1998 Honda passport muiti codes

and update, so I ended up pulling the battery off for a hour or so, it no longer runs at 2800 rpm, but won't idle either, and doesn't smooth out until I get above 1500 rpms, everytime I clear the codes they come back instantly, does this sound like a pcm gone bad, the engine is a 3.2 liter with a automatic and two wheel drive.

You have 3 separate problems, P0402 and P0406 are EGR valve related. P0453 is an inoperative Fuel Tank Vapor Pressure sensor and P0123 is an electrical problem involving the Throttle Position Sensor (TPS).

If the EGR valve is stuck open the engine will not idle properly.
If the TPS is inoperative the engine will not respond correctly to accelerator changes in throttle valve position because the PCM does not know the actual position of the throttle valve.
If the Vapor Pressure sensor is inoperative the EVAP system leak test will fail, but no EVAP system codes are set. Are you sure P0453 is set?

Troubleshoot the TPS problem first.

Buster28 said:

You have 3 separate problems, P0402 and P0406 are EGR valve related. P0453 is an inoperative Fuel Tank Vapor Pressure sensor and P0123 is an electrical problem involving the Throttle Position Sensor (TPS).

If the EGR valve is stuck open the engine will not idle properly.
If the TPS is inoperative the engine will not respond correctly to accelerator changes in throttle valve position because the PCM does not know the actual position of the throttle valve.
If the Vapor Pressure sensor is inoperative the EVAP system leak test will fail, but no EVAP system codes are set. Are you sure P0453 is set?

Troubleshoot the TPS problem first.

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yes all these codes came on at the same time, and come back instantly after clearing them, which is why I'm beginning to think the PCM is bad, going to try and find one at a wrecking yard for the same year and engine, all the sensors seem to me ohming out correctly, what else would make all theses codes pop out at the same time, and return instantly after clearing them, without ever starting the engine, Anxiety is making this so much more difficult than it should be.

billmitchell89 said:

yes all these codes came on at the same time, and come back instantly after clearing them, which is why I'm beginning to think the PCM is bad, going to try and find one at a wrecking yard for the same year and engine, all the sensors seem to me ohming out correctly, what else would make all theses codes pop out at the same time, and return instantly after clearing them, without ever starting the engine, Anxiety is making this so much more difficult than it should be.

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oh and something else I just discovered , is the transmission over heat light is on, and a second code reader that reads the cars temperature, says the engine is running at 298 degrees F, and thats not true, the car is running at 180 F .

OK so here's the update, I went and picked up a used PCM from a local junk yard, installed it as a test, and low and behold, the darn thing fired up idled right and no codes, took it for a short trip around the block and it seems a lot better, I'll update again in a week or so, but so far even the high idle problem that I had for the past year seems to be better Aswell.

You should put the old PCM back in and see if the codes come back. That many, and varied, codes makes it seem more like a connection issue. I wonder if something was loose, and you just properly plugged everything back in when switching the ECMs.

Enemigo said:

You should put the old PCM back in and see if the codes come back. That many, and varied, codes makes it seem more like a connection issue. I wonder if something was loose, and you just properly plugged everything back in when switching the ECMs.

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I had actually pulled the original unit out and cleaned the connecters, and put it back in just to get a ideal what to expect at the junk yard, hares the kicker, after replacing the entire unit and confirming that the car runs right, which it seems to so far including the problem I had with the random high idle issue, I went ahead and opened the old pcm cover, and found that it has a removeable chip in it, so my plan is to save that chip and one day when I have more time pull it all out again and change that chip just to see what it does, My next step is to take it out for a long drive to check the Milage, hoping to get better then 14 MPG, lol.

Glad you found a quick solution.