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Low Idle Mystery - Part 2

Thank you for all of your comments and advice - This weekend, I took my 98’ Honda Civic Ex to an independent mechanic for spark plug service. They also agreed to give it a look over to get to the cause of the low idle - which is also slightly rough.

They checked the valve adjustment, did a smoke test to look for a vacuum leak, and and cam timing - all were fine, no vacuum leaks, etc.

For those who may not know from the previous dicsussion, the car has 118K and is a 4-cylinder automatic, v-tech engine.

What I have done:

Got a new Honda distributor

Transmission fluid fush

Cleaned the throttle body

Cleaned the Idle Air Intake Valve

Used Gum Out fuel injector cleaner

Had a diagnositc done at Honda (they found nothing suggested cleaning the IAC)

Now, new spark plugs

Smoke test

Valve adjument check

Cam timing check

Has anyone else run into symptoms like this and figured out what the mysterious problem was?

Also for those who don’t know, the symptoms are a low rough idle at redlights, or while idling in a parking lot. It shakes more heavily at some times. Every now and them it idles so low it threatens to stall - more of a warm weather symptom though. When I am driving at low speeds, and I transition from coast to accelerate, sometimes it jumps slightly. When I am coasting downhill at a moderate rate, and have to come to an abrupt stop, it jumps. Once I am accelerating, it runs fine. No check engine light.

All advice is appreciated - I feel like the dealership has been milking the issue to make commission. I am sure with the bad economy, a lot of people are under extreme pressure to show they can sell.

Thanks for your time!


Have they done a compression check? With all this other work done, maybe the condition of the cylinders needs to be examined.

They have not just yet, but I am letting that independent shop hold onto it for the weekend. They did mention they suspected it might be related to one of the cylinders. If it is an issue with a cylinder, does that lead to an expensive fix?

Thanks for your response.


At this idependent shop, not sure that they checked compression. They said that would be the next step, but when I picked it up, they said the fuel filter looked like it had never been changed. I had mentioned that to Honda, they didn’t seem to think it was the issue. It idles better, not as rough. Drives better. Still jumps a little in low speed bumper to bumper type traffic. Wonder if more dirt is floating around in the fuel system and needs to work its way to the new filter?

Hope less than smooth transitions are not a sign of a worn out transmission. One thing a Honda technician told me is that when a transmission starts to go out, it will rev up slightly when shifting to idle or between each downshift. My car does this, but I am not sure if that’s the case.

Shop I just left didn’t mention anything about the transimmion.