Hey guys,

I've got a problem that has got me stumped.

I cant manage to get the idle of my car to stay stable. No matter what I try it always rises up to 1400rpm once it is warm.

Background info:

Its an AU2 ute. Previously it had a T5 conversion and supercharged with a 2 bar map sensor off an XR6T and tuned with a flash tuner. It runs an auto ECU with an auto tune. The idle was fine.

I took the charger off and put the car back to standard and the idle was fine.

Preparing for an T56 conversion I ran the speedo off the ABS using jaycar correctors but left the VSS in the T5 gearbox. All I did was chop the wire at the back of the cluster and feed the jaycar output into the dash.

The idle was fine.

Now the car is turbo, the 2 bar map sensor is back in, it has a nizpro plenum and its running a J3 tune that was based on the flash tune, the T56 is in and the VSS has been removed and the idle is doing my head in. No matter what I adjust it will start at 800rpm then after a few days rises to 1400rpm. If I turn the car off and on the idle starts at 800 for a few seconds then rises.

Ive adjusted the base idle, reset the TPS to under .7v, replaced the ISC with a new one, fitted the restrictor trick for the trans select switch (I didnt need it before), I've adjusted the VE table and idle timing maps about 50 times, all with no result. Ive blocked off the ISC with a gasket with smaller holes, blocked the ISC off completely, all with no change once Ive driven it a few times.

Would unplugging the VSS have any affect on what the ECU does compared to just having the signal wire to the dash cut?

It outputs a 10v square wave usually but im guessing the reference voltage and ground wires are affecting something because they arent connected anymore. Is this possible?

Any other ideas?

New VSS made no difference.