Idle Speed Control Valve - Faults

blackant · Postby **blackant** » Sat Nov 26, 2011 12:19 pm

2nd time this issue has occurred.
Get in car, start, no power windows, turn off, on, windows are back. Now the idle is 'off'. You drive along and as you break for the lights the revs hold at 1700 before dropping to tickover. As you sit there, they will suddenly go up, then drop down.
Replaced the Throttle body/ISCV unit last year after this happened and has been fine till now.
So, I detached the lead to the ISCV unit and turned the idle screw till the revs sat as per normal.
The car runs normally, although the idle is not as smooth, the revs are consistent, it just doesn't have a smoothness about it on idle.
There seems to be no difference on the road at speed.

What is the downside of running the car without the ISCV connected?

93_Clubman · Postby **93_Clubman** » Sat Nov 26, 2011 1:23 pm

When you replaced the TB did you clean it prior to installation? If not, perhaps worth a try, just be careful with what you use as the brown coating of sealant around the inside of the TB bore at the throttle butterfly can be damaged, which will affect idle.

de Bounce · Postby **de Bounce** » Sat Nov 26, 2011 1:33 pm

The issue is the idle won't compensate for any additional loads on the engine.
Things like lights (alternator load), power steer, aircon.
When you set the base idle higher to compensate for the load then you will waste fuel when the load is not present.

IMHO you would need to waste a heap of fuel to pay for an ISCV/IAC.

blackant · Postby **blackant** » Tue Nov 29, 2011 10:50 pm

thanks, idle under load doesn't seem to be an issue either, in fact other than minimal vibration felt through the gearstick on cold idle, the car runs as well as ever! what concerns me is why that is so, for if the ISCV can be bypasssed so easily why doesn't everyone do it? and more importantly, is it likely to be in the winter when issues arise from starting on cold mornings?