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Idle surges in neutral going over 30 mph

1K views 6 replies 5 participants last post by  imps 
#1 ·
Hello everyone! So strange problem started up. My mustang would surge between 1200-2000 rpm when coasting above around 30mph in neutral and the check engine light came on for the IAC. I replaced it with a motorcraft one and now the light is off but it still surges between 1200-1500. The car runs and idles flawlessly besides that. Could it be a bad TPS as well?
 
#7 ·
I once asked EFI expert Probst (SAE) what does the PCM do when car is coasting at speed, throttle closed? Shut off injectors? NO! feeds minute amount of fuel to them. I would think the same thing is true if transmission is in neutral, though the fuel amount likely is less.
 
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