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My Jetta Mk4 TDI engine is hard to start in the mornings when the temperature is down around 16° F. When you turn on the key it goes like it's going to start, but the idle remains down. I continue starting for even up to half an hour eventually idle goes up and start.

I don't know what exactly could be the problem. I have been asked to put new glow plugs, new battery, and also service the starter. All this I have done. Still the problem remains. I need some ideas. Please help me sort this problem.

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  • Is it a manual or an automatic? – dlu Jan 8 '17 at 20:57
  • When you say the "idle remains down" has the engine started, but either can't get up to normal idle speed (~900 RPM) or won't stay running? Or does it not start at all? – dlu Jan 8 '17 at 21:09
  • Please check my edits, it is a Mk4 Jetta (1999 to 2006)? Also, it might help to know the engine, there were two used: the ALH from 1999 to 2004 and the BEW (PD) from mid-2004 (IIRC) through 2006. – dlu Jan 8 '17 at 21:15
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There are a few things that could be going on:

  1. If the battery is cold, it could be unable to get the engine up to speed. On the ALH engine, and maybe the BEW there is a minimum speed before the ECM starts asking for fuel. I think it is around 500 RPM. So, if you're cranking slowly that could be the problem. Besides a cold battery, too heavy oil could contribute to slow cranking.

  2. The glow plugs may not be all working or may not be staying on long enough, this could be due to a damaged glow plug wiring harness or a faulty glow plug controller.

Things to check / try:

  • Clean your battery terminals and generally make sure you've got good solid connections for the battery and starter.

  • Confirm that the glow plugs are working – after a cycle you should be able to feel some warmth near each of the plugs. I'm kind of leaning towards this one, since each time you try cranking the compression also warms the cylinders and eventually they will get warm even if the glow plugs aren't working.

  • If you have a way to get a warm battery, try using that to jump the car. If you start easily with a warm battery it would be worth checking the CCA (cold cranking amps) rating on the battery and the actual output from the battery when it is cold.

  • Measure the starter draw (probably at a auto parts store or an auto electric shop) to see if the draw is in the expected range. Too high could mean that the engine is dragging (thick oil) or that the starter isn't able to spin freely.

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    On the ALH the min RPM for fuel is about 200 RPM. I don't have an exact figure. RPMs are dependent upon voltage maintained to the starter at crank time, in general. You might verify that the injector is getting fuel by loosening a pipe going to it, and watching for leaking fuel. The next diagnostic might be compression. – mongo May 3 '17 at 0:14

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