My car has a slight surging feel when I shift out of 2nd gear with light boost and light-med throttle input at around 3k RPM. The best way to replicate it is to let off the throttle right when boost is starting to kick in. Never happens in other gears and the car holds full boost at regular and overboost levels. Is this a boost leak? From what I understand, the car does not have diverter valves so is there some other type of blow off valve that could cause this?

 

The 997TT does have diverter valves. When I asked my local tuner (Cantrell Motorsport) about plenums and diverter valves, this is what he had to say:

"Generally the plenums have been very popular. Gains on the 996TT are around 30hp. I'm not sure exactly what the 997 is yet. Also keep in mind that your ecu needs to adapt to the new plenum so it might take a day or so to really make power. Doing a before and after dyno would really tell us what power they are making. Your car already has diverter valves. There are higher quality valves out on the market that are more responsive and work better with modded engines and ecu's. Your stock valves in your car regulates your turbo power. At idle, your valve is open from vacuum pressure. When you depress the throttle, the diverter valve begins to close. When fully closed, turbo boost is allowed to be delivered to your engine. When you lift the throttle, the boost pressure is released from the valve into your air cleaner box. Inadequate/defective valves have extended lag, loss of boost and sluggish throttle response. New diverter valves can fix these problems. The biggest issue with stock diverter valves is they cant handle a chipped/modified car because of the higher boost levels the valve has to work harder and faster and it simply can't.

FYI, all of the aftermarket diverter valves are better than the factory ones whether your car has been modified or not only because their design is more robust i.e. aluminum bodies instead of plastic, billet pistons with viton seals rather than rubber diaphrams, the ability to rebuild/service them, and the ability to change spring rates based on boost levels."

Back onto topic, I haven't noticed any "surging" from my car like you described but I'll give it a try using the methods you mentioned.

 

So you're getting a plenum?

 

Already have it...didn't you see my post about it?

 

Dirty MAF sensor already?