Some technical advice please?
I'm trying to get my head around MAF sensors, EGR valves and so on, but my technical knowledge is a bit lacking (an under statement). To try and cut a long story short ......
I have a 159 SW 1.9 jtdm. Drove faultlessly for best part of 60,000 miles then developed the obligatory EGR valve blockage/failure poor performance resulting in a new EGR valve. These problems all disappeared with the old valve, but a new, unseen problem reared its ugly head. A hesitation, stammering miss-fire like problem, most noticeably in 2nd, and 3rd, but also causing a 'hunting' (especially with cruise control) at motorway speeds. Not always there, sometimes barely noticeable, other times awful. A couple of return trips to garage did little more than MAP clean, forced re-gen, test drive, no faults shown, no faults found. Problem still there. After seeking advice from this forum, started to look at MAF sensor. Removed it, and cleaned it myself, no change. Found another one (same part number, genuine Bosch etc.) from a dis-mantled same year vehicle. No change. Once again, have just un-plugged the MAF sensor and car drives absolutely fine (but with no cruise control). So this is where my technical under-standing starts to fall down .........
It seems mighty strange that a MAF sensor would work fine prior to an EGR valve change and then start to fail straight after, and too much of a coincidence to fit another (albeit used) that gives the same result. When the MAF sensor is dis-connected, does that stop the EGR valve from working, as in the EGR valve adopts a fixed position (with no MAF information to work from) in which case perhaps the MAF sensor(s) are working correctly and the new EGR valve is not functioning as it should when it receives the information?
Or is it as simple as failure of the MAF sensor(s) to give the correct info to the new EGR valve, and the new EGR valve will not work correctly until it gets its info from a NEW MAF sensor?
Just to restate, the car drives perfectly when the MAF sensor is un-plugged.
Thanks for any technical advice. The more I can get my head round this the more information I have before I return to the garage for a 4th time.