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I have a 1998 Honda Civic DX 1.6. When im driving, the car is fine and runs perfect. But when I push in the clutch and the car idles down it runs rough. It also does this when i come to a stop and the motor idles down and it runs rough but then it increses the revs slightly and runs fine. What could the issue be? I replaced the spark plugs. Just dont wanna start throwing parts at it hoping i fix it

 
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Did it do this before you did the timing belt job?
Did you get the cam timing a tooth off?

 
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Yes it did. I dont believe so. I checked the timing at least 5 times

 
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Also, before i did the timing belt it was throwing a CEL code. I cant remember the code exactly but it was something about system emission below threshold or something like that. But its not on anymore as i disconnected the battery. Itll be back on when i drive it tomorrow. could that have something to do with it?

 
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I'll take a wildass guess at a cat code. No, that wouldn't cause your idle problem.



Rough at idle......Have you checked compression yet?

 
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I have not. I will though and let you know what i get. What kind of numbers should i be looking for? Also, if its losing compression, wouldnt it run crappy all the time?

 
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Do the compression test, post your results.

Pull all spark plugs out, and disconnect the harness plugs from the distributor (so you don't ruin the coil).

Install tester on first cylinder and crank it until the gauge stops climbing, plus a few more hits just to make sure that's all you are gonna get from that cylinder.

Repeat the same for the rest.

 
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Alright, Just did a compression test in all 4 cylinders. Just shy of 150 in all 4. Cant give exact as my tester goes from 130 to 150 and doesnt show much in between

 
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Compression result numbers are all within 10% or each other?


Is the idle rough as in a miss, or just low?

Does the engine have an EGR valve?



Vacuum leak?
Ignition timing retarded?
Clean throttle body?
Reset minimum air rate and base idle speed?
Idle learn?




Man, I can only guess from here.

 
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Yeah, all the numbers were all very close. So i guess ill rule out total ctastophic engine failure. It isnt a miss. When i push in the clutch it idles down really low like its about to stall for about 5 seconds then comes back up. I cant really read my revs as i do not have a tach at this point. My next step is plug wires, cap and rotor, clean/replace the IAC, clean the throttle body. How do you do an idle learn and reset the minimum air rate? If none of that fixes it, im chalking it up to old age and the 185k miles on it

 
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Not too sure about the EGR valve but ill look in to that. thank you for all the help. hopefully with your suggestions i can get it fixed

 
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The numbers are low for my liking, but that might be attributed to your test equipment or something.. I like to see 180 and higher out of these engines.

Since it's not a miss, I wouldn't toss any of those parts at it. Unless they are really needed, of course.

You say it picks the idle up again, so I expect the IAC is also working.
This. Much of this. Throttle body bore and throttle blade, all around the edges of both sides. Carb cleaner spray and toothbrush.

Do this after any other work is completed and fixed.

Di it now, just to see if it helps..... but it needs done after any work that can affect running, or battery disconnect, or memory and code clear/PCM reset.

Get it all warmed up, turn off everything electrical, and let it and idle for about 10 minutes.

What engine code does this have?
Which trans does it have?


I only asked if it has one.

 
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It was a SUPER old compression tester, so i wont do any wires then as theyre not needed. But today on my way to work it ran perfect. Not a single problem, no CEL. On my way home, CEL came back on and started to have the idle issue again. So im gonna take a shot and say whatever is causing my CEL is also causing the issue. But im still cleaning the throttle body

 
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So for the idle learn, when i get home from work turn off my light and radio and climate control and just let it idle for 10 minutes?

Because now that you say to do it after i clear the code, i cant say i really recognized this problem until after I cleared the code when i first got the car. So ill try that as well.

 
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Yes, start there. What's the code this time?

Pretty much. The books say 5 minutes, but whenever the fan runs you are supposed to stop the timer while it's running since that's a large electrical load.
So I figure 10 minutes ought to cover it.



In Honda world, there is "clearing codes" and there is "PCM reset". Relearn is necessary after performing a PCM reset, PCM lost power, battery disconnect, dead battery, etc., in addition to needing done whenever something in the engine gets changed that can affect idle.

Many non-factory scan tools will cause a PCM reset when codes are cleared. It gets the codes cleared all right, but it also erases the memory of "how to idle" (learned parameters).

The factory scanner can perform either function independently, as needed. I can clear codes without wiping out the learned memory.

 
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Alright. That I did not know. I will have to check the light at some point this week and I will let you know. Thank you for all your help.