I haven't been able to find a list of common issues to 24v VR6 motors so I will go ahead and start one. (Just as a note, most of the problems are minor, 24V VR6s are reliable motors)
Coilpacks - Can go bad leaving you stranded. Not as common at 1.8T coils. MIL light flashes and throttle is turned off. Causes misfires and many misfire codes. Causes stalling and rough idle. Several versions have been made. Version A-D are very failure prone! Stay away. Other revisions: D G J K N *update*: Old part number revision N #022-905-100N NEW PART #022 905 715C
You can check coilpack by unpluging while engine is idling. If that particular coil does NOT change the idle when unplugged, that coil is bad.
Intake shifter rod/bushings - The variable stage intake manifold's bushings wear out causing idle issues and noise. May sound like loose marbles in the intake. A company makes beefier aftermarket bushing to prevent it from happening again. Company: Gruven Parts (Vortex doesn't allow direct links) dot com
Warm Stall - covered to death in other threads. Suffice to say it sounds exactly like its name and a reflash from the dealer can fix it. Engine revs when you start it, then dies. Here is the TSB if your dealer wants to know: TSB 01-04-04 Free fix if you are still under warranty. (FYI, if you are chipped, taking it to the dealer for the software update will ERASE your chip! You can get updated code from your chip manufacturer for free to fix warmstall afflicted chipped cars) http://forums.vwvortex.com/zerothread?id=1297652
G62 Coolant sensor - If you have a black sensor, it WILL fail as all MkIV motors. Symptoms is a CEL and/or gauge fluctuation.. New version is green. I picked up the new green version plus o-ring at the VW dealer for $3.42, but it seems now the price has gone up to $20. Many have reported a drastic drop in gas mileage when the sensor went bad. VAG part#059919501A Location and install: http://forums.vwvortex.com/zerothread?id=3386797
Timing Chain - *NOTE* This is only an issue if you hear noise. There are NOT many reports of failed guides on 24Vs. Higher mileage motors might have the chain tensioner or the guide rails fail. Doesn't happen anywhere near as often as the 12V VR6s as they changed the guide rail designs quite a bit. Result is bent valves, damaged heads, and a really big paperweight. Best to change as soon as it makes any strange noise (noise from the driver's side of the engine is an indicator, slight chain noise is perfectly normal, remember there are 24 valves in there). Requires removal of tranny and engine from car.
Stretched Timing Chain - Common in Eurovans and Forced Induction engines. High heat and high loads can cause the timing chain to stretch, resulting in a mistimed engine. Using conventional oil or abusing oil change intervals is the usual cause of stretched chains. Will cause a CEL for cam/correlation errors.
Water pump - fail as the impellers are made of plastic, but more commonly the seal & bearings fail. Can break apart and clog cooling system causing cooling system inefficiency/problems. If it starts to make noise, change now! Metal impeller model is available but can be hard to find (Hepu brand). Recommended interval for changing is 80-100K depending on who you talk to. But many fail earlier and may fail as early as 20k. Change as preventive maintenance.
Auxiliary (Secondary) After-run coolant pump - The secondary water pump runs for 10 minutes after the ignition is turned off. Usually only fails on high-mileage motors. You will hear a soft "whir" from the front end. Symptoms of a failed or failing pump is no noise, very very weak noise, or pulsing. This is due to the sealed design of the electric motor, all the brushes' dust stays in the motor gumming it up. It can be repaired by taking the motor apart and cleaning in or by simply buying a new pump for around $100. It may seem like it doesn't do much, but VW is notorious for cost cutting, so why would they add a second water pump unless it did something important? It keeps the aluminum head and block cooling at the same rate to avoid warpage. VAG part# 3D0 965 561 D
Thermostat housing/coolant flange & "crack pipe" is plastic and can break and leak because of heatcycling. Best to replace with waterpump. Several companies sell metal water distribution pipes aka "crack pipes" if you want to upgrade.
CELs in general. Primarily Catalyst below efficiency threshold and oxygen sensor related codes. Most likely causes are bad MAF, bad oxygen sensors, or poor quality gasoline. Can be caused by failing converter, but is much more likely to be the previously stated reasons.
Pinging - These cars ping. Only use 91 octane to prevent most pinging. It is annoying but you have to get used to it. Sorry.
MAF sensor - Frequently go bad as with all MkIV motors. Clean often to avoid CELs. Most automotive stores sell MAF cleaner now, but electronics cleaner works just as well. The VR6 MAF sensor is the same guts as the 2.0 sensor but the housing is bigger. You can easily remove it from the new housing and mount in the old. Buy what is cheaper. (I hear now they changed the parts so now they are the same part # and come without the housing, you must reuse the old housing. Can someone else confirm?) EPC, Check Engine, & Stability Control light will illuminate when MAF codes are thrown. Also, can cause poor idle and general running problems. Unplug sensor and see if idle improves. If it does, sensor is bad.
Dual Mass Flywheels - once broken or messed up, they stay that way. They are very expensive to replace and CANNOT be resurfaced.
Oxygen sensors - they fail often but with most modern cars, they should be replaced at regular intervals. Can cause CELs. No rule of thumb has been established for replacement, but changing with sparks plug on other cars is a guideline, but I *think* they should go 60k before replacement. Shop carefully on these, many dealer will charge $200 per sensor; you can get these cheaper elsewhere.
Serpentine Belt Tensioner Pulley Bearing may start to squeal. You can save it if you act before it get worse. Repacking the bearing with grease can save the bearing and extend its life. Otherwise, you must buy a new pulley. DIY for a 12V but procedure is identical: http://forums.vwvortex.com/zerothread?id=1138497 - 12Vs use a 7 rib belt, 24V use a 6 rib belt (24V specific). Be careful when ordering belts and pulleys! *update* Gruvenparts now offers the 24V VR6 Idler pulley (6 rib) with beefier and replaceable bearings.
Fan Fuses - The fuses for the cooling fan may pop, causing overheating and no a/c. If it continually pops, it is most likely the fans have gone bad shorting internally. Vary rarely, the fan control module or temp. sensor may be faulty. See this thread: http://forums.vwvortex.com/zerothread?id=3126433
The cooling fan's low speed die caused by bad resistors in the fan motors (which is probably why the above fuses pop). You can just replace the fans or fix the design flaw by either adding external resistors, adding a PWM controller (new VWs have PWM controlled fans), or outright bypassing the FCM (fan controller module). Fan low speed remedy and why it happens: http://forums.vwvortex.com/zerothread?id=3890491
More low speed info (see bottom post): http://forums.vwvortex.com/zerothread?id=3844295
FCM Bypass: http://forums.vwvortex.com/showthrea...zable-solution.
Just a heads up - the throttle valve needs to be cleaned to prevent idle problems. Every 40K should take car of it. Simple procedure (for 12V but very similar) http://forums.vwvortex.com/zerothread?id=1116399
So what did I forget? Lets build the list up! Part # and link would be helpful too.
Engine related but more general MkIV problem: Fuel pump relay: may fail resulting in no fuel to engine. http://forums.vwvortex.com/zerothread?id=4076745
Also a major problem: Transmission related: 02M slave cylinder in tranny fails requiring removal of tranny to fix, for a $60 part. Usually happens around 80k-110k miles.