the mrs has a r plate uk 2000 4000 miles on full rebuild, hasn't missed a beat till recently. when driving every now and again it loses power and hesitates like mad and black smoke (prob un burnt fuel) out exhaust and the idle is erratic sometimes stalls. this problem is only now and again it'll be fine for miles and miles then play up for ten mins then fine again. i had the lamda changed, plugs leads etc idle valve cleaned and still the same and never puts any fault codes up. thinking poss maf but dont want to waste the money if its not that.
any help appreciated.

 

Do a diagnostics check to see what codes come up - could point you in the right direction....

 

Could it be a pipe sucking closed / seeping?

 

no codes. and all pipes ok.

 

Does it have an aftermarket dump valve? If it sticks open it'll do all of that.

 

no its only running the standard recurc tried blocking it off too and still no joy.