The next thing I wanted to check was the idle speed control. This is a fairly complicated setup in the Rover engine, using a stepper motor and something called the Input Air Control (IAC). It basically operates in the same way as we used to use a choke, but it is all automatically controlled by the Electronic Control Unit (ECU). Also known as the Engine Control Unit.
She started idling at 1400rpm then gradually started to drop, stabilising at 950rpm once she warmed up (You can see from the picture I blipped the throttle a bit at the 6.5 min point). The Rover T16 engine is supposed to idle at 850 rpm and although I have previously used software to drop the idle to that figure she always reverts back to 950 rpm. Originally the ECU was modified to remove the immobiliser function and I suspect that the default idle speed was upped a bit. So I’m happy with that. You can see from the screenshot that it gradually decreased then at the 9.5 min point there was a distinct step when she dropped from 1200rpm to 950rpm. I assume that is how it is supposed to work as the digital equivalent of the auto choke drops out.
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