Idle problem after air filter change

[andyleep]

I have changed my Williams 2 airbox back to standard after having an induction kit on her. It idled fine before, but now runs anywhere from about 800 - 1400 rpm randomly. It'll pick up, shoot up to 1400 then drop down to 800, nearly cut-out and just constantly hunts between the 2. Ideas?

[Wobba]

Check wiring to the ISCV (three wires, must not short out on each other). Clean ISCV as well.

[andyleep]

Wobba, I see in an old post you've mentioned a white connector on the drivers side of the inlet manifold and if you remove it and start the car something about the ecu default values? Will this reset the values?

[Wobba]

No, if there is no input from that sensor (air temp I think?) it defaults to a value around 21 degree or something. You can reset some variables in the ECU by disconnecting the battery for a period of a few hours, or so legend would have us believe...

[andyleep]

Thanks Wob, I have a steady idle now. Cleaned iscv, fitted a new breather, cleaned tps and doctored the slightly broken wiring. All is good, except idling is at a constant 1200. So looking to adjust the tps in the morning!

[Wobba]

I think adjusting stuff like that may only mask other problems.

Try everything else first, like earthing points and very thorough air leak testing.

[Wobba]

Oh, and while I remember, try running the car as normal to operating temperature, then unplug the coolant temp sensor connector from the white sensor in the thermostat housing. Leave it a moment and go check the revs. Plug back in. Replace sensor if the car idles normally with it unplugged.

[andyleep]

Thanks for the info Wobba. After several checks everything seemed fine but was still idling high so I adjusted the tps and I now have a perfect idle at 900rpm. Happy days! But don't panic, I didn't touch any hidden adjustment screws, just rocked the tps back and forward until it seemed good and tightened the bolts. I knew the holes were elongated for a reason!