[2007Accorddriver]

Out of curiosity, how long does it take your car to fall to idle speed from a cold start? I noticed on my mom's brand new pilot it was within 10 seconds of a cold start that her car was idling.... meanwhile my 07 Accord starts, goes to 1,500 rpm, and takes about 5-6 minutes to fall to idle speeds of 7-800. Anything I can do? Possibly need to relearn idle or clean/replace thermostat? I can't imagine this was normal when new in 2007.

For reference, this is happening in 60-80 degree temperatures right now. It also occurs in cold temperatures.

 

[Ash051]

It's normal for our cars to idle a little higher with cold engines. Once the engine warms up to normal operating temperature, idle should fall to around 700 or 800.

Don't compare a 2007 Accord to a brand new Pilot- it's like comparing apples to oranges.

 

[mtts60]

mom's brand new pilot it was within 10 seconds of a cold start that her car was idling.... meanwhile my 07 Accord starts, goes to 1,500 rpm, and takes about 5-6 minutes to fall to idle speeds of 7-800. Anything I can do?

Brand-new Pilot has brand-new coolant, tight engine, different computer and operating parameters.
2007 Accord has X-year old coolant, loose engine (that's completely different from the Pilot) and a different computer.

Like our Gearhead Girl said, not even close to the same.

 

[dslnut]

Out of curiosity, how long does it take your car to fall to idle speed from a cold start? I noticed on my mom's brand new pilot it was within 10 seconds of a cold start that her car was idling.... meanwhile my 07 Accord starts, goes to 1,500 rpm, and takes about 5-6 minutes to fall to idle speeds of 7-800. Anything I can do? Possibly need to relearn idle or clean/replace thermostat? I can't imagine this was normal when new in 2007.

For reference, this is happening in 60-80 degree temperatures right now. It also occurs in cold temperatures.

Our 03 2.4 does it for a few minutes (not 5), its all tuned, clean TB etc. and running good.
I remember something about warming up the catalytic converter quickly.
I dont remember my domestic brand vehicles doing this.

 

[jmaraist]

The computer monitors your engine temperature and adjusts the RPM toward normal idle from cold.
The "temperature variable" resistance in the engine temperature sensor may be higher than normal due to corroded contacts where the wiring harness connects to it. Locate it and remove the connector and look to see if there is any discoloration on the contacts. Reinsert the connector and remove it several times to cause the contacts to bite into each other and remove any resistance caused by what is now an older car that is susceptible to contact corrosion.

The computer puts out 5 volts into many of the engine sensors. The temperature sensor at operating temperature is about 200 ohms ( Reference boiling is 212 degrees so the resistance is around that number) When the engine is at a starting temperature of about 80 degrees the temperature resistor is around 2,000 ohms, if the engine temperature is near freezing the resistor will be around 5,000 ohms. This was measured on a GM so the Honda temperature sender resistor might vary but the principle is the same.

The computer puts out 5 volts in another of my cars and a hot engine temperature sensor (at 190 degrees or 200 ohms) will return nearly 5 volts to the computer which has a program to determine the idle RPM and the mixture richness to meet emissions and to not stall out. With a just started colder engine, there will be a higher engine temperature resistance and a lesser voltage will be returned to the computer which is why it idles fast when cold and slows down as the engine warms up. The computer varies mixture richness and RPM according to this returned voltage.

Any corrosion in the contacts will increase the resistance and cause the engine to idle higher longer. Removing and reinstalling the wire harness connector should eliminate any unnecessary additional resistance reducing higher idle longer than necessary.