another 17705 error code problem!

Hi guys, I know this post has been mentioned loads of times but I have a problem with mine that's a bit different. I have changed the bottom intercooler pipe, cleaned throttle body, tried an atmospheric dump valve, checked all the pipes and cleared the codes for it to come straight back. My problem is that if I unplug the airflow sensor it doesn't go in to limp node and is slightly better running, I have now fitted a known working maf with no success, it still goes in to limp mode again. I also noticed the plug for the maf only has four cables (the fifth slot is empty) but the maf has five pins, could this be a problem? It is an aum engine code. Many thanks for any help