All of a sudden my 2004 2.4lt. I-VTEC started to Idle about 3000 RPM when cold. I'm not thrilled with waiting 5 minutes for it to warm up or slamming it into drive at this RPM. It also started down shifting poorly. After a few weeks of this it reported a throttle position sensor error. I replaced the sensor and calibrated it to .45 Volts and have not gotten the error sense. Resetting the computer was required to fix the transmission shifting, however the cold fast idle problem remained the same. From what I understand the Idle Air Control Valve (IACV) controls the idle when cold. It seemed logical to replace IACV sense the computer can't detect a failure, so I did. This also did not affect the cold fast idle problem. I'm not finding any vacuum leaks. Plugging the Cold Idle Valve did help but only like you would expect given it's function. Anyone know what's going on here?

 

I've also checked the PCV valve and break booster. I even had the local Honda dealer take a look at it. They can't find anything wrong. I did have them verify the throttle position sensor voltage and temp sensor, but they checked out good. Seems something is throwing off the PCM. It seems to be telling the IACV to idle fast and erratically when cold.

 

I've been looking through the Honda service manual, unsure of what to do next, then this morning my wife reports the submarine light is lit up on the dash. I quickly run out and connect up the code reader and get P0122 the throttle position sensor (TPS). Now this is strange because I have already replaced and calibrated it. Then had Honda Service verify it was calibrated correctly. They reported it to be dead on. .5 Vdc closed and 4.5 Vdc open. So now what, follow the wires from the TPS to the PCM looking for damage?

 

Check your MAP and other intake sensors. Check/replace the air filter.