light" on water cooled engines with some of their race engines which used air cooled blocks and water cooled heads. This carried over to the legendary 959 street car, which also used water cooled heads. The published rationale had to do with both performance and longevity, but the engineers noticed that emissions and noise levels dropped dramatically as well, which started the move towards all water cooled units.

That's it. Just out of curiosity, have you ever considered going to spin on filter?

There should not be anything between the engine case the bottom of the filter canister, which is where the bypass valve should be. I am not sure if Porsche still sells the bypass assembly separate from the canister housing anymore, but a good parts department should be able to answer that.

Yes, it is called "cam allocation", and covers several pages in service manuals, and requires some special tools as well. As Porsche stopped printing this information several model years before your car was built, you (or your technician) would need to obtain it from Porsche's online subscription service at http://www.renntech.org/forums/links/goto/18-porsche-piwis-tsi/

If you are referring to the fasteners that hold the VarioCam+ drive on the end of the cam, the answer is possibly yes.

If it was a loose gas cap, you would get a specific code of a large EVAP system leak.

I am not a fan of Mobil 1 products. Some of the Motul oils are pretty good, but if I were you I would be looking at Joe Gibbs DT40. I have never heard of internal moisture build up leading to misfires, but even slightly cracked coil packs will, particularly if it is raining or wet out. Moisture inside the engine is not a function of oil brand or type, it ususally stems from the engine not getting hot enough to burn it off from things like short trips.

If the fuel filter clogged, all the cylinders would begin to lean out and you would get an overly lean code from the O2 sensors, so I don't think it is necessarily that. You should also be able to see a clogged filter with a fuel pressure and delivery test. As I do not know what facilities you have at your disposal, I would suggest getting the car scanned on a Porsche specific diagnostic system (Durametric, PIWIS, PST II), looking for anything out of the ordinary (strange responses from the O2 sensors, fuel trims, etc.). As cylinders 1 & 4 look like a starting point, I would also pay close attention to them, pull the plugs and coil packs, closely checking them for any discoloration on the plugs, cracked ceramics, loose coil pack connectors, cracks in the coil packs themselves, etc.). While some parts may need to be replaced, I would not replace them without knowing why.

Most likely not; as you noted, it is a common occurrence on these vehicles. The most common misfire areas are spark (or lack there of) and fuel (overly lean/rich mixtures). Fuel issues tend to throw emissions codes, so I would start by checking the coil packs (common problem area) and plugs.