I'm not an expert by any means, have owned my 156 2.0 TS (1999)for 18 months (mileage 30,000) and have been experiencing a minor problem with power where there seems to be an intermittent problem.
Some days she runs like a dream and is immediately responsive and others times seems just not to have that instant pick up, as though she's a bit flat.
obviously there may be more than one thing that could cause the problem but I think the most prudent starting point is to replace the plugs.
in relation to this I have scoured this and other Alfa sites, the internet in general and some specialist spark plug sites.
I think I have found some interesting information that anyone thinking of changing plugs may find usefull.
It appears that basically there are only 2 real contenders for plug manufacture, Denso and NGK.
Standard plugs are the NGK Platinum which very in price quite a bit, mainly down to supplier and are obviously fine.
Denso supply Iridium plugs which are apparently far better but which are about 50% more expensive generally.
The difference between the properties of these plug types can be seen on the following web site www.sparkplugs.co.uk
where there is a comparison chart with all plug electrode metal types listed :Iridium, Platinum, Nickel, Gold and Silver.
It certainly appears that the best all round performance will be achieved with Iridium, though as such they are relatively new to car use, being that they were actually designed for use in high performance bikes.
I discovered that for a set of 8 Iridium plugs from Denso you would expect to pay about £120:00. The only drawback being that of the set of 8 plugs, 4 will last 60,000 mls and the other 4 about 30,000mls.
I also found that NGK have recently started offering a similar iridium plug solution. NGK iridium plugs seem to be a really good option as there is no sugestion that the 2 banks of 4 plugs have a different life.
I found that the NGK Iridium are a little difficult to source and that of the 2 banks of 4, one plug is readily available whilst the other is only generally available from the USA. this said and with me not wanting to use a plug that is widely untested in this application I made enquiries with NGK.
They suggest that they have not fully tested the plug in general car use and though not implying there was any likelyhood of it being a problem could not as such offer a garauntee.
I hesitated at this point but when speaking to staff at Spakplug.co.uk they assured me there was basically no difference between the plugs supplied by Denso and those by NGK, the Denso ones being absolutely fine.
They also at present have stock of NGK Iridium for both banks of 4.
The suprising thing is that for the full set of 8 NGK Iridium plugs including garaunteed next day delivery in UK the price inclusive of VAT is £70:00.
I have ordered and recieved this set and will be having them fitted shortly and will of course report back with my findings.
For anyone interested the respective plug makes and part numbers are as follows: Denso, 4 x SVK20R-Z8 & 4 x IXU22
NGK, 4 x BKR6EIX & CR7EIX
Any thoughts or sugestions would be greatly appreciated.