My son bought a 2002 Honda Accord, 130k miles (4cyl). It's in great shape, runs unbelievably well. If it's idling in park it's pretty smooth...and when you give it gas it couldn't be a smoother ride.

But when we are idling in Drive, it has a pretty rough idle. I can feel it cycling, as the idle seems to increase, and then drop off, rinse/repeat.

We've checked the mounts, and all seem to be good. We've cleaned out the air intake, cleaned the throttle body, replaced the spark plugs, and ran some fuel injector cleaner through the fuel (last two fill-ups).

I'm thinking the fuel injectors still need to be cleaned better. Any Thoughts/Suggestions?

I considered the MAF, but it's accelerating smoothly, no misfires, etc...so I maybe ruled it out prematurely.

Is there a way to check that, other than replacing it? I guess I can spray it with some CRC cleaner and reinstall...

Spray it, clean with a Q tip until no more dirt and whatever comes off. I have to do it with my '00 Celica every 5-7 years.

yeah, just clean it very gently with a q tip

May also want to clean the throttle body if possible.

Cannew said:

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May also want to clean the throttle body if possible.

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Done that. Good suggestion though

Do as others have suggested . If it still idles rough, hook it up to a laptop or a code reader to check fuel trims and check for misfires. Fuel trims can help identify intake or exhaust leaks. You could do a fuel pressure test and then check the fuel pump, fuel filter, and fuel pressure regulator.

How were the plugs? black and sooty? or an off white?

I'd double check the mounts.

It's hot out. Does it it idle rough in drive with the AC off? It is likely rising and falling to compensate for your AC compressor cycling on and off.

The AC doesn't affect it, we've tested that option. If cleaning the MAF doesn't affect it, I'm going to clean/replace the fuel injectors and will report back.

Thanks for the suggestions.

fixer said:

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How were the plugs? black and sooty? or an off white?

I'd double check the mounts.

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plugs were a little dirty and a couple starting to corrode. Not terrible though for a 2002. I'd say closer to off white than sooty..but definitely needed replacement

Ok that is good sign that your combustion chamber has integrity and not causing a misfire.

Only other remote thing it could be is a weak alternator dropping voltage enough to cause weak spark.

I'd be checking the mounts very thoroughly.

I had a 2009 Accord that did that off and on; the culprit was almost always the MAF. On my Accord, the MAF was built into the throttle body assembly and couldn't be removed to clean/replace separately. If the car is higher mileage, I wouldn't rule out replacing it as a fix.

hijakeroo123 said:

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I had a 2009 Accord that did that off and on; the culprit was almost always the MAF. On my Accord, the MAF was built into the throttle body assembly and couldn't be removed to clean/replace separately. If the car is higher mileage, I wouldn't rule out replacing it as a fix.

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Good to know.

It's crazy how butter smooth it is otherwise....unless I'm idling in Drive. Helps narrow down the issue, but if I can get that figured out, we're good to go. This thing amazes me, how good it runs and how good of shape it's in after 22 years.

I would take off the filter housing and just try cleaning the Maf and the throttle body, might be all it needs.

PCV valve or vacuum leak somewhere?