166 Engine misfire.

The engine warning light came on today. Took it to a garage with a diagnostic machine and it came back with the following codes:-

PO300
PO301
PO302
PO303

In other words the rear bank is misfiring. The car drives great its just the idle is lumpy. You can feel the judder at idle. On the move the car is smooth as silk and revs to the redline with no fuss. My car has done 53000 miles and has been very well cared for.

Car had major service at 41000 miles which included cambelt, sparkplugs and waterpump. Previous owner also had light come on and had three new coils fitted to the rear bank. The car has also had a new Airflow meter fitted last month.

So there we have it. Spark plugs, MAF and coils have been done, so whats causing my 166 to misfire on the rear bank?

Any suggestions/advice would be greatly appreciated.

From symptoms it sounds most likely that air inlet tube may be cracked, usually at the left turn 90 deg just before the throttle body, underside. The crankcase vent pipe dumps oil on this part of the rubber tube and it perishses. You can usually only see it by taking tube off. Not difficult and a temp repair with duck tape will confirm.
New pipe not cheap as you have to buy whole air box!!!
Are you sure the rear sparks/coil packs were replaced? Rear bank is a real pig time consumer compared to front. Mine weren't replaced by dealer despite being billed time and parts at 60k (NGK plugs have a code stamped on which allowed me to identify with NGKs help that they were the original spark plugs...)

any joy midlife?

Not had the chance yet. The pipe is connected to the airbox with a very tight fitting round clamp. Its not the usual 'O' clip type thing with the screw to tighten it up. Are these clamps factory originals or do the dealers/specialists have a secial tool to remove them. Im afraid that if i remove it i wont be able to get it back on again. Interestingly the new maf is connected using the standard 'O' type clamp with the screw thread at each end.

Does this mean the airbox pipe has never been disconnected from the throttle body? So how would someone replace the sparkplugs and coils without removing the throttle body?

a pair of woodwork pincers is all it needs to do them up again, special tools/pliers are available for about £5, but they do not get nails out of wood

Ok this is getting more confusing for me. I had a service on the car a week ago and the garage doing the work had to order a pollen filter for me. I took the car in today to have it fitted and mentioned that someone on this forum had suggested a leaking air inlet tube. The garage owner said that was easy to check for and hooked the car up the the emissions analyser because he said that can tell them alot about a car.

Guess what? The emissions are spot on! No air leaks upsetting the emissions then. He said engine running fine and revved the nuts of the car and couldn't detect a misfire. He agreed that engine is slightly lumpy at idle but he thinks it might be the engine management that is at fault.

Would an ECU reset help and if so how do i do it?

A small air leak will not show up on any diagnostics. The only air mass/volume sensor is the maf. The possible tube split is post maf so it won't show up, especially as the alfa diagnostics is very crude (compared to say Vag Com)
The air pipe clips can be done and undone with any fine nosed, wide spaced pliers. I find a standard plumbers compression joint type pliers fine once you have the knack.
Get in your engine bay and have a good look.
Remember there is more collective knowledge on this forum than ANY dealer.

Midlife, the simplest way to check is to wrap Rubbaweld Self Amalgamating Marine Tape round the full length of the rubber air inlet pipe, making sure they overlap and are very tightly fitted. If this stops the misfiring, then you will know where the problem lies. If not, then at least you have eliminated that potential cause.

Ok here is the latest. After spending a few hours on Sunday night trawling the forum i decided to reset the idle actuator and reset my ecu.

All I can say is wow, what a difference it has made to the car. The engine still has a slight judder but nowhere near as bad as it was. The car pulls very strong through the gears now and fuel economy seems to have gone up a few mpg as well. Before i bought the car it was owned by someone from London so whether the ecu adjusted itself to stop-start traffic might have something to do with it. The car feels so much better im really impressed!