hi guys, this is strange one so dont know if anyone has had same problems, ive got a legacy gtb {2000} the problem is that on a run my revs drop as tho ive took my foot off the accelerator, normaly im at 21/2 revs and it drops to 11/2, ive had a new maff sensor and checked pipes for leaks, any advice will b very helpful thanks again guys

I might be wrong, but could it be a fault with the clutch/flywheel?

Its auto and that sounds expensive so hope not, it feels like the revs drop then go back up its a wired one haha

It's not clutch as if it was slipping revs would go up and then back down. Sounds more like going up a gear then down a gear. Any indication on dash ?

Could be idle air control valve, clutch switch or throttle position sensor. Have you run a diagnostic to see if any fault codes are being generated?

Yeah I'd check for any fault codes 1st could be a split or lose hose. as it's getting under a bit of load sucking more air in.  

Thanks guys, ill get it diagnosed to see if that makes things clear. I don't think its anything to do with the gearbox as it does it while its in park