Here's a checklist compiled from various posts on this site:
LCR/Leon specific:
Uneven tick-over? Flat spots at 2,500-3,000rpm?
Is the MAF clean?
Engine code on a 225 should be BAM..., for 210s its AMK... Engine code can be found on front offside edge of the engine.
Can you check under the car? Is the under-tray still in place (these often get damaged/torn-off - £100-ish to replace)? Is the splitter present (if not, it's £25-ish at SEAT stealers & 'clip-on' fixing)? Check exhaust brackets are fully intact.
Check bodywork for paint-fade on yellow & blue (non-metallic) LCs/LCRs.
Boot lock work OK? (Simple/cheap fix.)
Evidence of water ingress in boot, under driver's/passenger's floor mats? (Simple/cheap fix.)
Check the rear wiper washer works fine and is not leaking into the boot. (Simple/cheap fix.)
Switch on the aircon and select 'low' for temperature. The radiator fans should come on but at a slow speed when using aircon. If the fans come on fast and loud then on/off then the fan motor resistors have gone.
Do the mirrors fold-in via the adjustment knob (turn to 6 o'clock position). Do they open OK when back to 12 o'clock?
Does the horn work correctly? If its tone is merely a feeble 'peep', then it's a front-bumper-off job to clean, reconnect & reposition (facing rearward) horn.
Does the car have a pukka FULL SERVICE HISTORY (aka FSH)? If not, walk way!
[*EDIT*] If the car has a retro-fit Audi S3 front strut-brace - Leon/LC/LCR & A3/S3 share same chassis - consider that if there isn't also a retro-fit rear strut-brace (a bar across the back seat, fixed to rear strut turrets), then the car will be prone to high-speed understeer (because the front-end will be much stiffer than the rear).
Ask the owner to take you for a drive when the engine is cold; if he/she then thrashes it from cold - walk away! Similarly, if during the drive the engine/turbo is given a good workout, & the owner then switches off without letting the turbo cool-down (ie allowed to idle for approx 60 secs) - walk away!
LCs/LCRs are generally robust & well-built, but can be pricey in the long-run if they've not been maintained or driven correctly.
General used-car checks:
If car is over 5 years old or accumulated 60k miles, it should have had/needs a cambelt change (also change water-pump to brass impeller on VAG 1.8Ts).
Brake pads - much left on them? Discs ok?
When warmed up, put in 6th at 30mph and put your foot down to check for clutch wear.
Gears engage correctly when driving in a spirited fashion (1st and 2nd especially)?
Check for play in steering. Car brakes in straight line/drives in straight line? [*EDIT*] NOTE: some LCs/LCRs can very slightly pull to the left, this is because the alignment setup is for LHD cars, which therefore compensates for driving on the right-side of the road (camber).
Is tyre-wear even? Tyre condition? Are all 4 tyres of the same manufacturer/type? If not, the car's handling will feel unbalanced.
Body alignment, dents, scratches etc. Crouch at rear & front of car & look along sides.
If the bodywork needs a wash, consider that the owner might be trying to conceal paint blemishes or fading (see ref to yellow & blue LCs/LCRs, above).
Any rattles (interior & exterior)?
Check all electrics, windows, fog lights (front & rear) etc, etc.
Fully open and close all the windows and check for any nasty cracking/twanging noises - the cables can snap and unravel inside resulting in the glass falling inside the door. Check that central locking works on all doors. Neither are massively expensive to fix but require stripping down the door and are a bit of a PITA.
Front light adjustment etc.
Scroll through trip computer, you may be able to see how its been driven... (mpg etc)
Check the CD changer & radio works. Check all the speakers work.
Check engine temp doesn't go over 90C.
Ask owner to show you where the oil dipstick is located; if they don't know, then walk away 'cos it means they've never checked, or care about, the oil level...
Engine bay: fluid levels; 'mayo' on inside of oil cap; check dip-stick - is oil level low; is oil old (black & treacle-like)?
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