Okay I had my motor rebuilt s5 na it idles great with out the mass airflow (maf) sensor but when i plug the maf in it dies. Everything seems to be plugged in right. Does anyone have any ideas??? I'm afraid to drive the car because with out the maf the ecu can't determine the proper a/f ratio. Or can it? I just don't want to run it too lean and blow the car up. If it helps the six-ports are wired open. Yes I know about the crappy low end and poor gas mileage but thats ok.

 

I'm surprised it runs at all without the AFM (not a MAF) plugged in. Did the engine ever run with this AFM? You can test it per the FSM to see if it is within spec.

The AFM doesn't determined A/F ratio; it measures incoming air volume, which the ECU uses to add/subtract fuel from the base map. You could very well run leaner than you would like without it plugged in.

 

I took the currant afm out of another running s5 na. Idk what to do should I just buy a piggyback to determine my a/f ratio??

 

With the AFM connected go to the Circuit Opening relay and put a ground to the Brown wire and try to start the car and see if it performs better. There should be a Black wire in the relay that you could use as a ground to jumper from. I'm famiiar w/S4 wiring so if the colors mentioned don't jive w/your wiring then report back and I'll search the S5 FSM wiring for you.

If this doesn't help you could remove the plug to the AFM and Boost sensor and w/key to on take a voltage reading from the V ref wire at the Boost sensor and it should be about 5 volts. Then reconnect the AFM and check the Boost sensor V ref wire once again w/ key to on and see if it changes. If the voltage drops then that would indicate a short in the AFM.

Lastly, is the newer AFM from a like S5. N/A to N/A or turbo to turbo and not mixed.

 

My FC had a very erratic idle and it was a rusty spring and cable below the intercooler: it wasn't getting back to the proper position because the spring has lost a bit of it's strength and because of lack of lubrication... Maybe you can just simply check that... who knows?... it was really simple to solve, but not that easy to discover in first place.

 

The currant and all the afms I have are all s5 na