It seem this is an ongoing saga for a lot of people....
I've just purchased a very cheap, 2005 Facelift Signum 2.0t Z20NET engine (SAAB B207L) (Same is Vectra C Sri 2.0 Turbo), with 70k miles, nice clean car but has this idling issue.
When it fires up (Hot or cold) it's fairly mechanically quiet, but quite jerky for the first few seconds, like a misfire, but itís not.
It idles ok at the high speed on initial startup, then once it drops to the 750rpm idle, it's sometimes very rough, sometimes ok but only for a short time, then it's rough again. Stuttering and shaking the whole car body, it never stalls though and no fault light.
Have access to Snap-on Verus FCR and it has no fault codes stored. All real time data, eg temp, flow o2 look normal.
Washing out the mass meter, map sensor, air temp sensor with brake cleaner.
Cleaned and lubricated throttle butterfly, resealed the gasket.
WD40 all the electrical connectors
New fuel filter.
New exhaust manifold to head gasket (GM).
All exhaust gaskets and flexi are perfect.
Cleaned all electrical connectors in engine bay on all ecu's.
Checked for air leaks on manifold and associated pipe work.
It has recently had 2 new ignition coils, so I tried 2 more (No notable difference)
Changed ignition coil insulators down to the plugs (No difference)
Using Snap-on verus I operated all actuators and ignition coils and all worked faultless.
New auxiliary belt and tensioner pulley.
Disconnected battery for 30 minutes and cleared codes (Even although there were none), in the hope the adaptive ecu would relearn a new drive cycle...... no change
I'm now thinking chains/guides/tensioner, when I first got the car 2 weeks ago, I'd say there was a definite bit of chain noise, since then I've changed to oil to 5w30 GM own oil, and it's definitely quieter.
Going to take the cam cover, and front engine/lower chain cover off tomorrow for a look at these chains and stuff.
Trying to get hold of a pair of cam locks to check timing. Anyone managed without?
Also head of DMF's (Dual Mass Flywheel) causing this issue too though?
At my whitís end, any advice gratefully appreciated??