Honda Car Forum

Hello, First post on this forum,

I tried searching but did not really find what I was looking for.

I have a 99 Civic LX 4cyl. Auto Trans.

Car has 95,000 miles on it. No issues until today.

This car has been stored in my garage for the last 4-5 months.
Everything ran fine until today.

I went out to start it to make sure the battery was not dead, Started up without issue. and idled fine for approx 10 mins.

Then the engine started reving up and down. Betweeen 1k and 2k RPMs.

When I put the car in drive it leveled out at 1k just fine. Same in Reverse. (when there was a load on the engine) Back in park or neutral and it would start reving again.

I turned the A/C on and it would level out. Turn it off and it would start revving.

Then the check engine light came on. I turned the car off at this point.

I popped the hood and looked in the air cleaner to see if may a mouse had gotten in there. nothing all clear.

It doesnt have a plate on it right now, so I cant take it down to see what code it may have thrown.

Any ideas. Im thinking maybe a sensor is plugged or something with the intake? Plugged fuel filter?

Thank you in advance.

Okay, So I am pretty sure the code that its throwing is for the idle air control valve. Is this something that would just "go out" after sitting for a few months.

Is there any way to clean it?

I have also read that the coolant level has something to do with it. I have checked the coolant level and its full. The car never had a coolant issue before, and I looked under the car and there are no leaks. So Im not sure that I would have lost any coolant to mess with the idle air control valve.

I also found this link to check codes. Pretty nice and saved me a trip to autozone.

The new cel thread (how-to & codes) - Honda-Tech

Well, I did some more research

Replaced the PCV valve with an OEM one. (21 bucks)

and took the Idle Air Control Valve out, cleaned with throttle body cleaner, (5 Bucks) and some q tips. Let it dry, re installed and now its good to go.

For what its worth this was on a 99 civic LX (non Vtec) and the Haynes manual was no help at all. Photos and write up on the IACV were not for this engine. (yes I had the correct manual)

I ended up getting some exploded views of the engine from the dealership which were pretty straight forward. since the part in the haynes manual looked nothing like the part on the car.

Hope this helps someone else out.

I have the same problem with mine. It revs up and down continuously, but it doesnt matter what gear it is in. I have no check engine light, but it has had a tune up recently with new spark plugs and wires. I wonder if that could have something to do with it?

Mine was fine in Drive or in Gear. It would only rev up in Neutral or Park, as the engine did not have a load on it.

Im not sure about new plugs and wires, unless one of the wires is loose?