VVC very high CO on MOT

Originally posted this in the MGF section because I figured more people would own a MEMS2J VVC there than here, but didn't get much feedback other than change the lambda.

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Just stuck my VVC in for an MOT and its failed on a very high CO, around 7%. Its a MEMS2J model, with the coilpack on the block, not on the head.

___ Actual ___ Limit

CO 6.94% 3.5% MAX FAIL

HC 307ppm 1200 MAX PASS



IDLE SPEED: PASS

SMOKE LEVEL: PASS



If you notice the emissions levels are a lot easier to pass, this is because the engine is in a 1992 metro. Was originally out of a 1999 R200 Vi though, and one of the fails before I took the engine out was high emissions at similar levels.



I'm just trying to work out what to start replacing first.



Things that have already been done:

I put a new lambda sensor (think it was NTK) on it before it was laid up for a year. Can these things corrode as the downpipe was left off for most of that time?

Magnecor leads are fairly new

New spark plugs last week



I stuck my multimeter on the air temp sensor and it read 600ohms, i'm guessing if it failed it'd be open circuit.

The cooling fan kicks in when it gets hot, and follows a resistance gradient that I found on some site so that seems fine.

I've checked the throttle pot and that seems to have a linear resistance gradient across its travel.



Checked the timing and thats spot on.



I'm thinking that the cat alone won't cause a reading that high, it passed an MOT with that cat about 1000 miles ago, although it has been left disconnected outside for about a year.



The idle sometimes seems to sit slightly higher than normal, and a blip of the throttle brings it down again. It isn't the throttle body sticking, it seems to be throttle position sensor related. Could that cause high CO?



Probing the O2 sensor, once warm it just sits at 0.9-0.95v, which means its running (very) rich. I would expect the ECU to be trying to lean this off with that signal but it doesn't appear to be happening. Basically doesn't appear to be going into closed loop.



What sensors could cause this. I know if the cam sensor goes it goes into grouped fuelling instead of sequential. Would this also stop it going into closed loop running? Can be a pain to start sometimes but it is much improved when I disconnect the fuel cut off switch until its running, then reconnect. Leaky injector maybe?



Any help greatly appreciated, need to get it MOT'd before the end of the month as it needs to be off my drive by the 30th. Will be getting weighed in otherwise as I need to get my campervan off road to repair it.

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