Hi All,

I am having issues with my 2002 Honda Civic DX sedan. It has been having a relatively rough idle for about a month now (at first I thought it might be a missfire), and then about a week ago my wife stalled the car at a red light, I think the jerk of stalling on the engine might have something to do with the deteriorating condition. Since she stalled it the car has remained in either two different idles. Most often and always at start-up the car will fluctuate consistently up and down between a idle and a relatively fast idle (sorry I don't have a tachometer) and occasionally, seemingly after the car has become warmer, but not always, for short periods of time it will switch to very low idle where the car is shaking and again feels almost like a missfire. It doesn't seem to really change a whole lot overall between being cold, warming up and and warmed up. The Temperature needle is functioning normally, slowly rising while warming up and then resting around halfway.

The car has also become much more rough to drive, anytime I am coasting at the speed limit and let up off the gas pedal the car tends to lurch and then again when I begin to depress the pedal it lurches again, this makes for very lurchy driving. Finally, every now and then I can smell burning/excessive fuel leading me to believe the car is running rich.

So far I have checked the coolant level, which seems to have good pressure and is full at the radiator. The heater also works great still, leading me to believe there isn't air in it. I've done a real quick vacuum test, that could probably have been more thorough, but since it hasn't really been nearly stalling at all in the strange idle and the fluctuating seems very consistent I wrote off the vacuum leak for now. And finally I installed a new IAC valve yesterday and there was no change. Immediately after the new part was installed I started the car up and it was fluctuating still. I have reset the ECU/idle learn several times including immediately after the install of the new IACV and doesn't seem to have any effect.

I managed to get the car to a shop where they scanned it for me and I believe the codes were P0505, P1505, and P1518 (definitely not P1519), sorry for not knowing for certain, I wrote them down but they seem to have been thrown out during house cleaning. The two P0505 and P1505 were in regard to an idle malfunction and the P1518 from what I remember said the engine coolant temperature was off (too low maybe).

Does anyone have any ideas what I could/should try next? At first I thought maybe looking for a Fast Idle Thermo Valve, but I can't seem to find any information on one for this model, which makes me think this model doesn't have one...

Thanks again!

Chris

 

Does it still accelerate / climb hills normally? If not you should look for more fundamental problems like skipped timing belt or dead cylinders.

Lurching when you first press the gas pedal is often dirt in the throttle body making the throttle plate stick to the sides.

 

When the car is in gear and the gas pedal depressed (however much) it runs like normal. It seems to only lurch when it is transitioning from no throttle to some. Don't know if this makes a huge difference but the timing belt was replaced about 6 months ago and it did not have any issues before this incident. I'll take another look at the throttle body to see if it is dirty, last week I used some TB cleaner, sprayed direct into the TB in hopes of fixing the idle problem, but it didn't have any effect.

 

Alright, I've managed to re-scan the car the only codes that are now showing are P0505 and P1505, both having to do with idle malfunction. I've cleaned the whole throttle body, especially around the butterfly valve and it has not made any difference. This last time when I had the intake housing off I blocked the intake on the TB and the car immediately resumed a consistent idle, perhaps a little higher than what the normal idle should be, but much better than the fluctuating idle it has been. As soon as I removed my hand it ran for a moment or two and then resumed the fluctuation. I also unplugged the IACV and the car immediately dropped to a very low rpm idle and shaking the whole car a bit. Both while the TB was blocked and not, I tried again to test the vacuum with brake cleaner and sprayed all around the intake manifold and all vacuum hoses, but there was no affect on the engine running.

Could it be possible that the IACV replacement I got was also defective? I received it re-manufactured, but supposedly they test all their products before shipping them out...

Thanks in advance for the help!

 

Figured it out! The vacuum hose that attaches to the PCV was not OEM, a previous owner had replaced it with a very soft/spongy, too short hose and it had vibrated off. The valve is located near the bottom of the engine so all three times I tried to find a vacuum leak by spraying brake cleaner around the intake manifold and hoses coming off from it, I missed this one. I managed to get a hold of a smoke vacuum tester today and figured it out pretty fast. Took me about 5 minutes to replace the line with a longer, more sturdy one and actually put on hose clamps for good measure, car idled great after that.

Now that I know that the IACV was not the culprit, would it be advisable to keep the new one? I've been reading that these can be a common problem on these cars and may inevitably need to be replaced at some point anyway. The car is at about 130,000 miles. Just wondering if I should try to return the new one or sell it on ebay or just keep it in?

Thanks again for all the great advice!