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[alex44]

2.2 petrol2013
The symtems are as follows, missfire on start up and also smell of petrol. running ok when driven hard the "miss" seems to clear and the firing is normal until desired cruising speed is reached them as the throttle is backed off the "miss" returns. No indicator lights are come on so do not think it’s an electrical problem.
I have fitted new plugs, air filter, petrol filter I have cleaned the throttle box and this solves the problem for 1oo miles or so but then the problem returns. Ideas?

[Nick W]

On a 2.2?


Cam sensor. Buy a new one, over the counter at your local Vauxhall dealer, and see if that cures it.

[flyer 0712]

Yep as already said..cam shaft sensor....I have had around 12 omegas and had that trouble with the majority of them...dont forget...buy genuine only..

[SIR Philbutt]

 Do a vacuum leak test around the inlet, servo and EGR, also consider the MAF before splashing out on a cam sensor, that is the least likely to be the problem
HTH Phil

[plym ian]

Possibly coil pack. Sounds like the symptoms i had with mine

[powerslinky]

Do a vacuum leak test around the inlet, servo and EGR, also consider the MAF before splashing out on a cam sensor, that is the least likely to be the problem
HTH Phil

Not knowing too much about 4 pots . . .but can't the OP unplug the MAF  as a test & run on default . . . before replacing it ?

Also if coil pack was causing miss fire  . . wouldn't that give codes ?

My money is on cam sensor  . . . seems by far the most common fault causer on 4 pots reported on Oof over the years.

And mostly without a code showing 

[SIR Philbutt]

Do a vacuum leak test around the inlet, servo and EGR, also consider the MAF before splashing out on a cam sensor, that is the least likely to be the problem
HTH Phil

Not knowing too much about 4 pots . . .but can't the OP unplug the MAF  as a test & run on default . . . before replacing it ?

Also if coil pack was causing miss fire  . . wouldn't that give codes ?

My money is on cam sensor  . . . seems by far the most common fault causer on 4 pots reported on Oof over the years.

And mostly without a code showing 

Al I would mostly agree with you

MAF unplug test is one way of considering if faulty although would cause a spanner light

Coil pack would give a misfire code but maybe not spanner. I get them sometimes when it stops to or runs out of LPG (spanner light stays on when the ignition lamp test end, should go out if no none critical codes stored)

Cam sensor is the common suggestion for most of the 4 pot problems but not the most common solution IME. I've had two desmonds over 10yrs and had not had to use my spare cam sensor I bought in the early days when it was suggested 

From the op's description of the problem it seems to be when throttle NOT in use the Miss fire occurs, throttle butterfly closed, Max vacuum min MAF. Any vac leak will confuse the EMS due to  lamba output, asks for more fuel and cause Mis fire and smell of petrol

Had experience of this, twice, one time was exhaust  manifold gasket leak where fumes fed back to EGR. Other time was EGR gasket where it bolts to the head.

Just thought, Alex44, also check the exhaust manifold itself has not cracked, remove heat shield normally shows on top