To clarify, cold start meaning the engine has been sitting overnight, not necesarrily below freezing ambient air temp.

 

One suspect would be the CTS (coolant temperature sensor). There are 2 sensors in the part; one output is used for the gauge in the dash the other is used by the ECU to control the air/fuel mixture. It is not uncommon for them to fail. Can you read the temperature supplied to the ECU with your reader? VAGCOM/VCDS can do this so it may be available on your reader if you can find the right menu, etc.

 

Pretty sure I have seen this on my reader. Is the only reading out of the OBD II port the ECU reading? Or do I need to pick between the dash reading and the ECU reading?

In terms of the reading itself, what exactly should I be looking for?

 

Pretty sure I have seen this on my reader. Is the only reading out of the OBD II port the ECU reading? Or do I need to pick between the dash reading and the ECU reading?

In terms of the reading itself, what exactly should I be looking for?

With VCDS I think you can read either one based on which output is choosen. Check on that though since my VCDS has been down for awhile and I'm working from memory. Also, the output in most likely in degrees C so keep that in mind.

 

If the sensor isn't reporting ambient temp range on your scanner when the engine is cold, then the sensor is probably bad.

 

Duh. Should have thought for a second before posting

 

also while back there (coolant sensor area) pop off the "combi" valve and check if it is operational

 

What should I be looking for? Couldn't find anything after a quick search

 

Did you adapt the throttle body after cleaning it? How was the intake manifold cleaned? If removed, did you use new gaskets? While I also suspect the CTS, it's best to check everything.

 

Wow it's been a while.

Throttle body was adapted after cleaning. I left key in ignition for ~1 minute, heard the throttle body whine and stop whining. Then started.

Intake manifold cleaned with engine degreaser, brake cleaner, carb/engine cleaner, purple power, and a lot of water to rinse it out. I had to scrub for ~2 hours with a toothbrush to get it clean.

New gaskets: intake manifold to block and throttle body to intake manifold.

I will try to diagnose the CTS this weekend.

Thank you again for all your help.

 

I would connect the VCDS and see if this only happens when the air pump is running and what the CTS is reporting. Since you only have a code reader, you would need to find someone with one or buy the cheap version. The SAIP runs when the combi valve is open, so a blown combi can cause a vacuum leak. You can test it with a vacuum pump/gauge combo to see if it holds vacuum. The CTS is more likely and would cause hard starting now that temps are cooler. Again, VCDS will show the exact temp the ECU is getting from the CTS. I've had 2 fail recently (out of 3 Passats) and they both read about 248F when cold.

 

Thank you. I will start looking around for VCDS or maybe I will just purchase it.