High Idle Issue, '87 300ZX Turbo

[enxss]

I am having an ongoing issue with the high idle on my '87 Turbo that I have been unable to correct. The issue occurs when the engine is cold and first started. According to the factory service manual the maximum high idle speed should be approximately 1,250 RPM. However, my engine is obtaining a high idle speed of close to 2,000 RPM.

In my attempts to correct this issue I have tested and/or replaced several components. They are:

Auxiliary Air Control Valve (AAC) - Replaced Air Regulator - Replaced EGR Control Solenoid - Replaced EGR Control Valve - Replaced Throttle Valve Switch - Replaced Exhaust Gas Sensor - Replaced Pressure Regulator Control Solenoid Valve - Tested, OK Air Flow Meter - Replaced AIV Control Solenoid Valve - Tested, OK Crank Angle Sensor - Not Tested, No Mistiming of Fuel Injectors AIV Unit - Tested, OK Cylinder Head Temperature Sensor - Replaced Pressure Regulator - Replaced Vehicle Speed Sensor - Not Tested, Speedometer Functions Properly Air Conditioner Switch - Not Tested, Idle Step-up Functions Properly Ignition Switch - Not Tested, Functions Properly

In addition to the above, I have performed a full tune-up including plugs, filters, PCV valve, cap, rotor, and wires. I have also thoroughly inspected the various vacuum lines for possible leaks (e.g. cracks). Furthermore, I have gone through the self test diagnosis steps on the ECU - all shows normal.

The only other symptom that I have noticed is that the engine does not immediately return to normal idle after it reaches operating temperature. For example, if the car is driven from one traffic light to the next the engine will initially idle at approximately 1,200 RPM when you first disengage the clutch to stop. After waiting at the light for a short period of time, say within 30 seconds, the engine will slowly drift down to a normal idle of approximately 700 RPM and remain there until the cycle repeats itself at the next traffic light. In all other respects the engine runs fine with turbo boost normal across all speed ranges.

At this point I am stumped. Can anyone offer any suggestions?

BTW, there is one Vacuum Control Valve illustrated on page EF & EC - 10 of the factory service manual that I am unable to locate on the engine. Does this valve actually exist as a stand alone component? Or is it perhaps an integral part of some other component?

[evildky]

check timing? extra advance can raise idle

check fro vac leaks?

check throttle pistion, the tb has an adjustable stop, however it should be completely closed as the Z31 uses an idel air controller to regulate air flwo at idle

[redw20s]

vac leak most likely

[manuelrys60]

HAVE YOU CHECKED YOUR F.IC.D I HAD THE SAME PROBLEM SEEM'S LIKE THE SOLONOID'S GET STUCK I REPLACED MINE AND PROBLEM SOLVED!!!