mk4 gti 2.0, 3 error codes, lean trim, ideas?

[leckford]

Hi all,
Well i bought a mk4 2.0 Gti a month ago (had a mk2 Gti as a kid and loved it). The mk4 is great, but 200 miles into driving it the MIL came on. The car still went well, aright MPG, no performance loss. So i continued driving it around and have now bought a vag com cable and downloaded the faults. I guess i could just take it into a garage to fix but i'm rather enjoying trying to track down the problem first so i don't get ripped by the *******.

So enough waffle, here are the codes:
16795 P0411 Sec.Air Inj.Sys. Incorrect Flow Detected
16521 P0137 O2 Sensor Circ.,Bank1-Sensor2 Low Voltage (intermittent)
17536 P1128 Long Term Fuel Trim mult.,Bank1 System too Lean (intermittent)

16795/P0411/001041 - Secondary Air Injection System: Incorrect Flow Detected
Possible Solutions
Check Fuel Pump Relay (J17)
Check Hoses/Pipes to/between Components
Check Secondary Air Injection Pump (V101)
Check Secondary Air Injection Pump Relay (J299)
Check Secondary Air Injection Solenoid Valve (N112)

17536/P1128/004392 - Fuel Trim; Bank 1 (Mult): System too Lean
[edit]Possible Symptoms
Malfunction Indicator Light (MIL) active
[edit]Possible Causes
Mass Air Flow Sensor faulty
Oxygen Sensor Control faulty
Fuel Injector(s) faulty
[edit]Possible Solutions
Check Mass Air Flow Sensor
Check Oxygen Sensor Control
Check Fuel Injector(s)

couldn't find too much info on the P0137, but i'm assuming it's a poor reading from the lambda probe. There is an interesting page here http://wiki.ross-tech.com/index.php/Fuel_Trim_Info which discusses the trim / mixture. The bloke i bought it from had the MAF replaced just before i bought it, so i'm hoping it's not that. I think i will try to test the MAF as discribed in the trim page - record the trim output with vag com whilest i wind the car to the red line in 2nd.

I'm basically a complete but willing novice, hey everyone has to start somewhere ey! but from looking at the 3 errors i can't figure what the likely problem is, MAF, injectors or lambda. Can anyone looking at the codes give me they opions / insight. If i take it to a garage i want to be as clued up as possible.

btw, i've cleared the codes and they have not come back, tho i was too knackered to drive the car hard on the way back, so i've not had the rpm up over 5 yet, which from the trim mult error i'm assuming is when the error is occurring.

Sorry this post is turning into an essay, but something i've noticed when i have reved the engine, there seems to be no/little increase in power at high revs, nothing like the 'surge' my old mk2 gti used to have. thats prob due to the lean mixture..?

[leckford]

sorry another quick question. My MIL comes on with the ignition, and then goes out about a second or two after starting the engine. Is this correct? I've cleared the error codes but this still happens, just wondering.