I have an Impreza WRX 1993 it is not accelerating as well as it should.

I had it put down for about two months because of a gearbox problem.

When I move off in 1st gear and accelerate to 4000 RPM the car starts to miss and spatter in all the gears. I thought that after driving for a while it would have cleared up, but it didn't. What happen is that the check engine light came on.

I went underneath the dash on the driver’s side and did my diagnostic. After checking the flashes it appeared to be trouble code (24)
(Idle air control solenoid valve)

1. I checked the input signal for ECM, (B44) No.2 - Body and (B44) No.1 - Body. It read 12.56 Volts for both No.2 and No.1, which No. 2 should read (8 Volts - 9 Volts) and No.1 (6 Volts - 7 Volts).

2. I checked the idle air control solenoid valve No. 1 - No. 2 and
No.2 - No. 3 that read 11.3 ohms, which No. 1 - No. 2 should read
8-11 ohms and No. 2 - No. 3 should read 8-11 ohms.

3. I checked the power supply to idle air control solenoid valve, which read 12.46 volt, which should read 10 volts.

What do you think is the problem?

I would greatly appreciate a response as soon as possible.