Hi all, I have a mk2 golf with a PB engine. The emissions have always been high, 4-5 % ish. The adjustment screw on the throttle body is adjusted to the limit, all the way to the top but it's still 3.5%. If I completely remove the screw it drops to 0.7%. If it's screwed right down it's 9 %. I am setting it up using the correct technique( hose blocked, blue sensor unplugged and revved over 3k 3 times). This is on a MOT emissions tester. The car drives and idles fine. Vacuum hoses renewed and air flow meter air bypass cleaned out. Any ideas it's driving me crazy!
Do you do much town driving? Is the throttle body clean? Is the air filter black? Put in some super unleaded, get it hot, go on a long run (by pass, motorway) to burn all the **** off. Always helps P.S That rubjonnys guide is good, i'm sure you'll sort it out.
There is a CO adjustment on the AFM using an allen key. Clockwise richens the mixture and anticlock leans it out. I would suggest to return the engine to a stable idle and adjust the CO via the AFM bypass. If it is still over 3.5% CO ( MOT CO limit for pre 92 vehicles) you may want to adjust the AFM spring.
Thanks for your help. I have set the car up using the tuning guide. I have had the car for six years and it's always had high emissions. I am setting the co at the air flow meter. Looking inside the afm it has an air bypass channel and the adjustment screw changes the amount of air through this. I have tried setting it up with the air filter removed to eliminate, no better though. I might be wrong but I don't think the afm flap moves at idle so cannot influence the readings. An oil change made no difference. Any other ideas? Cheers all.
Is it completely standard with no modifications? Nobody swapped injectors or higher fuel pressure regulator fitted to the fuel rail? Kjet pump maybe fitted by someone that did not know any better. Can you get a shot of a different working AFM and try that. It would not take too long to fit and see if that cure the issue.
I changed the blue temp sender a while ago and this made no difference. Setting the emissions with it plugged in or unplugged gives the same readings. Vacuum pipes are new and there's no air leaks. I work in the motor trade but it's the lack of info available for the fuel system that is making it hard to find the problem. I've read through all the previous posts for similar problems, it's a shame people don't do a final post to let others know what fixed their problem! Anyway, the car is standard. Drives and idles really well. It's must only be rich at idle. Does anyone know what influence the afm has at idle, I haven't got another to try. As I say if I completely remove the mixture screw from the afm it drops to 0.7% but this is just creating an air leak and thus weaking the air/fuel mixture. I appreciate all the help guys.
Sounds like you're heading in the right direction then. It would be worth checking the fuel pressure, if you've got gauges, but it's starting to point towards the AFM.
What the MK2 Haynes manual and the FAQ guide on here are trying to achieve, would be to set up the OE engine hardware within a designed control window. If this has little or no effect on controlling the engine then something may have drifted outside of normal limits. The AFM is very easy to tamper with and get wrong. Assuming the glue is still on the AFM slider, the AFM position on the resistor card and the idle switch on the throttle, tell the ECU to look up the idle spark and fueling tables. You can tweak the AFM position when the idle switch is activated with small adjustments rich or lean with the bypass or by repositioning the AFR return spring 2 knotches or so to have more tension (toward leans operation). Dizzy location will also help trim some of the HCs with slight increase in NOx if advanced. Best done with proper 3 way gas sniffer.
Thanks guys most helpful. It does seem to point to the afm. I did remove the top cover of the air filter housing so I could see the flap with the engine running. It was closed at idle so I wonder if the signal being sent from the afm control unit is incorrect. I'm gonna have to dig a bit deeper, more time and money I expect. Many thanks for all your help so far.
Cheers but i'm in Portsmouth. I'll do some electrical checks and open up my afm and check the wiper track for wear. There's quite a bit of info on the net about problems with these. Thanks though.
2e code 2.0 8v isv and afm both fit the digi MK2, chances are you'll find these in better condition. especially if you can find an automatic passat or vento, unlikely these have been ragged within an inch of their life. edit: i'm pretty sure at idle the afm arm should move a bit, but its been a long time since I looked at the insides of one
Have you checked the resistance of the AFM with a multimeter? There's a spec in the Haynes for the air intake sensor, and for the potentiometer.
Hi. I'll have another play at the weekend, can't risk breaking anything during the week as I won't be able to get to work . I think i'll have a look inside the afm and do some checks with a multimeter. Hopefully i'll find something. Fingers crossed. Cheers all.
does this not say it could be a problom with the wiring or connection if it makes no difference it might not be making a connection and running in setup mode constanly. maybe. i have a problom with mine that its set up fine, is fine around town but drinks if i drive above 3k on the motorway.
Hi. Sorry i've just seen you're reply. I had the air flow meter apart and cleaned up the track and connections, shifted the wiper slightly to a better part of the track. Checked the resistances and all are now in spec. Haven't had a chance to get it back on the emmissions tester yet. I reckon the wiring is o.k because with the blue temp sensor plugged in the car starts, with it unplugged it doesn't. Bit of a basic test I know but seems to prove the wiring is good. Seems to be running a bit better as well since fiddling about. Cheers.
