Hmmm maybe this isn't an air delivery or ignition problem... Is your fuel filter very old? Have you tried fuel injector cleaner or Seafoam in the gas tank? What gap do the spark plugs have? How old is your battery (are you sure it is good?)?

Just some ideas.

 

Thanks, but I`m not sure that any of this things are the problem. Gap is good(0.028), filter too. I`ve done seafoam once 40k miles ago. I`ll see what guys at service say after testing. I`m still thinking something with air delivery boost/vacuum leak or bad MAF.

 

One more thing. What about catalyst converter, I think that mine is clogged to some degree, maybe making problems with back pressure. Is it safe to clear metal net inside of the cat so it doesn`t restrict air coming through? Emission is not problem here...

 

There are people who have "gutted" their catalytic converter. Just do it when it's off the car And it is possible for a clogged cat to cause problems.

 

Ok, but what about o2 sensor, I think there is one after cat? Will it cause problems without cat and give an error code?

 

You will get a check engine light because of "catalyst efficiency below threshold" or something like that. My car has that code right now... because of the high-flow cat. 034 Motorsport makes an O2 sensor spacer that should get rid of that code.

 

did u put a new air filter and try runing it without the mass again and see if it drops. if it still dose then you will know its not mass.

 

I`ve changed air filter. But when I unplug MAF, car is only boosting to 4psi like in limp mode, so it is hard to tell is it better. I`ll see if it drops below 4psi, because with maf it goes to almost zero psi after 5000rpm...

So only that code "catalyst efficiency below threshold" and I can ignore it, doesn`t it upset fueling or something?

 

It shouldn't do anything other than turn on the check engine light It's just a way for your car to tell you that its exhaust is producing excessive emissions.

 

Good news .

Car is normal again. The problem was pipe going into the Diverter valve. Can`t believe I didn`t notice that...

Now boost is fine. In second gear 11.5psi till 5000rpm and slowing fading to something around 8-9psi at 6000rpm, this should be just right for 0.8bar chip and 187HP

Thanks for help, it wasn`t maf after all. Anyway, it`s good to know that maf is worknig fine after 140K miles and other sensor are good.