boost problems

[jpresto]

I've got an audi A4 1.8t Quattro, recently the car went into limp mode, i think!!, i have lack of power and heavy steering, i took the car to a (useless) garage who plugged in the diagnostics and said there where 3 fault codes but they meant nothing so he cleared them, 3000 miles later had the fault code P0411 Secondary Air Injection Incorrect Flow.. a garage replaced 2 vacuum hoses, still not fixed, then audi diagnosed faulty air flow meter and temp sensor, i replaced them myself and also replaced diverter valve, i also disconnected the batterry for 30 mins, would the mis allign the throttle bodies..?? ive got a slight misfire only on cold starts, also i replaced spark plugs and oil breather hose, problem still not fixed 6000 miles later, sooooo frustrating.. pls any1 got any ideas.. thanx in advance...

[a8 tech]

I would suspect the fault code was insufficient flow and this will only be active from cold start as the valve shuts off after warm up phase.Ok if your losing boost you need to look for under boost or boost limit exceeded.Check fuel pressure and boost readings as well as turbo actuator free movement,slight misfire/hesitation may be a secondary stage coil pack issue or more simple throttle body clean and re-adapt.Post any fault codes and mvb for boost, misfire counter and throttle body readings for air gap

[jpresto]

thanks a8 tech, I'm gonna book it in for vag com diagnostics check next week.ill get them to check the things you mentioned.

[jpresto]

just returned from the garage, only 1 fault found on vag com: it was p1292/17700 Map Controlled Engine Cooling Thermostat (f265): Open Circuit
the mechanic said this would affect performance and would solve the problems if replaced.. is that correct?? i was also told the throttle bodies cant be adapted untill the faulty cooling thermostat was replaced..

[a8 tech]

Interesting, I would suggest the stored fault code requires attention and in theory if a fault code is stored then adaption reset may not be successful.I wouldn't associate this fault type with a boost problem.

[jpresto]

would the failed map controlled engine cooling thermostat sensor sensor cause the car to go into limp mode?

[jpresto]

i had the thermostat housing sensor replaced, i drove fine for 1 day, now its driving bad again, when i accelerate i cant feel the turbo kicking in, i does sometimes but only one in ten times. could it be a fault n75 valve even though the are no faults present and stored on the vag com diagnostic check..