Firstly hello!

I recently bought an s3 2011 and decided to change the spark plugs (ngk pfr7s8eg). Car now runs like crap. idle bounces and it makes a rattly sound at the right side of engine. pulled plugs 3 and 4 with 3 looking sooty on the insulator 4 looks ok. Have i manged to break one of the ignition coils? Have i done something much worse? plugs torqued to 20lbs per foot.

help appreciated!

Soot on an insulator would suggest poor plug seating - hope it's not cross threaded. The rattly sound could be blowing out of the cumbustion chamber.

If it is blowing it would run uneven too . 

 

 

Thanks for getting back to me. The plugs for 3 and 4 came back out and went back in fine so I don't think they are cross threaded, all the plugs went in no problem. I could stick the old plugs back in a see if it runs ok.

I have VCDS and although the check light is not on I get this for the engine (checked this morning):

1 Fault Found:
000256 - Mass Air Flow Sensor (G70)
               P0100 - 004 - Supply Voltage
             Freeze Frame:
                    Fault Status: 01100100
                    Fault Priority: 2
                    Fault Frequency: 1
                    Reset counter: 255
                    Mileage: 71730 km
                    Time Indication: 0

             Freeze Frame:
                    RPM: 0 /min
                    Load: 0.0 %
                    Speed: 0.0 km/h
                    Temperature: 12.0°C
                    Temperature: 10.0°C
                    Absolute Pres.: 970.0 mbar
                    Voltage: 11.938 V

Readiness: 0000 0000

 

Any one know how to test the MAF harness?

 

I would look at cleaning up electrical contacts and connections first - MAF would normally affect general running rather than misfire

http://wiki.ross-tech.com/wiki/index.php/16484/P0100/000256

Could be a red herring as I still would not expect to see soot on a new Plug - in fact any plug... You have any way to check if there has not been a helicoil fitted before? 

Are you sure you have not mixed up two HT leads?