Ok so I changed the battery on my car a few days ago and OH MY GOD! it caused chaos! Who would have thought that simply disconnecting an old battery and fitting a new one could cause your car to run on no cylinders, 1 cylinder or 3 with crazy misfiring under load! I mean .... who would design a car that screwed its owner over by doing that?!?!!? .... love my car but man was I pissed when this happened!
The solution (VW will tell you) is of course to take it to a main dealer (might well be totally un-driveble in this state!) or plug in a VAGCOM diagnostic kit and realign / recalibrate the throttle body with the engine computer ... but ... this is not necessary and money / stress that you can save. In short, the car is capable of re-calibrating itself but only if you follow this exact procedure ....
1) Clean the throttle body - all information I could find implied that not doing this might result in a bad re-calibration so I did it and took the opportunity to clean the intake pipe too which golfs love to slowly fill with oily cheese. Regardless of the importance of this to the re-calibration process, it also helps with a smooth idle and has made a noticeable difference to a car which I thought ran pretty damn well as it was. It's a 45 minute job, including the cleaning, and removal of the throttle body itself is pretty straight forward though you will need an allen key set. Also required is a can of air intake cleaner from Halfords (£6.99), an old toothbrush and some rag that doesn't leave fluff or strands behind. Take care not to strain the butterfly mechanism which you'll need to hold open while you clean it and around it. The cleaner is excellent and literally goes through the grim like a knife through butter, great product. Also be careful with the air intake housing that bolts on to the throttle body. There is an MAF sensor in it and whilst you can spray cleaner in to the housing and get a rag in to clean out the crap, I would advise not to go anywhere near the MAF sensor even if it means leaving a bit of cheese around it. Its very fragile and sensitive.
2) Disconnect the battery - I read that it might need disconnecting for a few hours but (and I tried this a few times before i got it right) mine was disconnected on the successful attempt for less than a minute.
THIS IS WHERE THE PROCEDURE MUST BE FOLLOWED EXACTLY
3) Reconnect the battery
4) Turn ignition key to position 2, ie dash lights up, but DO NOT START THE ENGINE. - If you then stick you're head under the bonnet you will hear your throttle body performing a re-calibration routine, a small motor whine that doesn't last long. I have read let it do this for 60 seconds then leave it another 60 seconds. Time it and leave it for 2 mins in total.
5) DO NOT START ENGINE - just turn the ignition all the way off.
6) WITHOUT TOUCHING THE THROTTLE AT ALL - start the engine and let it idle for 10 minutes. Again, time it and just be patient, I did and it worked for me.
7) Switch off engine and ignition completely.
Final recalibration stage! .... Go for a drive - you will be gutted to find you will still more than likely have a misfire under hard acceleration but this drive is important as the car is still re-learning. It should drive fine with anything up to half throttle (ish). I drove 7 miles and parked it at a mates for a couple of hours while I watched the Joshua fight. On the drive home it was 100% perfect, smooth idle, full power, not a hint of a misfire ... sorted!! I am guessing the 2 hour park up is unnecessary it's just what I had planned for the evening. You should just be able to turn the engine / ignition completely off after the drive and then start up again and be ok.
All of this because I changed the battery ... f*** you Volkswagen! that is some proper dirty design right there which guts me because I love the car so much. It sticks in my throat that the designers would build something in to the car (or at least not bother to find a solution) that requires this much effort to change a battery .... mental!
That being said, it's always good to get to know your car and I kinda enjoyed fixing it because the solution was cheap, easy when you know how, and gave me the opportunity to show the car love by cleaning the whole assembly. Plus I get the additional benefit of the improved idle, but .... not going to lie, it was a major worry for me when this happened and is just so unnecessary. Hope this post will save some of you guys and gals from the same inconvenience / stress! You can fix it yourself easily!!
