My older ST24 has this trouble few months back, I plugged in my Bluefin used its fault code reader and got a fault code P102 I think it was. This is dodgy MAF. What I did was to get some ISOPROPYL ALCOHOL spray (Servisol IPA 170) got mine from Maplins cost about £5-£6.

Give the MAF a spray and this spray cleans and dries instantly, best thing as MAF is a delicate thingy and well it worked for me.

Not saying this is your problem, but it worked for me and cheaper than a new MAF I'm sure.