agb22

Hello Civic Forums:

I own a 1999 Honda Civic EX. D16Y8 Engine. The engine light has been going on and off with the same code for the Idle Air Control. The car had high idle when I started it up. The Idle would also go between 1500 to 1700 rpm while Idling. I decided to do some of these tests.

- Checked for air in the cooling system, that seemed to not be the problem
- Checked for vacuum leaks, did not find anything
- Tested IAC by tapping with screwdriver butt, no change in idle
- Cleaned IAC and throttle body with carbon cleaner and replaced gaskests

After cleaning I started it up and let it idle for a while. It seemed fine. Idle was back to normal position. I took it for a test drive. The car was driving fine for about 10-15 minutes. After the engine really warmed up the rpm started randomly dropping while I was driving. Driving about 35 mph @ 3000 rpm, it would randomly drop down to 2000 or sometimes even 1500, and then spike back up to around 2500, back down, then back to normal driving. This is happening while my foot is on the throttle. It was repeatedly doing this every few minutes.

This is currently where I'm at thinking about what to check next :

- Relearn Idle
- check PCV / Replace
- Replace IACV (already cleaned it, didn't seem to help)

Suggestions on where to go next in diagnosing the problem? Thanks in advance!

RichInWA

I had a similar problem with a '99 and my mechanic replaced the TPS [throttle positioning sensor] right near the firewall..........
Not a mechanic, but the surges in idling fixed.
Dick