I have a 1990 Tracker. When cold it idles very high, 2300 RPM, then goes to a surging idle as it warms up< 1400 to 2000RPM, then after it is warm it idles nicely. How do I reduce the idle when cold and get rid of the surging

Thread: 6.0 V12 XJS High RPM When Warm - Jaguar Forum.co.uk

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Mar 3, 2013 - I recently bought a 1993 6.0 V12 XJS and when it is started from cold it runs ... to 1300 RPM so it wants to surge forward when braking which is strange. ...Classics · XJS 3.6,4.0,5.3 & 6.0; 6.0 V12 XJS High RPM When Warm ... You might want to adjust the aux (extra) air valve to bring the idle speed down.

High idle warm may indicate bad coolant temp sensor.

I've seen from 500 to 1500 RPM in all the manuals I've been through, depending on the year and application (truck/car). In personal experience, 650-800 RPM is acceptable warm operation range. This will also depend on elevation. Will go up to 1200-1500 RPM for cold starting. I live at about 2000ft and my '86 Pickup 22RE idles at 725-750 like a top after about a 3-4 min warm up @ 1250 RPM if it's cold (<45ish).

This is normally the way it is suppose to work. You need to have the RPM measured for High RPM and duration. What you are describing is how an electronic choke is suppose to work.

The errors would be how high the RPM goes and for how long it lasts. When cold the RPM, fuel mix and timing are changed to give a rich fuel mix. As the O2 sensors warm(Could be defective) they signal the engine to lean up. The water thermostat also has something to do changing the engine to a lean running slow condition.

If obtaining heat from your heater seems to take Forever, the thermostat could be weak. This would coincide with the engine continuing at a high RPM longer because it is not warming up.

should be in the 750-1000 range, just an adjustment on the idle probably

The long warm up suggests the thermostat has failed and is stuck open. The hard cold start is commonly caused by a faulty coolant temp sensor or the wiring connector on it. The idle surging can often be fixed by disassembling the throttle body and cleaning out the carbon build up. Be aware that the throttle body idle control box also has some internal gears that strip, also causing surge.

Sounds like a bad IAC (idle air control valve/sensor) that controls your idle when going from throttle to idle. If bad your idle will act crazy and can cause stalls easily. Pretty sure that's it.

Seems like an idle speed control to me.

sounds like the idle air control motor is sticking , not sure what engine you have 3.4 litre ?? also you can ck the throttle plate right on top where the throttle cable bracket assembly part of that bracket holds down a vaccum line that has a rubber gromnet that after time leaks causing idle surge , hope this helps

Problem might be the air control valve, it's located at the right side rear of intake manifold and has a hose going to the air intake duct from the air cleaner, as a test you might try pinching off that hose when the idle is a problem.