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My '86 c4 refuses to idle less than 2000 rpm. I have replaced the:
-IAC valve
-TPS
-vacuum system
-vac booster (thing the brake master cylinder bolts on)
I have also played around with the throttle adjustment screw, which had little effect. The coolant and 02 sensors look in decent shape so I don't think that's the issue. The only thing I can think of that I'm missing is the air switching valve, and the fuel pressure release cap (off the fuel rails, passenger side). Also should be noted that the car will start right up, and runs smooth, no fluctuations or dips in rpm. It will, however, steadily creep upwards but resets to 2000 when I tap the gas.
My question is could the cap being missing cause such high idle? I would think the cap being off would lead to low fuel pressure causing low idle, cuz not enough fuel? Any experience someone could throw my way would be very helpful as I have tried everything I found online, and am pretty lost at this point.
fuel pressure release cap pictured mid frame (not off my car just the internet)
Idle issue
