Re: Is it the idle stepper/TPS?
Is that code an indication of his car running too rich as the other symptoms would indicate?
Hangten I take it that you have checked it`s not something daft like a collapsed baffle / partially blocked exhaust or mis-timing when the cambelt was replaced?
I purchased a plastic top engined 146 recently that the previous owner and motor trader I bought it off just could not get running right. They had changed the crank, lambda & speed sensors, put in new plugs etc but it still ran lumpy, gutless and had a wavering tickover (800 to 3000 RPM). The trader's mechanic tried bypassing the MAF with a resistor which resulted in power being restored but a 2500 RPM tickover.
I put injection cleaner in the tank, replaced the MAF, cleaned out the throttle body with carb cleaner, oiled all associated moving parts, then did the stepper with switch cleaner/lubricant. This greatly improved things, no jerky response, fuel consumption up from 13! MPG to high 20s, however when decelerating from any speed where engine revs had gone above 3500 the tickover would still stick at 2500 RPM, needing a blip to 4000 to clear it and the exhaust still smelt rich.
I tried lubricating & re-routing the throttle cable which had worn through where it rubbed on the battery but that wasn't the culprit.
Being able to find no obvious code or fault that didn't point at something that had already been done/renewed I was almost resigned to lashing out on a new stepper but wondered whether maybe the ECU just thought that the engine was running too cold and was therefore over-fuelling it. So I changed the thermostat (£26 local motor factors) and now mine is running perfectly with all symptoms gone and I'm getting mid to high 30s MPG.
I still can't believe how sensitive the engine management system was to a relatively small variance in what it perceives as acceptable running temperature although to be fair the car warms up in a fraction of the time and under no circumstances deviates from 90 degrees now.
Mine had quite a bit of oil residue in the throttle body which I assume is what contaminated the MAF so I'm going to bung some Ametech in to hopefully reduce the heavy breathing as it supposedly greatly helps the bores/rings & valve seals.
Also I hope you had the MAF well away from the throttle body when using the WD40 and ran the engine for a while before re-fitting it as silicon is the best known contaminator/killer of MAFs.