Odysseus Prime

1998 Civic DX

D16Y7 - stock other than intake.

I had some issues with this car several months ago concerning ignition and now I have some new troubles.


Not sure if the issues are connected or what.


So car starts right up every time, no issues. Idles fine. (I can let it sit there for an hour and it will gladly sit at 750-800 RPM the entire time)

the 1 problem happens after I drive it a few miles. Drives fine while under load, but once I come to a stop and the RPM drops to normal range, it continues to drop to around 200-300. Engine shudders a bit, but does not stall. Once it does this, I have to rev it to keep above 200-300. It will not idle at normal range once this happens

I would think this would be the IACV, but wouldn't this symptom pop up as soon as the engine got warmed up? Not once I started driving it?


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Now the other issue - the CEL - Do not remember the code #, but it popped a code for - bank 1, sensor 1 , system lean

So I pulled the Primary O2 sensor out of the manifold and it was covered in a 'white(ish)' residue lol. I replaced both O2 sensors with OEM ones. Car ran fine for like 2 days, then the code came back.

Side note - I replaced the manifold like a year ago because of a crack that formed right in the middle of ports 2-3. It popped this same code when that happened, but never came back once I replaced it with this manifold until recently. I do not see any cracks in this manifold I am using now.

So what else could cause this lean condition code to pop up? And could this code be the cause for the low idle? (IE - adjusting fuel=bogs the engine down?)





Things I have done / replaced, mainly replaced all this for previous IGN issues.

*NGK plugs
*NGK wires
*New Cap / Rotor / ICM / Coil
*New Main relay
*New fuel filter
*Timing was checked 2 months ago and is spot on factory specs


Not that it matters, but I've been running 89 Octane every time I fill up. Usually Shell. I have filled up 3 times since this issue has appeared from 3 different stations, so I doubt "bad gas" could be causing this.


I was going to take the IACV out and inspect / clean, but wanted some input about these 2 conditions and see if they could be connected somehow before I started digging around. Just weird that the idle is fine, even way after the engine gets up to temp, UNTIL I start driving it. Then it idles low. Really don't want to remove the IACV if whatever is causing the "Lean" condition is actually culprit of the entire problem.




Sorry for the long story lol. I just find that it helps the people reading to get the whole picture.

Turbobonics

Next time after a drive when car is completely warm, an fans have turned on, adjust idel screw on top of throttle, very slightly make the adjustment with car on,

An or top off an double check coolent system for air,

gameoverr96

could be your exhaust manifold gasket

gameoverr96

if your O2 is reading lean its gonna make u dump more fuel possibly causing your bad idle

Odysseus Prime

I will look into this tomorrow and see if that helps.

I will replace the gasket tomorrow since I have an extra one laying around. Then I will thoroughly check the manifold for any cracks that I might not have seen while it was on the car.

If there is indeed no cracks / leaks in the exhaust manifold, and I have 2 brand new O2 sensors, what could cause the Car to read "lean"???

00_civic757

check ur intake air temp. sensor.....if the iat sensor is not reading right then the ecu will think the air is warmer or colder than it really is and (in ur case it would be warmer since ur running lean) causing it to miscalculate the air/fuel mix.....it might read ok or with in specs at idle but under load as air is rushing into the intake tube and into the manifold, the sensor is sending a faulty signal to the ecu making it adjust to the much warmer air that it THINKS its getting when its really not causing poor idle.....this is the only thing i can think of since it only runs like that after u drove it

and btw running "LEAN" is too much air and not enough fuel..."RICH" is to much fuel not enough air

Odysseus Prime

I know what running lean is.

But thank you for the very informative post. How would I "check" the IAT sensor? Is there a voltage range it should be putting out or just go replace it to test it?

I have looked in the FSM and it shows to use a scan tool to test the IAT, and I do not have this scan tool.


Also. Wouldn't a CEL pop on for the IAT if it was giving bad readings?

gameoverr96

If there is indeed no cracks / leaks in the exhaust manifold, and I have 2 brand new O2 sensors, what could cause the Car to read "lean"???[/QUOTE]


any unmetered air will cause the car to run lean possibly a vacuum leak, intake or exhaust manifold leak, possibly a crack in your exhaust piping before the sensor (cant remember if your o2 is in the exhaust manifold or downstream before the cat) i would also go ahead and clean your IACV anyway because they will tend to cause some wierd idle problems

00_civic757

no not all the time.....usually if it has a short or open circuit and not working at all or just not there period it will throw a code but if its still sends a signal to the ECU even though its worng.. 9 times out of 10 it wont cuz throw one cuz the ecu still thinks its working

as for testing it....take ur IAT out and inspect it. Clean the sensor and connector off with ONLY electrical cleaner and after it air dries put it back in, plug it up,disconnect the battery for 30 sec. , and see what happens. If that doesnt work then call a buddy up that has a 96-00 civic and take his out and try it in ur car and then disconnect the battery for like 30 seconds to reset the ECU.....thats the quickest and easiest way to test it

00_civic757

very true but it wouldnt idle right if there was a vacuum leak and hes sayin it idles fine untill he drives it