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Old 11-25-2011, 05:23 AM   #1
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Default idle problem after over rev

hello,
i had a miss shift and over revved my b16. ran out of oil then i changed the oil and motor seems to be somehow fine. the problem is that after the engine warms the idle begins to go down (~600rpm, lower than usual)with drops bellow ~300. i have no cel/error. what could it be?
thanks
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Old 11-25-2011, 05:31 AM   #2
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Default Re: idle problem after over rev

Do you hear a knocking noise?
How do you run out of oil? Poor maintenance?
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Old 11-25-2011, 05:54 AM   #3
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Default Re: idle problem after over rev

after the miss shift, oil light turned on and engine sounded really bad. i checked the oil level and it was very low (before over rev oil level was fine).
there is a small knocking noise, but it sounds more it from the exhaust. i feel small vibrations inside the car like shakings but don't know if it's because the low idle.
the engine pulls ok, vtec feels normal, just the issue with the idle behavior
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Old 11-25-2011, 06:12 AM   #4
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Default Re: idle problem after over rev

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Originally Posted by maharvey View Post
after the miss shift, oil light turned on and engine sounded really bad. i checked the oil level and it was very low (before over rev oil level was fine).
there is a small knocking noise, but it sounds more it from the exhaust. i feel small vibrations inside the car like shakings but don't know if it's because the low idle.
the engine pulls ok, vtec feels normal, just the issue with the idle behavior
gonna need another engine!!
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Old 11-25-2011, 07:47 AM   #5
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Default Re: idle problem after over rev

Might of spun a bearing?
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Old 11-25-2011, 07:59 AM   #6
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Default Re: idle problem after over rev

Sounds like it.
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Old 11-25-2011, 08:17 AM   #7
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Default Re: idle problem after over rev

or u might have some bent valves
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Old 11-25-2011, 09:05 AM   #8
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Default Re: idle problem after over rev

how can i check if valves are bent without removing the head? loss of compression or something?
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Old 11-25-2011, 02:40 PM   #9
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Default Re: idle problem after over rev

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how can i check if valves are bent without removing the head? loss of compression or something?

Do a compression test.
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Old 11-25-2011, 07:06 PM   #10
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Default Re: idle problem after over rev

loss of oil pressure right after the over rev indicates a spun bearing, the bearing surface would have been destroyed increasing oil clearance and causing the oil pressure drop. I don't see bent valves causing the oil pressure drop, pull the pan and you will probably find metal.
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Old 11-26-2011, 12:34 AM   #11
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Default Re: idle problem after over rev

when i let the oil out didn't see any metal in it. i'll do a commpression test.
thanks guys. in case of spun bearing, just replace the bearings or could it be the crankshaft too?
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Old 11-26-2011, 07:29 AM   #12
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Default Re: idle problem after over rev

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when i let the oil out didn't see any metal in it. i'll do a commpression test.
thanks guys. in case of spun bearing, just replace the bearings or could it be the crankshaft too?
if you spun a bearing, the engine needs to come apart, it needs to go in an engine stand and be turned upside down so the crankshaft can be removed, then all the journals on the crank need to be checked, you don't replace a bearing, you replace them in a set, I've heard of people replacing one, but thats a really half *** way to fix things.
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Old 11-26-2011, 08:31 AM   #13
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Default Re: idle problem after over rev

usually once u spin a rod bearing its hard to just throw bearings in and think everything is ok. ive seen many people do this and then about 3k later the rod is knocking again. you wil need a new bottom end or new crank and bearings to fix it correctly. or have a shop look at your current crank and see if its within spec.
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Old 11-26-2011, 08:49 AM   #14
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Default Re: idle problem after over rev

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or u might have some bent valves
If you bent valves. The engine would be running very poorly, if running at all.
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Old 11-26-2011, 11:20 AM   #15
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Default Re: idle problem after over rev

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usually once u spin a rod bearing its hard to just throw bearings in and think everything is ok. ive seen many people do this and then about 3k later the rod is knocking again. you wil need a new bottom end or new crank and bearings to fix it correctly. or have a shop look at your current crank and see if its within spec.
the rods might be ok but the only way to check is to remove them and check everything, if you haven't been driving it , the damage might be contained to the bearing shells, if you hav e damaged rod journals and a damaged crank on a stock Honda block, you are better off finding a used one,preferably from a wreck, then you know it was running
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Old 11-27-2011, 02:09 AM   #16
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Default Re: idle problem after over rev

as a said the engine is running quite well, only at idle i hear a small knock which seems to come more from the exhaust (if i cover the muffler with my hand the engine sounds better, smoother, no knocking like). i hoped i don't have to take the engine apart, but i guess i'll have to do it. is there any risk driving the car as it is now?
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Old 11-27-2011, 02:34 AM   #17
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Default Re: idle problem after over rev

If the noise gets quieter when you cover the exhaust it might be a bent exhaust valve. Either way something went wrong and your gonna need to rebuild. If your gonna put new bearing in your going to have to pull them all and take the crank in to get turned. And your gonna want to make sure you didnt burn up your rings. So you might as well just rebuild the whole thing. So your gonna have to take the head off regardless. Long story short, you had a stroke of bad luck thats started with that missed shift.
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125m, b16, civic, crank, damage, engine, fit, honda, idle, jumps, low, overrev, problem, rev, reving, rod, si

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