Does all the air used by the engine on idle come through the ISV? Mine developed a fault where it wouldnt idle without the throttle slightly open. I found the wiring at the back of the head had partially melted and had shorted out killing my ISV. I have changed it all but still can't get it to idle. If I take the ISV out it will "idle" at 1100-1200rpm.
I have replaced fuse 15 which had blown, and have also replaced the damaged wiring loom, coil, plugs, leads, and ISV from a donner running car. I have also checked all hoses to the manifold for leaks. It seems the engine is being starved of air, as it won't run unless the butterfly is open or the USB is completely removed. The ISV I have fitted hums when the ignition is on and the wiring to it has about 11.5volts.
next step is get diagnostics plugged in. also make sure the idle switch clicks when throttle is cosded and wiring from it to ecu is good, as well as the tps wiring. did you replace the isv? if so try the original. mine was very picky about this, I tried 3 different ISV before I found one my ecu was happy with fuse 15 was probably popped when the breather heater wiring shorted out behind the inlet. since we dont have the heater on UK mk2s you can remove it from the loom completly, its the 2 pin plug on the black plastic pipe with black and brown, the brown goes straight to the head so unbolt and bin, the black wire is tapped into the ignition live for the isv and ecu so chase it to the wire joint. remove tape, cut the heater wire off then replace the tape.
