for starters stop overlooking the fact these codes keep coming back and fix the root of the problem....the first code is a gross evap leak......check all your vacuum hoses for breaks or tears and also double check every check valve as they can fail. Another thing you can do is disconnect the top line from the BPC and plug it with a bolt and see if you notice any difference.Ok on my 2001 Saab 95 I have been getting P0455 and P0420 since last month or so, I replaced the Gas Cap, 2 times already since I have been getting the code P0455 and Cleared the codes with OBD2 several times, but they keep coming back after I drive about 100 miles, so I kept driving it as is,
But last Friday when I was driving on long Route about 200 miles, and while car was on cruise at 74mph , the cruise got Off automatically, I tried to put it back in cruise it did not engaged, so when I returned back home late night and noticed that on idling the RPM are little above the normal, sounds like Throttle Body Limphome mode, on that night did not get chance to check engine codes, next morning my wife drove it for about 20 miles to local store, and today in the morning i started the car again the Idling RPMs were little below normal, and I checked the Engine codes, and I see P0455, P0420 and P1230 , so I cleared the codes using OBD2 , which shut down the engine, so I restarted now every thing is normal, but not sure for how long.
5 months ago I have replaced Throttle body (I bought uses of the eBay) at same time I also replaced DAC (bought from eEuroparts) , couple of other valves and rubber tubes were also replaced, so since those replacements it was driving fine without any codes, but I started getting P0455 since last month. Also replaced Turbo 2 months ago. and installed TD04 originally it had Garrat , since I replaced Turbo I never upgraded ECU program, could that be the reason for these issues?
changing the turbo without upgrading the ecu will not do any damage other than you will have more turbo lag when you boost up