Idle Stuttering on a cold start but fine once warm.

I've just had a newer engine put into my A4 and to puta long story short, we thought the last one needed a full rebuild because it turned out to be burning oil, I got a great deal on a low milage 2005 1.9tdi 128bhp (from a very trustable long time mate of my dads) so I decided to take it, but it turned out to be the turbo ******* oil into the exhaust (no symptoms other than blue-ish smoke), so I got a used turbo for now.

Now to the point. Its been stuttering (dipping in RPM) at idle on a cold start. If I go out for a drive and come back, it idles just fine. No loss of power that I've noticed (as quick and powerful as my last engine). No fault lights. The only difference I've noticed is that this engine runs a tad colder (about 5-10C) than the old one. That could be down to new coolant or something. That water pump and timing belt were just done on the newer engine too.

The chap who installed the engine for me said that it is something to do with the EGR valve (I can't remember exactly what he said). He mentioned doing something to it and it running fine and just told me to give it time to settle. I'm just worried because I had a similar problem to this and it turned out to be the original turbo and was sorted by replacing it with a refurbished turbo (the one that started ******* oil).

Anyone have any ideas? Could it be something to do with the EGR valve? Is the new (used) turbo at fault like the original. To be honest, my dad sourced the turbo on really short notice from someone who he hasn't dealt with directly before.

pauldazzle said:

Coolant temp sensor would be my first suspect. Often fails without throwing a fault code too.

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Would that cause a stutter though? It seems to be mostly fine on temperature. Once it's been run for a decent amount of time, it runs a hair below 90C.