Corsa D (59) 1.2 SXi - Lumpy idle since misfire

[WoodsterT]

My corsa had a misfire a few weeks ago. Breakdown called, error code P0304 (No.4 Cylinder Misfire). Took it to my garage and initially they replaced the coil pack but this didn't sort the problem so they put the original coil pack back in. This was when they then discovered the camshaft had snapped from the bearing support, which was the cause of the misfire. They replaced this and all was sorted (The spark plugs were replaced as well of course, I got them to give the car a major service whilst it was with them as it was due anyway.)

However since I've had it back, it's been idling very rough/lumpy and feels like it wants to stall (you can see the interior lights dimming ever so slightly and feel the little hiccups through the seat) - there's no loss of power though and it still drives as it should, and the lumpy idle only 'starts' after a few minutes of the engine being on so it isn't instant UNLESS the engine was on recently (IE a few hours ago.), if it's been a long time or overnight the idle is fine for the first 2-3 minutes..

I took it back to the garage to get them to diagnose but they couldn't find anything (no error codes stored, no warning lights etc.) and from their perspective 'mechanical-wise' everything is working as it should be.. so it seems it's a Vaux specific thing that I'll need to visit the main dealers for. Just wanted to see if I could get some opinions/advice on here first as to what I could possibly look at before I take it to the stealers. Note I am not mechanically minded at all bar a few basic things so go easy..

Thanks so much. Hope I've made sense/sorry for essay-length post etc..

[Mr2Mike]

A snapped exhaust camshaft is a common fault on this engine, caused by the camshaft bearing cap bolts loosening.

Was a compression test performed on the engine after the camshaft replacement? It's quite possible for valves to get bent when the camshaft snaps.

[WoodsterT]

They did when they replaced the coil pack, so I'm presuming they did again when they replaced the camshaft. When I took it back to them last week to try and diagnose this lumpy idle issue they said they did some "live tests" and didn't find anything abnormal; if 'live tests' means anything? They also mentioned something about how they checked the throttle body and that was behaving as it should.

Must be honest it all happened rather quickly I didn't really ask too many details, I was just glad the misfire was fixed at the time!

[Locknut]

The timing of the new camshaft could be set wrong, maybe just one tooth out. I also agree there is a possibility of valve damage.