No boost at cold startup

I have a 2006 tdi,dsg,20,000 miles. At startup in the morning sometimes there is no boost. You pull over ,shut down and restart and it runs perfect all day. Only seems to do it on cold startup. Been back to dealer twice and going back a third time next week. Any ideas?

There's not supposed to be boost at startup.

You need to describe what exactly it is doing (while stopped, driving, etc) and how long after startup this takes place.

By cold startup I mean after driving a short distance,500-1000 feet, you cannot pull out into traffic safely. Slowly picks up speed. You pull over and restart and it will take right off. It will not happen the rest of the day,only first thing in the morning.

If you do try to get it to accelerate, do you get a lot of smoke? Any other symptoms?

dont go back to the dealer. remove the egr valve and check it. its most likely stuck open.

wrenchman30 said:

dont go back to the dealer. remove the egr valve and check it. its most likely stuck open.

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I agree with the don't go back to the dealer part, but why would a stuck open EGR valve cause no boost? And why would shutting off and restarting the car cause the egr to become unstuck?

if the egr valve is open any at all when boost is needed the boost goes the path of least resistance. into the egr side. the egr valve is spring closed. motor opened. the shaking of the car starting is closing it. just a theory. i guess i should post some pictures of it.

wrenchman30 said:

if the egr valve is open any at all when boost is needed the boost goes the path of least resistance. into the egr side. the egr valve is spring closed. motor opened. the shaking of the car starting is closing it. just a theory. i guess i should post some pictures of it.

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By that theory, whenever the car requests boost it would all go through egr valve, and the car would never have any boost.

When you try to accelerate it just runs flat, slowly picks up speed. No smoke at all. You stop, shut down, restart and it runs perfect and will not happen again until the next morning. Still under warranty so I'll let VWOA deal with it for now. Thanks for the response.

dirtdub said:

When you try to accelerate it just runs flat, slowly picks up speed. No smoke at all. You stop, shut down, restart and it runs perfect and will not happen again until the next morning. Still under warranty so I'll let VWOA deal with it for now. Thanks for the response.

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I would suggest that taking it back to VWOA is not the wisest course of action... Did they fix it the last two times? What makes you think they will fix it this time?

Sounds to me like limp mode is being triggered. Any guru's want to chime in?

Do you have any code information? It seems as if it should have thrown a code.

Can you get someone with a VCDS (VAG-COM) to check it out when it is cold, for the first start in the morning? Take a look at measuring block 43 and see if the turbine goes to 100% as soon as the car is started on that first start.

They can also get any saved DTC's (codes) for you.

You can find someone nearby in the TDI 101 forum, sticky thread.

http://forums.tdiclub.com/showthread.php?t=191421

If I had to guess, I would bet sticky N75 vacuum solenoid valve. Just a SWAG - not intended to suggest action to replace it (at least not at your cost.)

The codes and VCDS would tell us more.

Dan

DanG144
Dealer has replaced n75 solenoid on first try. On second try claimed erratic voltage going to ECM from manifold pressure sensor. Did throw codes but did not tell me what they were. Found corrosion on terminal from sensor to ECM. This time they are going for a wiring harness!

just keep letting them replace all the expensive stuff. Just ask for the old "broken" things to be put into the trunk.

let me see if i describe your symtoms. low power. if you hold it on the floor you get cloud of black smoke, engine knocks (like a gas pinging) then all of a sudden all kinds of power after several seconds. idles just fine. starts just fine. has dealer already replaced o2 and maf sensor. if this describes your car remove and clean the egr shaft of carbon. three t25 screws, valve has part number ending in 502. screws face the firewall. trace the intake hose follow on up intake about 4 inches look down you will see the valve. stand on passenger side facing the driver side.

Wrenchman
No smoke ,no strange noises, just runs flat. Will eventually bring the car up to speed but no power at all. Shut down and restart and runs perfect. Only does it on first start of the day.

Update to no boost

Well the car went to the dealer and was worked on by the dealer service and VOA service tech who was also there. Diagnosed intermittent voltage from pressure sensor to ECM. They kept the car and rewired a lot of the wiring harness. They found bad pin connectors . They drove the car through complete drive cycles for a few days. I got it back and has run perfect for a week. They gave me a rental car at no cost so I have to give VOA an ATTA BOY as they really get knocked around on here sometimes.