Toyota 1UZ-FE (non-VVTi) Idle Speed Control Solenoid Direct Fit Conversion Kit
Idle speed control is an important aspect of any engine management system. On engines with a mechanical cable-type throttle body, when the throttle is closed, a precisely controlled amount of air must be bypassed around the throttle butterfly to allow the engine to maintain a smooth and constant idle for various loads and engine temperatures. The ECU controls a type of valve to let this air into the intake manifold. There are two main types of idle control valves commonly fitted petrol engines with a mechanical throttle: stepper motors and solenoids.
The earlier, non-VVTi versions of the Toyota/Lexus 1UZ-FE 4.0L V8 engine (from approx 1989-1997) were fitted with a 6 wire idle control stepper motor on the front of the intake manifold. When retrofitting an aftermarket ECU to run one of these 1UZ engines, the factory-fitted stepper motor works perfectly well for many applications.
However, there are some disadvantages associated with idle control stepper motors, including:
- The ECU controlling the stepper motor requires more complex hardware and software to control it. Furthermore, more of the ECU’s available inputs and outputs are used up to control a stepper motor compared to a 2-wire or 3-wire solenoid.
- Idle stepper motors typically must be reset to a known position after the engine is turned off. This requires more complex wiring to allow the ECU and the stepper motor to stay powered briefly after the engine is turned off. As stepper motors are relatively slow moving, it can take a few seconds for it to reset prior to restarting the engine. This is especially relevant on jet boats as having to wait several seconds for the engine to restart can be undesirable or even disastrous.
- Stepper motors are generally more complicated to correctly wire and set up with aftermarket ECU’s. We typically find that our customers have more issues with getting stepper motors correctly set up and working when retrofitting an aftermarket ECU compared with setting up an idle solenoid such as the one included in this kit.
Due the increased complexity (and therefore, cost) of supporting stepper motor idle control, certain entry level aftermarket ECU’s only support the simpler idle solenoids. A common example of ECU’s that we encounter that fall into this category are the Link G4X AtomX and G4X MonsoonX ECU’s. While all other Link G4X wire-in ECU’s support stepper motor idle control, only idle speed control solenoids can be used with the AtomX and MonsoonX.
Therefore, NZEFI has developed this 1UZ-FE direct fit idle speed control solenoid conversion kit. The solenoid included in the kit bolts to the intake manifold using a CNC-machined aluminium adapter at the same location as the factory stepper motor. The kit includes:
- 2-wire idle speed control solenoid (a.k.a. ISC Valve, IAC Valve)
- 2-pin electrical connector with terminals and seals
- Solenoid gasket
- CNC-machined aluminium adapter
- 20mm barb fitting for intake hose
- Mounting hardware
Note that this product is not applicable to the later VVTi version of the 1UZ-FE engine as it is fitted with an electronic ‘drive-by-wire’ throttle (E-throttle), which is also responsible for idle control.
Recommended signal frequency = 120Hz
Solenoid valve is to be oriented so that the port furthest from connector is connected to the intake (vacuum) side