They shouldn't go changing sensors.. since sensors generally help the car run more efficiently but they seldom make the engine management light flicker on and off, even if they failed completely.
The bump followed by the light coming on and the hesitation is at least consistent.. so the BBoB is the place to start, since even one corroded connector would do it, depending which it is).
My old Fiat 128 3P had a similar problem that affected dip/main beam... the friendly auto-leccy man completely re-connectored (new insulated spade connectors and then shrink-wrapped) the connectors to the relay... the problem was where the copper wire joined the connector, not where the connector connected to the relay... so that's why you need to take each connector off and have a good look at it.
It's interesting you had the same symptoms with the lambada.. The lambo' should last for years unless you feed the car leaded petrol, or dropped it on the floor while fitting it.
What kind of lambo' did you fit? Does it have an integral block connector (£100) or does it have just bare wires which had to be spliced into the existing wiring .. i.e using the old block connector and upper wiring (£30)? In my experience these wires can also become detached, since the joint is made via an insulated crimped metal sleeve... and the wire tends to bend at this sleeve... and the wire can eventually break, since the insulation was cut away and some of the wire probably already had a score mark in it....
So. it may be you have a de-activating lambda.. though this would be an unusual one for sure..
Anyway... it's more likely to need an auto-electrician to sort than a grease-monkey.. but doesn't sound like you have a major component problem.. touch wood.. you just need to find out what's loose.