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2006 Lincoln Town Car fast 30 second fast idle

We have a 2006 Lincoln Town Car with the 4.6 L engine. The car just had new spark plugs, PCV valve, change radiator fluid, transmission serviced, and some other minor work by a service garage. Car ran OK before the work. Now, with a cold start, the car runs at 2000 rpm for 15 to 20 seconds and then drops down to 1500 rpm for 15 seconds and then down to around 700, normal idle. With a warm start it runs at 1500 rpm for 15 seconds and then drops down to the 700 range. I took the car to another garage and they recommended fuel injector service and throttle body linkage adjustment. This did not solve the problem either. Any ideas.

Did any of the “some other minor work” include messing with the MAF/IAT sensor(s)?

I really wonder how they adjusted the “throttle body linkage” on this year car? I thought that the 06s were ETC…

I do know that my car a 2008 Mazda 6i that has the same cold start procedure which is “normal operation” it runs at 2000rpm for about 30 seconds, then down to 1200rpm for another 30 and finally resting at 750rpm when warm. I believe this is your idle air control acting normal as the weather gets cooler in the morning.

The one thing that sticks out that may be causing the problem is the coolant system service. If there’s air trapped in the cooling system, and it comes in contact with coolant temperature sensor for the computer, the sensor won’t read the proper coolant temperature. This can then cause the engine to go to fast idle because the signal from the coolant temp sensor is sending false information to the computer causing the fast idle.

Take the vehicle back, and ask that they purge the cooling system of any air that might have been trapped.