Why would a 00 VW GTI not idle?

More than likely heater core leak, I assume you are losing coolant. I've changed a couple heater core in my life but nothing like changing the one in the video. I saw 3 videos, and all said you have to pull the dash.

How VW Parts Fail ~ Heater Cores - YouTube

VW Heater Core Replacement - 1993-1998 VW Jetta and Golf - YouTube

Hi. Please check the spark plugs, if worn this can happen. Also if the injectors are leaking into the cylinders. This i have seen only once in many years on the 2003 GTI.

Hi. Is this a vr6 or a gti? they have different engines.

What faults codes are showing on a test of the electronic engine control module?

Have it checked at your local garage. White smoke from the exhaust system.....normally means a cracked cylinder head gasket. I would check the oil dipstick to ensure that there is no coolant in the oil pan. Coolant in the oil pan could mean a cracked cylinder head......a more costly repair.

Did you resolve this?
I drive a mk3 golf GTI 8V and mine starts fine but after driving for about 3 minutes (engine warms up) it starts to misfire, the car stalls and then you can't start it again until the engine has cooled. Does this sound similar?

This engine requires synthetic oil, 5 quarts, and oil filter. Remove dip stick, remove oil drain plug at bottom of engine oil pan, remove filter housing, remove oilf filter and o-ring. Replace o-ring and filter, rub o-ring with some new oil, replace filter housing, replace oil drain plug, pour new oil in at top of engine oil cap, replace dip stick, start engine, run for 45 seconds, turn off, check dip stick to make sure oil is at correct level. You are done, recycle old oil.

What do you mean? In the fuel line? In the manifold? In the tank? In the engine/cylinders? Do you want to measure A/F mixture? I am guessing you are asking because your car wont start. I am also guessing it cranks and sputters to try to fire, but never catches and runs. Your 85 VW has three common things I'd check first. 1. The O2 sensor wires crack and the sensor quits working sending the car into limp home mode. 2. the cold start injector at the end of the plenum/intake is a 5th injector that richens the starting mixture until the car warms up... it can fail and the car will run like **** until it warms up and runs on the 4 normal injectors. 3. Before the intake plenum, the can shaped thingy with the metal flap/disc you may have tried jamming a screw driver in or pushing open with your finger is a metal flap that controls and senses incoming air and regulates the idle mixture. It has a few position sensors. Don't poke at this part or you will muck up some parameters that are difficult to re-align. If this is it, take the car to a VW mechanic. That little bugger is a real pain.

could be the oil breather thats clogged up with oil or it could be the maf, try and see if that helps

yes it could be the cause of the problem