Hi Folks,

I've been chasing this problem for quite awhile now- hoping someone can shine some light on the subject.

Specs: 2000 Honda Accord 4Cyl VTEC, 150K miles

Problem: intermittent rough idle, stumbles until I get on the throttle, then accelerates and runs clean. The exhaust note at idle almost seems like it has a misfire. When I pull the plugs, they are tan and clean, which makes me think it's not a bad cylinder.

Also, it doesn't do it consistently. It will run smooth in the morning, but in the afternoon it has a rough idle, for example.

What I've done/replaced so far:
-Fuel system cleaner
-Cleaned throttle body
-New Air Filter
-New plugs & wires
-New IACV
-Cleaned EGR Valve
-Valve adjustment
-New PCV Valve
-New Ignition rotor/cap

After replacing something, it seems to helps little bit, but the problem still persists. The most recent thing I did was the rotor/cap. Before I replaced these, the engine would almost want to die at idle. Now it's much better, but still hesitates/stumbles at idle.

It's giving me codes P0420 (bad cat) and P1457 (EVAP canister/solenoid).

Internet research and a mechanic have both told me that the bad cat is likely a result of the poor idle, not the cause. I've also been told the EVAP does not effect how the engine runs. I'm waiting to fix these issues until I pinpoint the rough idle.

Any thoughts?

Thanks!

 

check mechanical timing, could be off a tooth

if good, compression test to be sure the engine is in good shape

 

I would check for a vacuum leak around the intake area using carb cleaner or water. Possibly check the MAF sensor and give the contacts a good clean with electronic parts cleaner.
What kind of plugs and wires did you use? Hondas are very picky about their spark plugs. They even go so far to list specific part numbers for the plugs (Denso or NGK).

I, too, recently had the p0420 code. I would replace the the cat O2 sensor at the cat and see if that takes care of the P0420 code. if not, I put a magna flow direct fit on mine and it works great no more code ( I think it was like 150 ish on Amazon).

 

none of the cars in this subforum have a mass air flow sensor