99 Honda Accord V6 Rough Idle When Hot

I have a 1999 Honda Accord V6 with an automatic transmission and about 180,000 miles. Problem is that when I start the engine after it’s already hot, RPMs go very low (around 500) and engine is so rough seems like it will stall. To prevent stalling, I give it enough gas to keep the RPMs above 1000; after putting the car in drive and it gets rolling, the problem goes away quickly as the RPMs rise during normal course of driving. Never any troubles while the car is driving or in gear (like when I stop at a red light). Only happens in the first few seconds of idling when engine is hot until I get out of Park and driving. Never any problems on cold starts (RPMs then seem to be in normal range).

Any ideas what this could be?



Washington, DC

Here are a few generic faults:

  1. Dirty air filter
  2. Bad engine ground connection
  3. Fuel supply fault
  4. Loose connection in the ignition system
  5. Faulty emissions systems

Those are good for a start but there are other things that can cause your problem as well.

I just had this same problem (albeit with the 2.3l 4 cyl engine). I checked all the sensors, the air filters vacuum lines, etc. with no luck. I saw some posts about the Idle Air Control Valve (IACV) getting dirty sometimes, and since I had a can of throttle body cleaner, I ran in through the main throttle body and the bypass tube that leads into the IACV (followed manufacturers directions on the can) and everything is good now. You’ll need to turn the throttle plate open while you spray 'cause it really slows down the engine while you’re spraying.