Code 35 will set when the closed throttle engine speed is 75 rpm above or below the correct idle speed for 45 seconds. Following are nominal warm engine idle speeds:
| Neutral | 900 +/- 75 |
| Drive | 800 +/- 75 |
| Neutral | 900 +/- 75 |
| 1000 +/- 75 |
Continue with test even if engine will not idle. If idle is too low, the scantool will display 80 or more counts or steps. If idle is high, it will display "0" steps. 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.
When the engine is stopped, the IAC valve is retracted (more air) to a fixed "Park" position for increased air flow during the next engine start. A scantool will display 95 or more counts.
A slow unstable idle may be caused by a system problem that cannot be corrected by the IAC. The scantool IAC counts will be above 60 counts if too low and "0" counts if too high
If idle is too high, stop engine. Ignition on. Ground diagnostic terminal. Wait a few seconds for the IAC to seat, then disconnect IAC. Start engine. If idle speed is above 800 +/- 50 rpm, locate and correct vacuum leak.
Idle speed may be too high or too low. Engine speed may vary up and down and disconnecting IAC does not help. This may set Code 44.
Scantool and/or voltmeter will read an oxygen sensor output less than 300mV (0.3V). Check for low regulated fuel pressure or water in fuel. A lean exhaust with an oxygen sensor output fixed above 800 mV (0.8V) will be a contaminated sensor, usually silicone. This may also set a Code 45.
Idle speed too low. The scantool counts usually above 80 IAC steps. System obviously rich and may exhibit black smoke exhaust.
Scantool and/or voltmeter will read an oxygen sensor signal fixed above 800 mV (0.8V). Check high fuel pressure or leaking/sticking injector.
Ignition on, engine stopped. Compare MAP sensor signal voltage with a known good vehicle with the same sensor. Voltage should be the same, +/- 400 mV (0.4V). Also, disconnect MAP sensor electrical connector. If idle improves, substitute a known good sensor and recheck.
Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging the bore.
See Service Manual Diagnostic Chart C-10.
Engine idling at normal operating temperature. Note RPM in Park or Neutral. Turn ignition off for 10 seconds. Start engine and immediately note RPM.