This problem happened in around late April when we had the stay home advisory. When car is "cold" idle is fine, in park or waiting for traffic light. Once the car is driven for a while - "hot", idle speed goes up above 1300 rpm in Park position and a bit over 1000 rpm while waiting for traffic light.

Initially, I cleaned the IAC and the valve inside was moving freely when I shake the IAC. I also cleaned the throttle body too, not too much black deposit around the front and back side of the throttle body valve. Test drove the car after cleaning, same issue.

Then I got a new IAC from Volvo dealer and installed it. Still the same idle issue when car is "hot".

My car is 1995 NA wagon, what could be the problem here to cause the high idle in Park or waiting for traffic light ?

Thanks,

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, E-Code Lens, Alpine CD-Changer, AutoDim RearView Mirror

Hello Ho, it's been quite a while since you have posted.

You might want to check the engine temp sensor, next to the coolant thermostat. Just unplug it and check the resistance of the sensor. Warm engine is should read 150-300 0hms, or close to it. With the engine at 70F (cold) the resistance is much higher - 2800 0hms. A perpetual cold reading will introduce more gasoline to the cylinders.

Also check the linkage at the throttle end, make sure all of the ball joints get a little lithium grease. Your low idle speed when warm should be around 850 rpm.

Of course, there is always a threat of a bad vacuum line connection. Once the engine bay heats up, the older vacuum lines/elbows get soft. Check those around the air box and the one going to the air box thermostat that moves the flap for cold air Vs warmed air intake.

You might want to remove the warm air intake and make sure the air is coming from the cold intake.

Sorry you bought a new IAC, they get dirty but seldom fail.
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Keeping it running is better than buying new

Hi KlausC,

You are correct, I have not posted for a long while. Car is runnning fine so far except the tear and wear items: exhaust manifold flex elbow, power steering rack leakage, AC leakage issue. Those were out of my abiltiy to fix so I let Volvo garage (not dealer) to fix them. Actually, nowadays, Volvo garage is almost the same price as dealer !

Back to the issue, did you mean the coolant temperature sensor (engine temp sensor) ? If it is then it was replaced years ago. Can I unplug this sensor while the car is running to measure the resistance ?

I checked the throttle rod, it was fine, no binding. Since my car is NA, so it does not have too many vacuum tubes around the throttle body/IAC. I will double check them.

For the airbox thermostat, are you talking about the small metal cylinder with a pin at one end ? If that is the one then I have that replaced years ago too. So this thermostat should close the flap to stop the warm air from exhaust manifold and allow cool air coming from the front bumper (above the radiator) ? I could disconnect the aluminum tubing from the airbox to the exhaust manifold to see what happens when car is up to temperature.

Thanks,

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, E-Code Lens, Alpine CD-Changer, AutoDim RearView Mirror

A2-233 means there is unmetered air entering the intake. Usually a vacuum line, but it could also be an air leak around an injector or intake manifold gasket. Check the air tube from the filter to the throttle body for cracks - happens with age.

A1 is transmission faults.

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Keeping it running is better than buying new

Got it. I will check around the air intake tube.

Thanks,

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, E-Code Lens, Alpine CD-Changer, AutoDim RearView Mirror

I just checked DTC code and found one in A2: 233 (Idle Air Trim Exceeds Control Limits); A1 had no code (111). So any more suggestion to troubleshoot the issue ?

Thanks,

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, E-Code Lens, Alpine CD-Changer, AutoDim RearView Mirror