fuel over rich selespeed
hope someone can help. My W reg (2000) selespeed 2 litre ts has developed a fault which appears as an overfuelling problem, most noticeable at low speed around town when the car idlespeed is erratic and you can see the exhaust and smell as though there is far too much fuel. When I bought the car the thermostat needed changing, and I never noticed this idle problem then - perhaps as engine temp was stuck at 50degrees. Anyway new thermostat fitted and swapped over old temp sensor. Noticed then that the connector (loom side) to the temp sensor was corroded and broken so got a used three pin one from an alfa at breakers yard and soldered it on. Temp reading ok now and car seemed to run better but after 100 or so miles its back to the stuttering/stalling round town situation. I changed the plugs for new and found the No1 well with oil in it, cleaned it out, new air filter, oil and filter and it ran good again for a week or so, then problem returned. Checked plugs again and they were all very sooty so cleaned them and put in again. I got some advice that the Lambda sensor may be the problem so I thought I'd do the diagnostics to check water temp reading correct and for any fault codes. Got a Vag KKL cable from Ebay, installed drivers from ross-tech site and supplied disc, got fiatecuscan version 1.6 and the current one. Now having a nightmare connecting to the ECU, I think I've got everything set up, com port, latency etc but after literally dozens of attempts to connect I got there once with Motronic Me 7.3.1 (outside EU version). This warned of incorrect ISO code (havn't found a correct one yet) and fault codes read engine speed fault, sensor fault and water temp reading of 208degrees. I thought water temp sensor could be problem until i checked air temp 400degrees!. RPM at MAR 69rpm, after starting engine went to 134rpm? Kind of reached the point where I just need to but and try temp sensor, Llambda sensor, MAF? etc etc. Also tried disconnecting MAF but car got very rough at idle.
Any ideas on cause of engine fault and why fiatecuscan is a nightmare?