no CEL but engine has no power and backfire
 

Boxster 2.7 (2000) - engine has no power and shake under 2000rpm, and sometimes backfire!!!

-CEL is ok, no OBD fault codes found
-gasoline usage normal (highway <8, city 12-15)
-CO test - more than 5% !!!
-have new spark plug, air filter and fuel filter
-when I take out oil cap - small underpressure and engine throtle a bit for about 2 sec and than back to normal run
-MAF - 6g/s by 750rpm,
-O2 Sensor 0V-0,86V
-LT Fuel Trimm about + 15%
-The Secondary Air Injection Pump- ok, but I dont know about valve condition

I really dont know what the heck is going on,
is it AOL ?, or maybe head gasket ?
Please help !

success !!!
 

I visit today porsche service, and they found that MAF is bad and ... with new one, engine has much more power at low rpm, and doesn't backfire any more, but now it is very unstable at idle. so after search they found one more problem - oil filer hose vacuum leak.

When I checked with my CRecorder, at idle 750rpm, the air flow is now about 3 g/s, LTB1 trim is + 0.78% and B2 is -0.78 so it looks much better now ;)

I have to wait few more days to replace that hose, and than I will inform you more about the effects.