Rough idle when cold and hard starting?

Hey guys. Pretty new to TDI's. Know very little about them . But I'm not new to diesels. Anywho I've got a 06 jetta. Just had the timming belt kit done and had #4 injector replaced and new cam and lifters.

Car takes for ever to crank up when cold and the glow plug light only stays on for about a second. Dunno if that's normal or not as far as the glow plug light goes, but I'm sure that it shouldn't start this bad when cold. It also has a rough idle when cold. Seems to go back and forth between rough and smooth idle quite a bit before its warmed up, then it idles just fine. Any thoughts on this?

Check to see if your lift pump is operating correctly still. It'll still run due to the transfer pump off the camshaft but will have hard starts.

Maybe the glow plugs are on their way out, but not bad enough to trigger a light. They're about $30 each.



http://forums.tdiclub.com/showthread.php?t=2165

Did these symptoms occur before or after the timing belt change. Who did the work and did they use the proper lock tools and the VCDS for timing/torsion value setting?

It was running bad before everything. Sorry meant to put that in. It was vibrating at an idle and now that's gone. Assuming that was from the bad injector. So it's still starting hard After the timing belt change and the rest of the service. I don't know why they didn't notice it or never did since it had been sitting in a warm shop. The place that did the service is the only TDI Club approved service center in Utah.

So ruled out the lift pump. I can hear it come on and it's getting fuel to the filter with just the key on. So still trying to figure out the hard starting and rough idle when cold.

How many miles are on your engine? Why was Injector 4 replaced? Did you replace it? It sounds like it's losing its fuel prime.

Nero Morg said:

How many miles are on your engine? Why was Injector 4 replaced? Did you replace it? It sounds like it's losing its fuel prime.

Click to expand...

199,880. The shop I took it too said that injector was bad and the rest were good.

Could be a fuel prime loss issue, or glow plugs getting weak. Or combination of both. Glow plugs don't cycle on long when you do key on, but they do run when the engine is cold and running. I'd suggest starting there by replacing the glow plugs, if you still have hard starts may be time to replace the orings on the other three injectors.

Nero Morg said:

Could be a fuel prime loss issue, or glow plugs getting weak. Or combination of both. Glow plugs don't cycle on long when you do key on, but they do run when the engine is cold and running. I'd suggest starting there by replacing the glow plugs, if you still have hard starts may be time to replace the orings on the other three injectors.

Click to expand...

So possible fuel prime issue...... well it starts fine when warmed up so I wouldn't think that would be the case but I could be wrong. What controls the glow plugs? I could start chasing down that line?

Glow plugs are controlled by the glow plug controller. It's a relay lookin like box under the cowl panel, drivers side. And yes loss of prime usually takes sitting overnight to happen that's why it starts up fine warm.

Nero Morg said:

Glow plugs are controlled by the glow plug controller. It's a relay lookin like box under the cowl panel, drivers side. And yes loss of prime usually takes sitting overnight to happen that's why it starts up fine warm.

Click to expand...

Hmmm ok. I guess I could see that. I'll have to check out the glow plugs. Thanks for the info. I gotta get to the bottom of this.

Does the temp sensor have anything to do with the glow plugs as well?

CodyPD06 said:

Does the temp sensor have anything to do with the glow plugs as well?

Click to expand...

Yes it does. Glow plug glow cycle will be longer if temperatures are low enough. I don't remember what the threshold is, I think it's around 40°f

The temp sensor reports temperature to the ECU which tells the glow plugs when to operate. There a few temperature sensors, if you can read those with a VCDS type device when cold, then when warm, compare the 2, you'll see whack values if they're hosed. When it gets below 40 you'll notice the GP light stay on longer, the plugs continue to run after the squiggly turns off. Much of that can be checked electronically. Just to add to the confusion, your model had a recall for glow plugs and software, you may need to check you got a good set-up. All that being said, once started the motor should idle smooth fairly quickly with no glow at all.

Are you confident the shop set your timing correctly?

Did the mechanic do an injector balance with VCDS? I suspect a brittle injector wiring connection.