IASC fault
 

My '96 Legacy GTB running a ESL board has developed an IASC fault ever since I fitted a 6 speed DCCD box.

When coasting for a prolonged period of time the check engine light comes up (I have checked codes and the IASC valve is the culprit). If I slow down to below about 30mph and press the clutch to allow the engine to idle the light often goes out and the car behaves perfectly. While the light is on the car drives ok gently but like a pig when driven hard. I have swapped the valve for my spare which I know works fine and the fault is the same so I am ruling out the valve as the problem.

Two other theorys I have are that the loom may be damaged (some of the strands in one wire broken) or the ECU is thinking the car is in a different gear due to the 5 to 6 speed swap (old 5 speed was a 4.44 ratio and 6 speed is a 3.90) and this is playing havoc with the mapping parameters.

I will be grateful if anyone can put my mind at rest or explain more about my ECU theory primarily, but all help and other theorys welcome.

Cheers, Guy

Might be worth checking the NPS is working the correct way compared to the 5 speed one.

Good shout - thank you

So a couple of weeks ago I tested the neutral position switch and discovered that it was dead. Last week it was replaced but the problem was still there......however easier to reset.

Yesterday I went to see the software programmer from ESL to do some data logging which was good to learn more about the idle control system (which is quite extensive!) but ESL could not nail down what the fault was and wanted to log another standard car with a five speed box. I went from ESL to Martin Hall (hallie on UKLegacy.com) who worked out that the NPS is positive when the car is in neutral in a five speed box but the opposite way round with the 6 speed DCCD! Kudos must go to merlin24 for his guess and thanks to ESL and Martin Hall.
Plan now is to fit a relay to make the switch behave like a five speed.