Another Idle Issue Except Backwards!

[mhyphenl 10 1 Cars]

I've been having this issue for a while, just rebuilt the engine and was hoping it would miraculously solve the issue.

 

Start the car and idles at around 1200. After about a minute, just as the revs start to think about starting to drop, the K light comes on and the revs climb to about 1500 over a few seconds. If I rev the engine the revs fall back to 1200 ish and the k light goes off. The revs then creep back up to 1500 ish and the k light comes back on. This stays the same apart from the lower revs value goes towards 900 ish and the higher to 1100 ish as the engine warms up (so the SAD is working!).

 

It has a new temp sensor and the lambda was new around 1200 miles ago, the AFM is a replacement but was second hand and I'm almost certain has been tampered with, I think this may be part of the problem / solution but I need to understand what's going on in the ECU's tiny mind to try and work out the solution. The only fault code is 52 (fuel mixture adjustment) now on Autodata the solution to this is to check everything!! I'm as sure as possible that there are no air leaks, I've even replaced the vapour recycling valve thingy as this is about the only purposeful introduction of unmetered air.

 

My thoughts are that for the first minute or so while the engine is very cold the ECU just runs on a pre-set output and the lambda is ignored, then after a certain time or temperature it kicks in, and starts to try and adjust. For some reason (rich or lean?) the revs are rising as a result of this adjustment but the ECU is putting the light on as it's not able to bring emissions into line, or the results aren't fitting into the acceptable range for a given set of values. What would cause a rise in revs? idle too rich so trying to adjust leaner or the other way round??

 

As mentioned the Temp sensor is new so unlikely to be to blame, I think the AFM has been tampered with as there is a mark on the sprung wheel in tippex and the lid was loose when I got it but I have no idea how to go about making adjustments or knowing whether it is in fact out. I think i know that a clockwise adjustment tightens the spring which closes the flap slightly which makes the ecu think there's less air entering so reduces the fuel and leans it up?? is that right?? I'm thinking it's too lean at startup and when the lambda kicks in it's giving the signal to add more fuel which is making the revs rise at tickover but which puts the figures out of range and puts the light on!? I'm not sure where the revving of the engine making the k light go off temporarily fits in?

 

I'm guessing I'm not going to get far without a gas analyser but is there anything I can try at home?

 

Hope I've not twisted antones melon too much with that post,suffice to say it's certainly twisting mine!!

 

All the best

Martin