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Why does my engine rev up and down continuously when cold?


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12 replies to this topic

#1
TOPDOGDC5

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when i start my car after a while of non use, it revs up and down for few minutes then goes back to normal rev. can someone please help me sort out my problem as it is worrying me so much. Quick help would be appriciated. my car is a 2001 INTEGRA DC5 JDM with 53k on the clock

Thanks

#2
The Lum

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Mine does exactly the same. I assume it starts high (about 1.8-2k) then drops slowly? If so I would say it's just the ecu realising the engine is cold and trying to heat the oil etc up to working temp as soon as possible.

If it's very sporadic though and jumps right up then then up then down etc etc I would say that's exactly what it is.

#3
-Woody-

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Its just the the automatic choke??? Depends how eratic it is, mine can rev 0.5-2k for a minute or so.

#4
TOPDOGDC5

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Yeah thats it, Spot on. you have stolen my words! Any idea how to fix this problem? Is it an easy fix or hard one( money wise too) ??? How are you looking to fix this in your car? Do you have a DC5 too


Mine does exactly the same. I assume it starts high (about 1.8-2k) then drops slowly? If so I would say it's just the ecu realising the engine is cold and trying to heat the oil etc up to working temp as soon as possible.

If it's very sporadic though and jumps right up then then up then down etc etc I would say that's exactly what it is.



#5
TOPDOGDC5

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I forgot to mention the Engine management light came on as well

#6
rodney

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My car is a 2001 INTEGRA DC5 JDM


All DC5's are JDM mate.
52' CW DC5

#7
oregato

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Yeah thats it, Spot on. you have stolen my words! Any idea how to fix this problem? Is it an easy fix or hard one( money wise too) ??? How are you looking to fix this in your car? Do you have a DC5 too


Mine does exactly the same. I assume it starts high (about 1.8-2k) then drops slowly? If so I would say it's just the ecu realising the engine is cold and trying to heat the oil etc up to working temp as soon as possible.

If it's very sporadic though and jumps right up then then up then down etc etc I would say that's exactly what it is.


Mine stays at the 2k rpm mark until warm, it drops down gradually and then sits below 1k at 800 rpm or so.

If yours is doing the same then its fine.

If it's jumping up and down like mad, then you may have a problem.

Get the engine management light checked on it.

#8
tricker_luke

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Don't pay for a management light scan, do it yourself

http://www.k-series....ument.php?id=37

Simply linking pins 4 and 9, then turn the ignition on. Count the number of flashes and they represent the fault code. It's all on that link I added.

#9
steellam

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It is usually the idle air control valve which is bolted on the underside of the throttle body, its easier to remove the full unit to get too it., but you have to take care not to damage the gasket between the inlet and throttle body.

It is a little rotary valve that is operated by a magnet, it gets crapped up and can take a couple of tries to get clean, i have used carb cleaner and WD40 in the past.

Hope that helps !

#10
shauny

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Mine does the same,Seems alot of dc5's do this.I didnt think it was normal but since so many people have the same problem it must be ok.

#11
VT-Doo

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The cold idle on most Honda's I've driven have a higher than "normal" RPM. The DC5 has a fast idle of 1,800+(-) 200RPM.
As the temperature of the the coolant increases the idle decreases and settles at 700+(-)50RPM.

A surging idle (hunting) is caused by a vacuum leak. If all you hoses are ok and not split or disconnected then the leak will be between the cylinder head and the throttle body.

However, you say your idle surges when the engine is cold and that your EML is on. To me this sounds like a Primary O2 Sensor failure.
When the O2 sensor fails the engine will run rich (bare in mind the standard ECU runs rich as standard).
When you start the car from cold with a failed O2 Sensor it is possible that your engine is over fueling to an extent that a hunting effect is produced.

I'm not going to get into it too much but I had to remove 20% cranking fuel from my K-Pro in order to stop this which also enabled my engine to fire up a lot faster.
Ian



Premium White Pearl Honda CR-Z GT.

#12
C&S Evo7

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If the revs are high (1200-1500 ish) then drop to normal -900 ish then i wouldnt worry, if they hunt up and down then the Idle air control valve is the likely cause, if the revs remain high then look for a vacuum leak or at the iacv but It is very common on a k20a to have the hunting problem, it will be the IACV for sure. (90% of the time)

it can be removed and cleaned which works sometimes, but often it needs to be replaced, sadly that means the whole throttle body as the parts are not available separately, this used to be around £400 but i'm sure i read that recently one had been bought from Dave at Steels for £200.

when the car is idling the throttle butterfly is completely closed so to supply the engine with enough air to allow it to run you need to bypass the butterfly, there is a small hole just infront of and just behind the butterfly and connecting the two holes is he idle air control valve.

this is controled by a small motor which allows the actual amount of air bypassing to be adjusted, when its cold it needs more, when the a/c comes on it needs more, when you switch the lights on it needs more etc, when switched off the required air volume is reduced so the idle can remain constant.

when the valve gets dirty it gets sticky and doesnt work accuratly or at all, so the ecu tells it to be at a position (which it cant do) so the revs raise, the rpm raise is detected and the ecu tries to correct by trying to move the motor again which it cant so the revs drop, and it continues like this in a vicious circle.

To remove the throttle body as previously mentioned you need to be careful of the gasket (its wise to get a spare from Honda just incase it gets damaged before you start) once off the valve can be got at better for removal, you might need a torx bit from memory it is best to use carb cleaner rather than thinners etc . Its not a complicated job at all.

DO NOT be tempted to put 12v on the pug to see if it works as it can be easily damaged

#13
TheBigRedSmoke

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Brand new idle control valve was approx £125 delivered from Dave at Steels.

Fitted mine this weekend and car now runs perfectly.
NHB DC5, Titanium & C-Pack, HKS, Jazma,Volk GT