Just purchased a 2008 Accord 4cyl VTech engine. Drives great but has intermittent rough idle (worse with AC on) and have gone to two shops but no one seems to know how to fix it.

Did valve adjustment, tune up and drive belt service but didn't change anything. Anyone know what it might be?

 

Just moved you here to the correct question thread..|Welcome to the HAF..

 

Check Engine Light on? If yes, get the codes and post them.

Suggest cleaning throttle plate front/rear and throttle bore w/ throttle body cleaner. There are a number of warnings on throttle body cleaning (must remove throttle body). Don't spray directly, clean w/ rag w/ throttle body cleaner on rag, use honda throttle body cleaner.

ECM must be reset (requires obd2 scanner at least) and idle relearn procedure should be performed after throttle body cleaning.

A honda shop manual is essential (see automanualsource.com for a download).

good luck

 

I’ve got the same going on with rough idle and worse with the AC on. 2008 Accord 2.4L with 133k miles.

All done so far:

Induction service
Fuel injector cleaner ran through gas
Throttle body cleaning with idle relearn
Replaced the three motor mounts, all OEM (trans mount on backorder)
OEM spark plugs at 115k
Valve adjustment done at Honda at 117k
Replaced VTEC spool valve gasket
New engine air filter
Replaced intake duct as original was cracked

Car runs fantastically outside of a rough idle. There is no CEL and no stored codes.

 

You might check your distributor for oil intrusion. 133K would be right in there for when this common issue comes up. Any oil leaks showing beneath the distributor? If so, pull the cap and look inside at the bottom edge. If you see oil pooling, it's time to either get a new distributor or replace the seals. At least the 4 cyl has a replaceable inner seal, as the V6 doesn't seem to. Good luck.

 

The 2008 doesn't have a distributor. Do you have a scanner that can read live engine data?

 

Ah, thanks. I should have realized it would be coil-over ignition. Never mind. ;-)