Hopefully someone can help ?

I have a 2wd saff cos and has devoloped a boost problem i think it is the amal valve but not sure? It should hold 23.7 psi,i have a didgital boost gauge that works fine,but the boost is suddenly all over the place will run perfect then drop boost to any level (say 11psi) come back on drop to (say 16psi) (you don't need the gauge to know ,you can feel it)come back hit overboost etc.The connections seem ok, if you unpulg the wires then plug them back in the valve will click,does this sound like a knackered amal valve??

Main problem is that i'm off to the ring on thursday and have 3 14 hour shifts to do before then.

Thanks for any help or advice

Rich