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Self-revving engine?!

I just got a new-to-me 2002 Honda Civic SI hatchback and while I understand that everyone hates traffic, my car absolutely despises it. In dead-locked stop-and-go traffic where I usually don’t get above 2nd gear before stopping again, after 5 minutes my engine will begin to rev up to 5,000-6,000 rpm even when I am idling. It sounds like I am mashing on the clutch and the gas at the same time, but only the clutch is depressed, and it continues even if I slip it into neutral and take my foot off the pedals. Again this ONLY happens in stop-and-go traffic or line-waiting, and I don’t know how to get rid of it except by driving again. What is happening?! I recently took the car in and had the transmission done to no avail. I like to believe my car is just displaying my emotions about being in traffic, but surely it can’t be good for him. Help?!

I recently took the car in and had the transmission done to no avail - ?? You might want to elaborate on that. What was done? And was it done in relation to an idle problem? That would be strange. Did whomever that did whatever with the transmission look at the idle problem at all?

I think your two best possibilities are either a throttle body problem or idle air control (IAC) valve problem. First just check the throttle cable, linkages, return spring etc. to make sure the throttle plate isn’t sticking open. Inspect the throttle body for excess carbon buildup as another possible sticking source. These kinds of problems are not hard to correct.

For the IAC, one thing you can do is to pull over the next time it idles high and give the IAC a sharp whack with something like the handle of a screwdriver or block of wood. See if that does anything. These are easy to clean or replace.

All of that is assuming that the idle is not surging up and down or associated only with the brake pedal (but you said it continues with you feet off of the pedals).

I recently took the car in and had the transmission done to no avail

Before I bought the car from a private party I took it to a Honda dealership and they did their safety inspection on it, tearing it apart and putting it back together, and provided me a list of everything wrong with it. One was that the transmission needed servicing, so that is what I did. The rest of the list were things like strut boots, oil cap, breaks, roters, sway bar, things that probably don’t apply but I had them fixed too. I did not take this particular problem to them because I want general ideas of what it is before having them take the car apart again, especially if they didn’t catch it the first time - about a month ago.

Thanks for your help, I don’t know any of the terminology you provided but it is great having something to further investigate.

Having it checked out before buying it was the ideal thing to do - points to you for thinking.

A couple of points. First, you don’t need to have a dealer service this. They have nothing magic over independent shops - they mostly only have much higher prices (for parts and labor) and sometimes corporate orders to find reasons to fix things. Find a local, independent shop - one that specializes in Honda would be good but not necessary for a shop of good reputation.

None of the things that you mentioned in their check up would have anything to do with the idle problem, and this is the kind of thing that can happen at any time and wouldn’t necessarily show up on a pre-purchase inspection.

Presumably you mean “tearing it apart” figuratively b/c very little, if anything is actually taken apart when one goes over a vehicle. The wheels are pulled, and maybe some incidentals like splash shields, but nothing is torn down. Nothing needs to be torn down to check out the idle problem either.

Is the check engine light on?

I took it to the Honda dealership initially because I thought they would be better at spotting honda problems that a general fit-it shop could not. Now that I know what it may be, I would definitely feel more comfortable going to an every-day mechanic, and actually just looked up a couple on the “mechanic files” site recommended by the brothers.

The service light was acting strange recently… When I turn the car on it would blink several times after the other lights have gone off, and then it too will turn off. I looked in the owners manual and it said that if the light has never been reset, it will automatially start blinking like this after 10,000, and then if nothing is done about it again it will stay lit after 15,000 miles. SO I figured the guy before me had never had it reset, that I had just gotten all the Honda recommended work done on it, so I reset it myself. Now it is off and has not been back on since… that was about 2-3 weeks ago.

And yes, that was figurative… I would never let anyone tear my car apart :slight_smile:

I recently took the car in and had the transmission done to no avail.

Can I assume that “had the transmission done” means you had a fluid change, or if they talked you into it, a transmission flush? Once you see problems it is too late for a fluid change.

You change the fluid to prevent problems. Often problems are caused because you have not changed the fluid. Maybe if you changed the fluid 40,000 miles ago, that may have prevented what you have now.

How is old transmission fluid or long service intervals going to have anything to do with the engine revving up at idle - and with no feet on the pedals? It also appears to be a manual - so even if there was some clutch slippage creating rev (which doesn’t fit the description) this has nothing to do w/ the trans fluid.

It has happened again while sitting in the muck of 2 hour Chicago traffic, this time enough so that I had to pull over for fear that my engine would overheat. I wacked the IAC, I see no problems with anything, all sensors and vacuum hoses connected and secured. I let the car cool down, got back on the interstate, and was able to drive my car much like an automatic: not having to use the gas, simply releasing the clutch would cause the car to go forward and it wouldn’t roll backwards even with only the clutch in.

I have been looking for other forums where this exact problem has been described, and a Subaru WRX discovered his identical problem was all about heatsoak to the cruise motor. It was fixed by loosening the cruise control cable slightly at the adjustment perch in front of the throttle body. It was said this helped because “the cruise control box on the passenger side firewall (black box by turbo/downpipe) distorts slightly under the heat of stop & go traffic during hot days and pulls on the cruise control cable.”

Have you ever heard of this? Neither of us were using cruise control when this problem occurred, does that matter? I am curious to hear what you think!

I would like to add that when this happens, there is no indication on the dash that anything is wrong, except the high RPMs. The check engine light has not come on, the temp is cooler than mid-line.