As of this morning, my 997.1 Turbo (26K miles) boost will not go over 9 PSI... engine sounds normal, no CEL has been set. Only mod i have are vividracing straight pipes which had been installed last summer and never had any issues, stock tune. I will be taking the car to the porsche dealer on Monday, but would like to know what could be wrong. I did have my local garage Porsche tech look at this afternoon but he could not see anything obvious with it like loose hoses etc. He did not have a Porsche diagnosis tool to dig deeper. If someone has experienced a similar issue feedback would be appreciated... Thanks!

 

I am having the same issue - bone stock 997.1, tiptronic. Just got the car out of storage and it will not boost past 9 psi. No check engine light. Car seems to run fine at low rpms. Car ran fine before putting in storage. Am very interested to hear what you found out.

 

Turbo needed to be replaced ..... Sold car .... Good luck !