High idle won't go down

[Bitsyncmaster]

When you had this issue, did turning the AC on bring the rpm back down to normal? If so, what do the deceleration valve springs have to do with the AC compressor? Any ideas on how to troubleshoot?

TIA!

I don't recall. But any additional engine load would reduce idle RPM if your idle motor is already all the way closed.

[Ron]

When you had this issue, did turning the AC on bring the rpm back down to normal? If so, what do the deceleration valve springs have to do with the AC compressor? Any ideas on how to troubleshoot?

TIA!

The deceleration springs are supposed to be closed at idle. If the springs are too weak or the valves are bad, extra air is allowed in. The system will increase the fuel to maintain the air-fuel ratio. If the ISM can not compensate for the extra air, you are left with a high RPM.

Remove the W pipe and inspect the valves and springs. The spring's coils should be uniform...

Left bad. Right, probably weak:
Bad-Good Spring.jpg

Both bad:
Bad Springs.jpg