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Engine is a V8 3.5 block with a 3.9 top end and 14 CUX. Stepper motor has less than 350 miles on it. 

On start up, gets an immediate surge to @ 1500 rpm, then drops down in three "steps" to steady idle at 700 rpm. Takes a few seconds. Idles fine. When driving, it wants to stay in high revs as I downshift, such that after letting off throttle and rolling up to a traffic light, it will remain at 1500 - 1700 revs until braking starts to cause a stall, or after what seems an unduly long amount of time, it will drop to idle.

Checked throttle cable and assembly - no sticking and drops cleanly to rest.

So, thoughts?  Vacuum leak?

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Have you set base idle speed?

Also, this can happen when MAF is unplugged/dead.

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Think a reset?  Gunge on the MAF?

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Will reset ce soir and report back.

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Posted (edited)

Seems better 😎

Thanks for the advice.

Edited by RPR

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Isn't this (sometimes) something to do with the speedo signal to the ECU to stop it stalling as you roll up to the traffic lights?

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Yes, can also be that!

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Doubtful. The speedo hasn't been connected to anything for at least 12 years...

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The ecu needs the signal to know when you are coming to a halt. :)

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On 6/26/2019 at 6:58 AM, Bowie69 said:

The ecu needs the signal to know when you are coming to a halt. :)

Should it be connected? Never known a speedo signal is needed on the 14CUX?  🤔

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Some get away without, others find a huge improvement, go figure.

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