ccoulon

Hi all,

Sorry to have another thread on problems idling but, I've tried most of the suggestions from other threads and still cannot seem to find the problem.

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 seemingly normal 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. Thinking maybe the throttle body was dirty I pulled it out and cleaned it, especially around the butterfly valve, but to no effect. 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. In addition I’ve run the car with a funnel full of coolant attached to the radiator hoping to release any air bubbles, but it didn’t seem to have any air in the system. The heater is also still working, leading me to believe there isn't air in it. I've done a vacuum test by spraying braking cleaner all around the intake manifold and all associated vacuum hoses but there was no change in the running of the engine. When the air intake housing was off, I blocked 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. With the TB blocked I again, used brake cleaner to try and find a vacuum leak, but could find none.

And finally I installed a new IAC valve and there has been 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, the codes were P0505, P1505, and P1518. 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 in advance for any help!

ezone

P0505: Idle Control System Malfunction (The PCM couldn't control the idle speed)

P1505: PCV Air Leakage (basically anything that could allow unregulated air: vacuum leaks in PCV, EVAP, brake booster, etc....Or a stuck open IACV.)

There is no P1518.... How about P1519?
P1519: IAC Valve Circuit Malfunction

Circuit malfunction.....Electrical problem.... Sounds like the IAC is getting pulled wide open electrically.. That explains the rest of the codes.

I would be getting out the voltmeter and doing some basic checks now.
With the engine running: check the connector on the IAC
Black wire is ground
yel/blk is battery voltage

Those 2 should be easy to check. If either isn't right, chase that problem first. A loss of either ground or power could make the IACvalve go fully closed or wide open.

blk/red is control from the PCM, may need a duty meter or a labscope to read it.
Checks for that wire are like checking continuity from the PCM to the valve, and checking that the wire isn't grounded or shorted.


HTH

ccoulon

Thanks for the quick response ezone, when I'm checking the voltage on the IACV should I be looking for a specific voltage or just simply that it is getting power and has a solid ground? If I find that it does have power and a good ground, would it be likely that the IACV itself is defective?

Sorry about the wrong code, I scanned it last week at a shop and wrote down the codes and have since miss placed that sheet of paper. I'm sure it had the 18 in it and it was registering something about coolant temp. low. When I went to re-scan it yesterday the only two codes that remained after my last ECU reset were the P050 and the P1505, I'm thinking the ECU has not had a change to complete all the system checks yet.

Thanks again.

ezone

The IAC has 3 wires:

One is battery power = battery positive voltage, whatever that is at the time you check it. 12v? 14v? It comes through a fuse and a relay before it reaches the IAC valve.

One is ground = battery ground (negative). Self explanatory?

One is a control signal from the computer. This is the one that isn't easily measured. The manual wants you to check continuity on the wire first, not check for signals on the wire.

No. You only checked 2 of the wires.
You didn't check the third wire yet.
Besides, the new valve does the same thing as the old one. Right?
AND there is a change when you unplug it, so the valve IS doing something. It is probably just doing what it is told.


HTH

mikey1

this is normally the sign of an intake air leak, it is sucking in excess air

ccoulon

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!

gwlindq

Re: 2000 Civic LX 4-Dooor w no spark
Thanks from another Civic owner. This one ran, then sat for a week, then w/n start... After I used my 94 Accord book to find wire colors, had 12v, had ignitor interruption, so went around the corner to Honda Dealer (Heard that loud and clear, but cost $120) bought a new coil and Voila! It Lives! Also changed and gapped new plugs I had around, and the best part is Wife is happy... FYI, can see burn mark on housing
Thanks again for diag tips and your knowledge...billl

Thanks again for all of the above, but now the vehicle, seems to run ok, but has 'hunting' idle. i.e engine idles a little fast, the at a few second intervals, suddenly drops very low, but then comes right back up to high idle, again.

I will check for any hoses I may have knocked off while changing the coil, but any words of advice would be appreciated ;-)
billl (gwlindq)