This is rather long so be patient. If your Astra or Z18XE enigined vauxhall has these running problems then you may have cracked it and found the right solution - I had been searching for correct answer for ages .
My Astra developed what I can only describe as a hesitation when accelerating and a distinct lack of power. This went on for several months and then it got worse till about 2 weeks ago the engine fault light came on and gave a fault code 0170 fuel trim bank 1 malfunction.
Reading all the bloggs led me to believe it was the Air flow meter but my son who is a motor tech said it was Lambda 1. So I sent off for both - they were after market type - but nice and cheap.
The AFM came first so we fitted it - then we got a fault code for the AFM - that went straight back - We put the old one back in and it was the same as before and same code came up. This sort of led me to think that the AFM was not at fault. I changed the Lambda, Plugs and air filter and it got worse. I changed them all back but no change still very bad running. It started ok but was a pig till it was warm - no response to start with and then after 2 mins it stablised and it could be revved to 2200 rpm. If you pushed to full throttle then you could get it to slowly whiz up to oh at least 4000 rpm where it spluttered like a good un. It was not mis firing only felt like a lack of fuel. So I decided to replace fuel filter and strip down the injectors. Half way thro I wished I hadnt. You really need to remove move of the harness and electric loom to injectors and the fuel rail is a real pig to get back on. I used a ptfe based lube spray with lots of brut force. And guess what - still no change. Last resort was thinking of replacing ECU - got that from bloggs. But dont be too hasty. I spoke to guy on Ebay who programs and fits these and he was prepared to come out 85 miles to diagnose and fit a good second hand AFM and an ECU if required for the best prices I could find on Ebay. Well he came out tonight from Colchester and diagnosed with a tech2 and laptop and saw that the AFM was not functioning properly but it was functioning a bit. We changed it and hey pressto the car is back to normal. Didn't need the £200 ECU but I was more than happy to pay £60 for his AFM and his work. I would highly recommend this guy - Arpy on 07766222470 he really knows what he is doing. For all you people out there there is one really big moral to this read - don't buy after market units they really are rubbish compared to the real part. I just wished I had stuck with my original suspision of AFM.
Hope this helps - Steve