Underboost Code

[SejRamkas]

What are all the possible causes of an underboost code? I've got an intermittent CEL showing for underboost condition and I want to determine what is causing it. I had a string of codes relating to the intake and EVAP purge valve along with the underboost code originally. I replaced the EVAP purge valve and intake manifold and cleared codes, but the underboost code remains. Like I said it is intermittent and really only shows up under heavy load uphill, car feels like it is still boosting under normal conditions.

I checked the wastegate arm and there is a little play back and forth perpendicular to the engine, but none forwards or backwards parallel to the engine. Is my wastegate loose and definitely to blame? Could it be some sort of a sensor or vacuum leak causing the issue?

I am looking to fix the car as cheaply as possible and then sell it due to all the issues I've been having and I'm starting a new job that will require 150 mi commute daily, but at the same time don't want to screw the next guy with a "band-aid" fix.

[wxsgt]

diverted valve usually and/or clean the maf. that's what did it for me

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[Alex1188]

What are all the possible causes of an underboost code? I've got an intermittent CEL showing for underboost condition and I want to determine what is causing it. I had a string of codes relating to the intake and EVAP purge valve along with the underboost code originally. I replaced the EVAP purge valve and intake manifold and cleared codes, but the underboost code remains. Like I said it is intermittent and really only shows up under heavy load uphill, car feels like it is still boosting under normal conditions.

I checked the wastegate arm and there is a little play back and forth perpendicular to the engine, but none forwards or backwards parallel to the engine. Is my wastegate loose and definitely to blame? Could it be some sort of a sensor or vacuum leak causing the issue?

I am looking to fix the car as cheaply as possible and then sell it due to all the issues I've been having and I'm starting a new job that will require 150 mi commute daily, but at the same time don't want to screw the next guy with a "band-aid" fix.

Wastegate should have no movement in any way. The only non band aid way to fix is to purchase and install a new turbo...

[o1turbo30v]

Wastegate should have no movement in any way. The only non band aid way to fix is to purchase and install a new turbo...

+1^ new turbo for about $1K and a Saturday with friends to install it.

[SejRamkas]

+1^ new turbo for about $1K and a Saturday with friends to install it.

This is what I was afraid of. Probably end up buying a used one and throwing it on before I sell it. Yeah it won't be a brand new one, but it should last the next guy long enough to give me peace of mind if I find a lower mileage one taken off for a k04...

[nycaudi]

Youre problem doesnt seem to severe yet... y not buy the clip that secures the wastegate rid...uou might be able to get away with it. Its only 15 nucks for tje clip

[SejRamkas]

Youre problem doesnt seem to severe yet... y not buy the clip that secures the wastegate rid...uou might be able to get away with it. Its only 15 nucks for tje clip

What clip are you referring to? I remember reading there was some such clip for the VW platform (jetta I believe), but nothing that fit the A4 to help with this. There was a cheap fix I read about cutting the wastegate actuator rod and threading it and using a threaded adapter to take up the slack, but this is a bit too much of a band-aid fix for me. Yeah I guess you can argue so is replacing with a used turbo, but at least it wouldn't be an obvious band-aid when it fails again (because lets be honest, these wastegates are crap and it WILL fail again...).

[nycaudi]

The clips are available for the 2.0 audis...its recommended to be purchased along with the latest revision of the stock turbo. Revision S. It just snaps on to the rod/swivel area and is meant to keep things tight. Just call your local dealer and have them gove you the part number ...its like 15 bucks but you can probably f8nd it online for like 10

[SejRamkas]

Riddle me this. Drove the car yesterday and this morning after it has been sitting for 2 weeks (trying to keep miles off it for selling). The car drove beautifully with no CEL at all. Car boosted as normal and drove like nothing was wrong. I've also noticed the car is more responsive with better low RPM boost when it was cold in "closed loop" mode as opposed to open loop. Typically this would point to a sensor, but is there something else the car does with boost control that changes once up to temp?

[bakedziti]

The CEL will come and go here. When I had this issue, I found (as most here will agree) that the CEL would be present on warmer or humid days that I really got on the throttle. The clip may work, but if you already have a gap between the housing and the wastegate, the clip won't do much to pick up the slack. I am by no means saying that it won't do anything, but it can really only do so much here.

I will have the turbo I used to correct this issue up for sale shortly, if you're interested.

[nycaudi]

Thats how my issue started...until i got the cel permanently. Sounds like youre in the early stage still

[SejRamkas]

Car definitely shows the CEL on warmer days after its been on the road a few miles. Definitely the problem based on the similar symptoms from both of you. Will be looking to pick up a used turbo soon.

[nycaudi]

Try to get s revision...thats the latest...and should come with clip already installed