hi i have a 2005 rrs with the 4.2 sc engine, just wondering what are the common problems i could expect on this car

I have the same car as you and from what I can tell, these engines are pretty good so long as they are serviced regularly.
It's the other bits we have to worry about!
I'm happy to stand corrected if anyone else thinks differently. 2016 RRS SVR Estoril Blue
2005 4.2L Supercharged Java Black - gone but was my first love.
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If we all point our RR's in the same direction and accelerate at the same time can we turn back time?

The petrol injectors clog up 2007 SUPERCHARGED HST

High-mileage 4.2 SC (as well as 4.4) can have issues with the timing chain, tensioners and guides. This is easily spotted by listening for 'clunking' noise on idle and - inevitably - check engine light with codes for "bank 1 and 2 lean".
It's the less catastrophic version of the 5.0 (SC) timing bolt issue. The bolts in the 4.2 and 4.4 are 6mm and they tend to bend slightly, which leads to the guides getting out of adjustment (or not 'guiding' at all), which leads to chain slack, which leads to valves opening and closing not in sync with the piston movement (hence the 'lean' codes).
The cure is to get a a complete timing chain kit along with guides and two new chains. Costs roughly $600 + fitting. Regards etc.,

Wojtek

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WAS: 2006 RRS Supercharged
IS: 2010 RRS TDV8 HSE