IAC Fault Code and terrible Idle

[TVRCHIM400]

Hi All, hopefully the final issue to sort on the Chim (for now). The idle especially when cold is dreadful even to the point of stalling. It is better when it warm and does tick over at 950 to 975 quite happily. Performance when running is decent with good pick up and throttle response.

I have checked fault codes with rover gauge and it give me a code 48 relating to the idle control valve. Ok easy enough, I ve replaced the stepper motor and I know it has power and the ECU is communicating with it as I can manually open and close the valve using the rover gauge software. Its a good quality stepper motor purchased from RaceTech. So the question is what's the next step, has anyone had similar issues

Thanks all

[Belle427]

Never assume the new item is quality, there are some differences.
Why did you remove the old one?

[blaze_away]

Has it ever idled properly, or is that why you changed the stepper ?

If that was the case then first thing to look at is do you have any vacuum leaks. To do that properly you will need to do a test with a smoke machine. I had similar issues and could never get a decent idle with any stepper motor (I had 4 to chose from)

I finally found 3 vacuum air leaks, valley gasket, TPS spindle and heater pipes under the plenum. I fixed all those and now idle is perfect and 3 of the steppers were good, the 4th was a bit sluggish to respond. I was able to finely adjust the idle by the correct adjustment of the base idle screw on the plenum, which before I was not able to do.

[TVRCHIM400]

Thanks for the responses guys, yes I did change the stepper due to poor idle, your right it still could be a faulty unit I ve replaced it with but like I say I can move the steeper manually so hopefully this would rule out a poor unit.

I think I will get it booked in to a local tuning company for the suggested smoke test

[blaze_away]

I have a spare stepper that operates as normal by rovergauge commands for in/out BUT it gives me awful idling, very high revs on cold engine start up and frequent hi revving at junctions.

So even though RG manual operations appear good it could still be bad, where are you based ? If near I could test you unit on mine, I am nr Rugby