Idle dropping off but not stalling revs and drives fine

Idle speed needs to be adjusted to give more revs,

This can be either an engine management issue (bad idle air control) or a transmission issue if an automatic trans (torque converter lock up problem). Idle air control can often be cleaned so = cheap fix. Trans problem not so easy.

Is the engine idle just set a bit low anyway? Can you access the idle adjustment and turn it up a tad? The sluggish drive may be in need of an engine service but a 1.3 is small for this car. Check out online car owner forums to see if others think so to.

run the fault codes and look for a problem in the MAF/MAP VAF sensor areas

Oxigen sensor. Check accelerator pot also, and fuel pump.

It could be an o2 sensor. When you are unplugging your battery it causes it to rereset and loose its memory. If the o2 sensor is going out it can cause false readings leading the problems you stated. You can take it and get it scanned you can do what I did and go ahead and replace all my o2 sensors. I figured since one when out, the rest wouldn't be far behind.

It could be something simple like bad spark plugs, clogged air filter, or bad gas. Start troubleshooting there first and see if the problem gets any better.

I would check your "idle speed control" ISC on the intake manifold. It may just have to be cleaned. An ordinary can of carb cleaner should do the trick if the pintle valve inside is grunged up.

Here is the cause of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.