The 1.4 PD75 is basically a 1.9 PD100 TDI with a cylinder lopped off.
Additionally, the 1.4 has a wastegated turbo as opposed to the VNT on a 1.9 which spools up better and boosts for longer (without a remap, you can feel the 1.4 struggle a bit after 3k RPM). With a remap, the 1.4 does get better (100 - 108bhp), but you can feel it run out of puff after 3.5k RPM.
The 1.9 will happily pull to 4k RPM and with a basic remap will do around 140bhp. The tuning possibilities on the 1.9 are quite extensive if you have the cash. 200bhp is relatively easy to get out of the engine, and quite a few put out 250bhp.
The 1.9 TDI has a longer gearbox than the 1.4 (cruises at about 65 MPH at 2000 RPM in 5th, as opposed to 55 MPH on the 1.4), but the 1.4 is slightly better suited to city driving. With regards to MPGs, I can only comment on 1.4 TDI. I usually get between 40 and 47MPG in town and if I stick to the speed limit on motorways, high 50s isn't hard to achieve. Sticking to 60 MPH will see over 60 MPG, and the most I've ever seen was 71 MPG on a 55 MPH economy run between London and Peterborough. Drving it enthusiastically on the motorways / country lanes will still see over 50 MPG. Driving like you stole it (100 MPH plus) will still see get you mid to high 40s. Stop start driving really kills the economy on TDIs (30 MPG tops) and they take ages to warm up too.
The engines are as reliable as a wood burning stove as long as the timing belt and tensioner is changed every 60k miles or 4 years. Also, regular (10k mile max) oil changes using VW 505.01 spec oil are a must. No official interval from VW on this one, but it's best to replace the water pump at around 60k, or as close to when a timing belt job is done.
Parts are relatively easy to source. Common faults specific to Polo 9ns (not the TDI necessarily) are coil springs can be a bit fragile - my front ones snapped at 29k. They've been revised, but it may be good preventative maintenance to put on -30mm Eibach springs. Console bushes are a bit dodgy, but this can be sorted out with Polyflex or Seat Cupra replacements. v68 motors in the air con system play up too, but they're an easy fix (if you're competent with a screwdriver and can spare a couple of hours). Alternator sense wires are known to snap on TDIs (due to engine vibrations). Tell-tale sign is the battery idiot light on the cluster doesn't light up when you turn the ignition on (not starting it). Again, relatively simple and cheap fix.
That's about all there is. And FWIW, I'd recommend the 1.9. I'm not biased either - I've had (and still do) my 1.4 TDI sport for nearly 4 years now. It's fun with a map, but keeps me longing for a bit more.
Ash
