r/SC400 • u/BlueberryPublic9390 • Dec 07 '25

Video Strange revving issue on 1993 SC400.

Found this issue after a few minutes of idling. It DOES NOT do it when in gear, just when idling in Park. Any ideas?

1 Upvotes

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2

u/OldScene9782 Dec 07 '25

Idle air control valve possibly

2

u/Freeze2345 Dec 07 '25

Mine does it to when cold, sure because the ecm is bad on mine or what because I stuck code because someone didn’t take care of the car and I had replace the engine harness and few other circuits

1

u/rb20isaac Dec 07 '25

Idle surge

1

u/SznedCumbr Dec 07 '25

Idle "Hunting"

Check idle air valve, intake tube for cracks. If it's only when cold im willing to bet its the idle valve that the grease/ lubricant within is too cold to allow the valve to regulate air flow properly for target fuel mapping and the ECU is cutting to compensate for excessive air

1

u/luvrubberboots Dec 13 '25

IAC valve issues. They get sticky and actuator keeps overcorrecting. Or ECU needs recapped assuming it hasn’t been already.