I think that I am getting closer to root cause. Now, the problem is there everyday at the first time that I drive the car. At the end of a 15 minute trip, I stop the engine but do not turn off the ignition. The problem is still there. I then turn off the ignition and turn it back on - the problem is gone. It will stay gone for the rest of the day until the car sits for 4 - 6 hours.

Anytime the problem occurs, it will go away if I pull the plug that goes to the TPS on the engine.

Here is why I think I am closer. For the first trip in the morning, the problem is there. So I turn off the air conditioner, turn off the ignition, and then turn the ignition back on - the problem is gone.

So it appears that the on-board computer thinks that someone is slightly pushing the throttle. Turning off the air conditioner turns off the solenoid that slightly increases the throttle when the AC is on.

Perhaps I just need a slight adjustment of the AC throttle positioner.

 

no "A/C solenoid" the idle is controlled by the IAC valve. one thing you might try is removing the throttle body and cleaning it. a carboned up TB can keep the throttle valve from closing all the way resulting in your issue. you can also use the opportunity to adjust the throttle cable, they do stretch and can be adjusted.

 

There's no AC solenoid, but there should be software in the ECM that opens the IACV in "anticipation" of the AC. That's why the AC circuit goes through the ECM.

If the idle-control system simply reacted to the load, it wouldn't control as good as it does (or as it should when it's working). So maybe that signal from the AC isn't getting where it needs to be?

If you adjust your throttle cable, make sure it isn't too tight. The throttle must close, and the cable must go slack - just not excessively slack.

 

Thanks for the info. I did see where the AC throttle control goes to the IACV. The car only has 37,000 miles on it, so I think I can rule out a carboned up TPS. I am assuming that I would need to adjust the AC throttle cable as opposed to the normal throttle cable. Turning off the AC prior to turning on the ignition seems to work every time in allowing the park solenoid to work. I can look at the throttle control reading on my ODBII meter. Seems that I recall it was running about 9% at idle. I can compare with my daughters 2005 Accord to see if there is a difference. If the problem is with the AC throttle, then it must be off just very slightly since the problem goes away after the car has been driven a few miles.

 

That doesn't make any sense. There is no "AC throttle cable". The 2nd cable at the throttle is for the cruise-control.

TPS is throttle-position sensor, and they don't normally get carboned-up because they aren't an air-flow path. It's just a position sensor. It's the throttle body, throttle plate, and IAC-Valve that might get cruddy. With 37k miles they're probably still clean, but it's important to NOT take that stuff for granted.

 

Thanks for the clarification about the cruise control cable. I just assumed the second cable was AC control - never even thought about cruise control. I definitely have a repeatable process. If we turn off the AC before turning on the ignition, then the Park solenoid always works. If I pull the connector on the TPS, then the park solenoid always works. So I would say the problem is definitely related to the TPS. At some point, I will take the car down to the Honda dealership, but I want enough info to keep them from going on a wild goose chase in checking things that are not the problem. I did check the throttle pedal. If I press the brake pedal, I can hear the auto solenoid engage. If I then press in on the throttle pedal, then I can hear the solenoid release. Releasing the throttle does not allow the park solenoid to engage again. I have to turn off the ignition and then turn it back on - and the park solenoid works again.

 

Any updates on this would be appreciated. I am having the exact same problem with the shifter stuck at Parking. I've replace the stop light switch and adjusted the TPS. The voltage is at .47V at closed and 4.4V WOT which is kinda low. Not sure what else I can try next. Shifter works with the TPS unplugged.

Thanks

 

It's 04 Accord LX by the way -

 

My wife continues to turn off the AC before starting the car. The Park release solenoid always releases OK. When I drive the car, I make sure that the AC is on before I start the car. For the last few weeks, the Park solenoid is also releasing for me.

What procedure did you use to adjust the TPS? I think my voltage is 0.5 VDC at idle.

With my ODBII, I show 9% throttle position at idle and my daughter's 2005 also shows that value. I did notice something that is not right. If I press down on the brake pedal, with the ignition on, then I can hear the Park solenoid release. With the brake pedal still depressed, I step on the throttle pedal and I can hear the solenoid engage again. If I release the throttle pedal, the park solenoid does not release and I have to use the manual key to release it.

On my daughter's Accord, the park solenoid will release each time I release the throttle pedal - which I think is normal.

I wanted to get some sort of consistent failure before I take it to the Honda dealership for repair. I don't want them spending a lot of time to check things that I have already checked - especially tearing apart the console to get at the solenoid and wiring.

 

I did backprobe the voltage between the signal and the ground wires of the TPS at closed and WOT. I made a slot on the head of the temper proof bolts of the TPS using a Dremel, loosen the bolts so that the TPS is snug. I turned the TPS to adjust the voltage.

Also went to get the code read at Autozone and they told me no fault code was read. I've read that a bad cell in a battery can cause the shifter to lock in P; my battery is almost 4 yrs old. I asked them to check it and nope - it's good.

I am baffled at this point.