High idle problems it happens after a while of driving and coming to a stop say 30 minutes. When I'm sitting parked it's almost like I'm pressing the gas pedal up to 3k rpm and it doesn't bounce it stays there. I had to shut the engine off and pull the battery cable to get it to stop being at 3k rpms so I could get it out of park and drive. Seemed fine after that but having to pull the battery cable to solve the issue is odd.

I replaced the Idle control valve, front O2 sensor, and Vapor Canister Vent Valve / Solenoid.

It seems like the engine is really hot as well, the fans kick on and the radiator is working fine. I guess it makes sense if it's not moving and it's high rpms.

I checked the throttle cables they look okay.

No fault codes.

I heard it might be the computer or perhaps the throttle position sensor?

 

I use google AI to get some answers sometimes now.

1. Throttle Position Sensor (TPS): The TPS could indeed be a culprit. If it's providing incorrect readings to the ECU, it might cause the engine to idle incorrectly. You can test the TPS with a multimeter to ensure it's operating within the correct voltage range.
   
2. Throttle Body and Linkage: Even though the cables look fine, the throttle body itself might need cleaning. Carbon buildup can cause the throttle plate to stick, which could result in a high idle.
   
3. Vacuum Leaks: A vacuum leak can cause a high idle. Check all hoses connected to the intake manifold and listen for any hissing sounds when the engine is running.
   
4. Coolant Temperature Sensor: If the engine is getting excessively hot, the coolant temperature sensor might be malfunctioning, causing the ECU to adjust the idle speed incorrectly.
   
5. ECU (Engine Control Unit): Although less common, the ECU could be faulty or need reprogramming. If it’s sending incorrect signals, this could lead to high idle issues.
   
6. Intake Air Control Valve (IACV): Even though you've replaced the idle control valve, the IACV can sometimes be affected by wiring issues or connection problems. Ensure that the connections are secure and there are no breaks in the wiring.
   

To diagnose the problem more accurately, consider the following steps:

1. Check TPS: Use a multimeter to check the voltage readings from the TPS at different throttle positions. Ensure it smoothly transitions from idle to wide-open throttle.
   
2. Inspect for Vacuum Leaks: Perform a smoke test or use a propane torch (unlit) around the intake manifold and hoses to see if the idle changes, indicating a leak.
   
3. Coolant Temperature Sensor: Check the resistance of the sensor at different temperatures to see if it matches the specifications in your service manual.
   
4. Scan Data: Even though there are no fault codes, using an OBD-II scanner to look at live data might reveal anomalies in sensor readings.
   

 

Just want to be clear. You drive for about 30 minutes and as soon as you come to a stop and put it in park the idle shoots up to 3k? Or are you idling the car for 30 minutes then it happens? and it happens every time?
Nothing wrong with an engine being hot specially if you are idling for such a long time or high rpm.

 

After driving for 30 minutes and yes after I come to a stop or slow coast the idle shoots up and settles around 3k it doesn't t jump around. Yes it's been happening every time. I do think it's odd that removing the battery terminals stops the high rpms otherwise it will resume the 3k rpm after turning the engine back on. Is there any reason why it would reset when I pull the terminal connector?

[​​​​QUOTE=Jon M;16939763] Just want to be clear. You drive for about 30 minutes and as soon as you come to a stop and put it in park the idle shoots up to 3k? Or are you idling the car for 30 minutes then it happens? and it happens every time?
Nothing wrong with an engine being hot specially if you are idling for such a long time or high rpm. [/QUOTE]

 

The reason it resets after pulling the battery cable is that resets all the electronics. The idle is being commanded by the electronics. My guess is it is one of two things. The Idle air controller (IACV) or the ECM that is controlling the IACV. I know you said you replaced the IACV but what when and what brand did you use? This is one of those items that these cars really want the OEM, cheap knockoffs won't work correctly. I don't mean to sound insulting but have you checked to make sure the electrical plug to the unit is still plugged in? If it is all connected you can try driving and then when it idles high disconnect the IACV and see if it changes. I would also pull the IACV and see if it is stuck.

 

I'd refer to the service manual idle control troubleshooting on page 11-148. When the car is warmed up, and at idle, what happens when you disconnect the IACV connector?

 

Used to have this issue on my CL when it was an automatic. Except mine would go up & down in the RPMs once I put it into park. Stopped after I converted it to a 6 speed manual.

Guess the fix is to just manual swap your TL

But it's probably the IACV. I usually pull them off, and spray some brake cleaner in the ports and scrub it, dump it out, then spray some silicone lubricant. I also take a car battery and wires, and touch two of the pins until it moves/flutters to help get the cleaner and lubricant into all the moving parts. This usually works for me, but sometimes, they're just old and tired and need to be replaced.