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Discussion Starter #1
Just picked up this Jetta for my daughter, had a few issues, but most are fixed now. The only issue I have remaining, is it is hard to start cold. After reading some threads here, I have narrowed it down to the glow plugs or the circuit. On a cold start, the GP light only comes on for a few seconds and goes off and takes forever to start. After reading about disconnecting the coolant temp sensor, I disconnected it and tried again. The GP light now stays on for about 20 seconds and starts up fine. So what needs to be replaced or checked to fix this issue?
 

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As I've said in your intro there is no TDI Wiki yet.

You need to get your motor scanned (preferably with VAG-COM\VCDS) for any error codes logged in the ecu and post them, that will save a lot of guessing and check systems out.
 

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Discussion Starter #3
I just have an OBDII scanner at the moment, but no error codes show up and the check engine light is not on. Just spent $1600 on a tranny rebuild on my Dodge Ram, don't have any cash right now to buy VCDS or have it checked at at shop. Daughter just started work, so when she starts getting a check, she's gonna pay for that. Posted here to see if anyone had a pretty close guess to what it could be. Glow plugs and harness tested fine, not sure what the readings were, had my brother-in-law come over and check. He had a manual and checked the specs and said everything was good, just wished he had VCDS to hook it up to as well.
 

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I dont have a specific answer for you...just some TDI general information. The glowplug light and system on the VW is not the same as an American diesel system. If the GP light comes on, the car knows that it's cold enough to need them and energizes the plugs. The plugs will heat for 20 seconds, even if the light on the dash goes out after only a few. What I do is turn on the ignition and wait 15-18 seconds and then try to start just before they go off. If it is really cold, I will let them run for the full 20 seconds, turn off the ignition and turn it right back on, and try to start during this second heat cycle. Just try letting the plugs get good and hot before engaging the starter, before going crazy trying to "fix" the system. It may be working right...maybe you're just on the starter too soon.
New Bosch or Beru glowplugs definitely make a difference too. The Champion plugs I got local were junk!
Hope this helps.
 

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Discussion Starter #6
Went out today and tried again. This time the GP light stayed on for about 8 seconds and fired right up, today, the temp was it was in the 80's. When it was colder, like 50-, the light would only stay on for a second and go off and was hard to start. Maybe it's just the coolant sensor bad and when I disconnected it the other day, it reset or made better contact perhaps. Coolant sensors are cheap, will go down in a day or so and get a new and see if that makes any difference.
 

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You're guess may be accurate. 8 seconds at 80 degrees is unusual behavior. This is where a VCDS would be handy, the car has several temperature sensors.
 

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Discussion Starter #8
Ok, so the car finally gave me an error code of P0118, which is faulty coolant temp sensor, so will be going down and getting a new one and go from there. Will give update if anything changes.
 

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VAG Error Code: 16502/2778/11718/6498/000280

EOBD II Error Code: P0118

Fault Location:
Engine Coolant Temperature Sensor (G62) - Signal too High

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) active.
Difficulties with starting a cold engine.
Starting the engine when engine is warmish or warm, idle rpm immediately is 1200 - 3000 rpm.
RPM at idle is irregular.
With all engine temperatures idle rpm will often vary between 900 - 1000 rpm.
With engine warm (90 °C) the engine temperature suddenly drops (70 °C) and slowly comes back to 90 °C.
Bad acceleration during warm-up.
Diesel Engines: Glow plug indicator may be on for a longer than normal time or at ambient temperatures where it shouldn't come on at all.

Low engine coolant level.
Coolant thermostat.
Wiring/Connector(s).
The electrical signal coming from Engine Coolant Temperature Sensor (G62) is too low.
Engine Coolant Temperature Sensor (G62).

Possible Solutions:
Check/Replace all faulty Wiring/Connector(s).
Read Measuring Value Blocks (MVB).
Engine Coolant Temperature Sensor (G62) >-40°C.
Check/Replace Engine Coolant Temperature Sensor (G62).

Special Notes:
In many cars between MY 1995-2002 the (G2/G62) had a bad reputation for failing often. The original (G2/G62) sensor is black and the improved replacements are green.

When is the code detected?:
An excessively high voltage from the sensor is sent to Engine Control Module (ECM).

Description:
The Engine Coolant Temperature Sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal from the Engine Control Module (ECM). The modified signal returns to the Engine Control Module (ECM) as the engine coolant temperature input. The sensor uses a thermistor which is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases.

As taken from my new Free EOBD II Error Codes software
 
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