01 a4 1.8t APR 93 OCT reflash, custum intake, dahlbach diverter valve and boost gauge. Ok, so here is the problem about a month ago the car started turning off if i came to a stop or put it in neutral. It then gave me the P0411 secondary air injection system incorrect flow my SAI pump use to sound like a jet on cold starts then i started not hearing it anymore so i checked the fuse it was blown so i put a new one in cleared the code and the pump sounded weirder than before almost like a small exhaust leak and a couple weeks later i didnt hear the noise anymore but the same CEL came up and on cold starts my lights flicker and the RPMs go up and down a little and it sounds like the pump wants to turn on and off on and off till it warms up. So i dont think its the fuse this time i think it is the actual pump. I know the MAF is good and i cleaned it too, since then it doesnt turn off anymore. I had replaced most vaccum lines and the little vaccum line that goes to the combi valve a couple of years ago so i dont think that is the issue. The main problem i have is that the P0411 keeps coming on and since then my car wont go over 10 PSI when it use to spike at 18 or 19. Also, would a bad secondary air pump cause the loss in boost?? I am stumped at this point, i would appreciate any help on this guys. Thanks

 

Have you checked for boost leaks?

 

not too extensively.....but yeah

 

Sai does absolutely nothing. It adds air to the exhaust on start up for emissions. Then it shuts off. Kinda like an egr. I highly doubt it triggers limp mode. And anyways limp mode limits boost more than ten psi. I'd look elsewhere. FYI if your sai is broke don't fix it. Delete it

 

ok, thanks for your input, im spiking at 8 or 9 PSI which i think is stock. Is there anyway my APR reflash went away? Because if i had a boost leak wouldnt it be boosting weird and at random PSI's and wouldnt hold at 8 or 9 PSI?

 

Not necessarily. If you had a cracked hose or pipe someplace that required 8psi of pressure to open the crack, it would hold boost up to that point and then stay open. If it was a big enough leak it could limit your boost in that way.

 

A boost leak will act according to the size of the leak itself. In some cases it might be only a few psi lost, others it might not boost past 2psi. Only way to tell for sure that this isn't the cause is to perform a proper boost leak test.

 

how do i do a complete boost leak check?