2007 astra vxr running very rich and has a misfire on idle p0170


Hi scotty got a 2007 astra vxr and it has misfire on idle, running very rich and very high vacuum on idle

the car is driveable and has awful fuel milage when ever i go anywhere near the throttle,high vacuum at idle and when at idle has a misfire will post a video soon the only code that shows up is a p0170 fuel trim manlfunction.

should mention that short and long fuel trims show -25 while cruising (usual to save fuel) but it shows up on idle and before i changed out my fuel pressure regulator due to a vacuum leak it was also staying like that at wide open throttle.

spark plugs are all carboned up as well as the o2 sensors when the code is not present after driving a while with the code on the spark plugs and o2 sensors would then start to show the typical tan colour.

the car when i bought it had:
forge recirc valve

forge actuator

tx autosport front mount intercooler kit

first cat decat (looked up the issue regarding these cars to see if that was the issue
these cars can apparently handle it on the stock tune and map here is a chat about it on the astra forums https://www.astraownersnetwork.co.uk/threads/would-the-decat-cause-this-problem.144255/)


i have tried several things to try and fix the issue including

new coil and plugs (ngk platnums PFR6T-G) stock ones by holden

new rear o2 sensor

new fuel pressure regulator (actually made a difference fuel trims no longer read -25 ON boost)

new one way pcv valve (found out it was no longer a one way valve)

changed mass air flow sensor both show same issue

also changed the front o2 sensor with a spare o2 sensor i had when i changed the 2nd one no difference

i should also note that the code pends for quite a while it only throws the check engine light after 2 drive cycles usually. but it still only shows that one code.

i already asked my local dyno centre they say they will not tune it untill i fix this issue i originally thought that a remap might fix this.

the only thing i have not checked is the intake manifold and the gasket as this is my daily and looks to be a huge job.

here is a link to my mega of the car boosting and idling

any help would be appreciated.

regards jesse