Return of elusive the thermal boost cut problem.

[Hy Octane]

Ok Hive mind..Was Hoping it was just the faulty thermostat, but not that simple.. It never is..
I need some assistance here.. What components of this engine have the ability to cut the boost down a step when it gets too hot?
No codes thrown, after running at temp for awhile, if I stop and let the engine idle for a few minutes say like I'm in a line at In n Out or similar, it builds up heat and when I drive off again, (especially if the ambient temp outside is 80's/90's) the boost will cut upon acceleration. Stopping the engine and restarting resets the boost until the temp causes it to cut again, usually within a minute or so..The whole motor seems to be running hot but the gauges are all normal.. // the cooling fans seem a bit busier than normal as it takes a few minutes longer before I switch off to let them cool the motor and stop//..
Ideas?

[lswing]

High air intake temp will cause timing to be pulled as the engine protects itself from the less reliable detonation, resulting in cut boost (something like that). Do you feel "bumps" upon accelerating, is this what your boost cut is like? If so, a changed tune and W/M kit fixed me up. My car would cut out on warm days, not on cool winter days, and is fine all season now...

If you could VAG-com and log your data is might be crystal clear once we look at the numbers. Good luck, hope this helps a bit!

[SteveKen]

Boost cut can be a result of limp mode. So anything can can throw the car into limp mode could be the issue.

Do you run a full scan with vag-com or just on the ECU? Could be caused by the transmission, etc.

I've heard (not confirmed) of faulty or improperly bypassed engine mount solenoids can cause the car to cut boost.

Might be a bad ECU, too. Is it chipped? You might want to reflow the solder pads on the eeprom. I had an intermittent issue with a spare ecu that seemed like it would only happen when it was below 85 degrees outside.

[marklar182]

Not engine mounts, I ran for a year and a half with a bad one that had a hard error logged in Vag-com, and never had boost issues.

[4everRS]

Agree with Mark above. Not a motor mount. I've been through that. No cut in boost.

You might have just got a bad tank of gas. Unless you've been dealing with it for a few tanks.

Data log it during the conditions it happens.

[Hy Octane]

Had the tech drive around with me while this was going on. There is absolutely no indication anywhere of anything amiss. No codes, no alerts, just reduced boost. We replaced the thermostat and water pump since I had noticed that coming home late at night the temp gauge began to go down to about 1/4 // The gauge should always read straight up and never move unless the thermostat is stuck.. so we hoped this was the cause. but no..
Not bad gas as this has been happening now for a few months.. And it has been runniing just fine in hot weather until recently.. theres some sensor or something that is faulty again.. I really dont want to have to pay for hours of diagnostics, so I'm trying to get a list of things that can cause the boost to cut due to hi temps and see if we cant narrow the search down from there. when Audi was paying for this a few years ago, they just kept replacing things until they accidentally fixed it. Then, it was a sensor in the climate control that was causing it.. now I dont want to pay for this tecnique.. hoping to be a bit more scientific about it..
but getting really fed up...

[lswing]

Vag-com it, that's what you need to do...could be the n80, regulates boost right?

And I don't mean look for codes, you need to log data and see what your boost numbers are, and other conditions at the same time, it's easy, just takes a bit of time...

[marklar182]

I haven't went back and read the history, but has the coolant temp sensor been replaced? If so was it with a OEM or aftermarket?

[SteveKen]

Thanks for the confirmation on the mount solenoids. I'm guessing that the default (broken) condition is stiff?

Anyway, the engine coolant temp sensor is easy enough to replace. You can always log the output to see if it's in the correct range, as well.

[4everRS]

N75 is the turbo frequency valve. It should throw a code if it's bad. Not a bad idea to check it.

Vag com it. Playing guessing games is a waste of time.