I installed a boost gauge today to see why my car sometimes shudders at full boost. First of all I seem to get full boost only if I start accelerating from below 2.5 krmp, e.g. drive at stady 1.5 krmp then floor it, on 3rd gear or higher. The boost starts building at around 1.8 krpm, reaches maximum 1.2 bar at 2.4 krmp and then suddenly drops below 1 bar. This is when it shudders. The pressure stays below 1 bar all the time and at around 4 krmp peaks a little higher then slowly dropping when the rpm's increase. All the time the pressure fluctuates +/- 0.1 bar or more.<p>The strange thing is that when I start accelerating at any rmp over 2.5 k, e.g. steady 3 krmp then floor it, there will be a short<br>kick of boost a little over 0.5 bar then the pressure settles around 0.5 bar and is fluctuating +/- 0.05 bar.<p>It looks like I may have a problem with boost control valve. Any idea how much it costs? Now all you guys with boost gauges, what kind of readings do you get in the same situation. Do you get same max boost not depending on rpm you start accelerating from? Is the pressure steady, not fluctuating? I will call my dealer tomorrow but I would like hear from your experience.<p>I have a Euro A4 with ABT 215 PS setup which probably should give at least 1 bar max boost. For those who prefer psi over bar multiply the values I gave by 14.5 to get psi. BTW the temperature outside was 18 C, that is 64 F, if it matters.

It sounds like you may have some software problems. If this is something that just began when you put on the ABT kit then I strongly suspect this is the case. My guess is that you are hitting one of the several limits in the software that will set the boost frequency valve to 0% (no boost) at a specified max load. The symptoms will be a rapid cut of boost level for a moment until load decreases below the threshold and then boost will come on again. This pattern will repeat and if you are at full load then this will feel like a shudder as you describe. I would talk to ABT if this is something that began when you installed their kit. Otherwise, it could be a number of other things that would be easiest to diagnose with a VAG tool or similar. BTW, boost pressure is not measured by the Motronic system, rather the computer uses load to calculate the correct opening of the boost frequency valve. So boost pressure will fluctuate to some degree depending on RPM, gear, load, etc. HTH<p>Brett<br>APR