DTC 35

Code 35 - Idle Air Control:

Wiring Diagram For Code 35 - Idle Air Control (IAC):

CODE 35 - IDLE AIR CONTROL (IAC)

Circuit Description:

Code 35 will set when the closed throttle engine speed is 50 RPM above or below the correct idle speed for 30 seconds. Following are nominal warm engine idle speeds:


AUTO MANUAL ALCL
Neutral 950 +/- 50 950 +/- 50 1000 +/- 50
Drive 725 +/- 50 1000 +/- 50





Test Description:

1. Continue with test, even if engine will not idle. If idle is too low, "Scan" will display 80 or more counts, or steps. If idle is high and a visual check of the idle air passage shows a seated valve, locate and correct a vacuum leak. If the idle is very high, usually above 1400 RPM and the IAC valve is not visible in the air passage, follow the left side of chart. Occasionally an erratic or unstable idle may occur. Engine speed may vary 200 RPM or more up and down. Disconnect IAC. If the condition is unchanged, the IAC is not at fault. There is a system problem. Proceed to paragraph three below.

2. When the engine was stopped, the IAC Valve retracted (more air) to a fixed "Park" position to provide increased air flow during the next engine start. A "Scan" will display 95 or more counts and the valve should not be visible in the idle air passage. Disconnecting the IAC will hold the valve in a retracted or open position and cause a closed throttle idle speed above 1500 RPM. A "Scan" will now display "0" counts because the ECM has tried to reduce the idle speed by extending the valve. The TAC is OK. The code 35 is likely a thermac or cruise control vacuum hose disconnect.

3. A slow unstable idle may be caused by a system problem that cannot be overcome by the IAC. If the IAC is visible in the air passage the chart should locate the problem. If the valve is not visible the IAC is probably OK. In both cases, the "Scan" counts will be above 60 counts.


^ System Too Lean (High Air/Fuel Ratio)
Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. May set CODE 44. "Scan" and/or Voltmeter will read an oxygen sensor output less than 300 MV (.3V). Check for low regulated fuel pressure, water in fuel, or lean injector. A lean exhaust with an oxygen sensor output fixed above 800 MV (.8 mv) will be a contaminated sensor, usually silicone. This may also set a CODE 45.

^ System Too Rich (Low Air/Fuel Ratio)
Idle speed too low. IAC valve not visible in idle air passage and "Scan" counts usually above 80. System obviously rich and may exhibit black smoke exhaust. "Scan" tool and/or Voltmeter will read an oxygen sensor signal fixed above 800 MV (.8V).

Check:

- High fuel pressure
- Leaking TBI injector O-rings or injector. Ignition on, engine stopped. Using a fused jumper, connect 12 volts to fuel pump "test" terminal to pressurize system. Visually check for fuel dripping into manifold.
- Rich injector

^ Throttle body - Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging the bore.
^ Additional checks, see Diagnosis By Symptoms - No Trouble Codes
^ Code 35 with A/C "on"; Check A/C compressor or relay diagnostic Chart C-1.