Feels like stalling

Hi guys firstly thanks for accepting me into the forum,
Right my mum owns a 1.4 automatic Micra 2004 plate, she inherited it so really doesn't want to get rid, but she has been having a issue lately and the garage has told her it's going to be at least £700 to repair, so take a seat, make sure your comfortable, this could take a while.
About 2 months ago she was driving to Tesco and the car started hesitating, then stalled, couldn't get it started for love nor money, left it overnight night on the side of the road, went back to it the next day and it started up but was really lumpy, got it home and called a mechanic who supposedly cleaned the throttle cable and throttle assembly and all was well, then recently it started the rough running again so she took it to a garage where she gets it serviced every year and he's come back with a fault with the idpm (or ipdm or something like that) and it's uneconomical to repair, he says it is going to cost in excess of £700 to repair the idpm alone and that might not solve the problem, now I'm no mechanic by any means but after owning several escorts, imprezas and more recently a Audi S4 I've become relatively handy with the spanners, so I checked the plugs and coils, there was a blocked hose leading to a blue plugged sensor on top of the engine casing so I cleared that, run a bottle of redex through it it and it seems a hell of a lot better, but it still feels like it wants to stall, now I don't know if it makes a difference but it doesn't feel like it's going to stall when it's in neutral or park, only when it's in drive or reverse, the car is only on 64k miles is serviced every year without fail but my mum's heartbroken that she might have to scrap the car like the garage is recommending so here I am asking for advice on what else to check, there is no engine light, I've scanned for codes and there's no codes stored (only a cheap scanner but does the job) could it be something as simple as replacing the maf or idle control valve or is she really looking at a £700 repair bill for this idpm part. Sorry for the long post but I'm hoping to find out if this is a common problem as the garage seems to think the idpm fault is common, or if it's something I can repair for her
as far as i'm aware the most common fault on the '04 micra's engine was the timing belts, they repaired it on the facelifted models; my last micra was an '04 but manual and very similar to as you're saying it bounced on idle revs and would stall on start unless i gave it revs plus if i put the clutch in from anywhere above 1.5k revs it'd just stall. not start for a while, then start up. plus as you're saying the repair costs were just unreasonable, i was quoted £1k for a new timing belt so just scrapped it and got a newer one

worth noting it did the bouncing on revs thing for a good year or so before showing an engine light randomly one morning, can't remember what sensor had the issue since it was so long ago. sorry i can't help more :)