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MG TD TF 1500 - Engine Idle speed

I set my idle speed at 1000 rpm with the engine hot and a third party temperature gauge, that appears to be reasonably accurate, reading 180DegF. The temperature sender is located correctly prior to the thermostat. In cooler weather the Gage rarely shows a temperature higher than 180 when cruising. It is now hotting up here in Florida and the gauge regularly shows 190+ and may peak at 200+ standing at traffic signals. It takes several miles for the engine to hear soak running at 3,500 rpm. At 190+ the engine idle speed drops to as low as 750rpm and the engine runs rough. It requires slight throttle to return to smooth running idle at 1000rpm

After moving off from standing traffic with a temperature gage readings of 190+ and the rough idle, the engine pulls well and will accelerate up low hills. There is no Dieseling at shutoff.

At startup the idle settles at 1000 rpm when the choke is released. During this hotter weather the engine starts first pull of the starter with some choke.

Any thoughts why the idle speed drops as the engine heats up?

1955 mgtf 1500 9194
I Massey

Well hot air is less dense than cool air so your fuel air mixture is probably getting richer as the ambient air heats up. Thus reducing your idle speed.

TW Burchfield

This thread was discussed on 19/06/2016

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