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Author Topic: High revs at cold start  (Read 645 times)

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Muroman

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High revs at cold start
« on: 12 October 2018, 06:27:27 »

Hey,

I've been postponing this question a bit but now it's the time to ask it  :)

Car -99 automatic X30XE

I changed my air filter to K&N filter 2 years ago and after that the engine revs anything between 2000-3000rpm depending on temperature when starting it cold.
The K&N filter is similar to the original filter so no modifications have been made. Only that the K&N filter might have better air flow.

In time of 2 years the plenum and other intake parts has been uninstalled many times so I think there isn't any leaks in intake parts as this has been ever since the air filter change.

I'm not even scared of the 2000 but the 3000 is too much? The rpms drop down to ~1100 after 2-3secs and then after 30-60sec to 800 and when fully warmed 450-500. Before the filter change rpms started from 1200-1500.
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Doctor Gollum

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Re: High revs at cold start
« Reply #1 on: 12 October 2018, 08:19:18 »

First thought is a failing a MAF, too much air would see an increase in fuel and therefore rpm. Does it do it with the MAF unplugged? If no, then that's that...

It might also be a sign of a failing ecu temperature sensor, unless you have had some seriously cold mornings already... Does it start OK when hot? If no, then this is potentially a cause...

Other places to look are sticking throttle body or a small air leak which closes up as the engine warms through.

Live data should help pin point the culprit :y

The ecu uses this to determine fuelling and when it fails the ecu presumes that it is - 40c and overfuels the engine.  This is also why the engine runs rich when cold.
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Muroman

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Re: High revs at cold start
« Reply #2 on: 12 October 2018, 13:53:06 »

MAF broke a half year ago, didn't notice difference on those so I think that it isn't.
https://www.omegaowners.com/forum/index.php?topic=141823

Temp sensor (both) changed 3 years ago while head gasket change. So that is low possibility.

Throttle body and all those intake parts, should be very clean as nowdays I have EGR blocked and even oil fumes are going in separate reservoir and from there to open-air by another filter.

Live data would be the first then, It's just that my omega is very hard to read as none of the readers that I have tested haven't worked....
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zirk

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Re: High revs at cold start
« Reply #3 on: 12 October 2018, 15:14:16 »

Did you Oil or over Oil the K%N Filter when when fitted? if so could be oily MAF.

I use K%N but always use them dry, unless your going on a Dakar Rally or live somewhere very Sandy or Dusty.
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dave the builder

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Re: High revs at cold start
« Reply #4 on: 12 October 2018, 16:10:19 »

MAF broke a half year ago, didn't notice difference on those so I think that it isn't.
https://www.omegaowners.com/forum/index.php?topic=141823

Temp sensor (both) changed 3 years ago while head gasket change. So that is low possibility.

Throttle body and all those intake parts, should be very clean as nowdays I have EGR blocked and even oil fumes are going in separate reservoir and from there to open-air by another filter.

Live data would be the first then, It's just that my omega is very hard to read as none of the readers that I have tested haven't worked....
ECU temperature sensors can fail any time and are a common fault on many vauxhalls, live data will be helpful

do you have a valve in place or other method of stopping your oil catch can / reservoir from sucking un-metered air as the oil fumes would have been recirculated for combustion via intake (is the re circulation port blanked or sucking air   :-\ )

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Nick W

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Re: High revs at cold start
« Reply #5 on: 12 October 2018, 17:07:49 »

Did you Oil or over Oil the K%N Filter when when fitted? if so could be oily MAF.

I use K%N but always use them dry, unless your going on a Dakar Rally or live somewhere very Sandy or Dusty.


It's the oil that makes a K&N an effective filter. No oil and it's just a large piece of cotton.
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Re: High revs at cold start
« Reply #6 on: 12 October 2018, 18:36:35 »

And also what shags the MAF, so best to leave the standard filter in place.
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Muroman

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Re: High revs at cold start
« Reply #7 on: 12 October 2018, 22:57:21 »

I use oil in the K&N filter but only the minimum I think. And yes I agree that the K&N filter will probably be bad for the MAF but yeah, it should still last long time.

Yes, I have those oil fume re-circulation pipes blocked on the plenum so no air can rush in.

Would it be that the ECU just can't understand how much and clean air the engine is getting and therefore tries too much and that raises the rpms?
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Andy H

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Re: High revs at cold start
« Reply #8 on: 12 October 2018, 23:20:37 »

Could it be the idle air control valve (IAC)?

Is yours working OK? Is it a secure air tight fit in the plenum?
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Muroman

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Re: High revs at cold start
« Reply #9 on: 16 October 2018, 06:32:39 »

Idle control valve, I guess it's working fine as there isn't any stall issues and it changes rpms smoothly for example when warming up and it's clean for sure too but you got me thinking that it isn't as tight as it has been. Any fixes or should I get new rubber part for that?
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Re: High revs at cold start
« Reply #10 on: 16 October 2018, 09:27:25 »

Check the seal carefully first, but if you can get it, it's probably a good place to start :y
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Muroman

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Re: High revs at cold start
« Reply #11 on: 24 October 2018, 06:38:24 »

Well I re-installed the ICV, re-installed intake from plenum to air filter, cleaned air filter.

Only problem I found was that one of the pipe clamps was loose and when I  tried to tighten it again it wouldn't go tight as it only turns around if you know what I mean. But yeah bought new clamp.

Started and it almost stalled the first time and now highest revs in a week has been about 1800rpms. So I guess it was some leak after all, it was just hard time to believe as the intake has been re-installed so many times and it hasn't been fixed before....

Thanks again fellow omegaowners :)
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Fuse 19

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Re: High revs at cold start
« Reply #12 on: 24 October 2018, 10:15:02 »

For info, MAF has no impact on idle rpm, that is based purely on rpm, hotel load (to an extent) and coolant temperature.

So rpm is high always going to be either a result of throttle valve not closing fully, idle valve sticking or un-metered air getting in.
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Muroman

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Re: High revs at cold start
« Reply #13 on: 24 October 2018, 12:17:32 »

For info, MAF has no impact on idle rpm, that is based purely on rpm, hotel load (to an extent) and coolant temperature.

So rpm is high always going to be either a result of throttle valve not closing fully, idle valve sticking or un-metered air getting in.

Good to know!

Is it possible that a leak in exhaust manifold or other parts of exhaust could impact on the rpms? Or is that only going to change how much fuel goes in?
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Re: High revs at cold start
« Reply #14 on: 24 October 2018, 12:58:02 »

For info, MAF has no impact on idle rpm, that is based purely on rpm, hotel load (to an extent) and coolant temperature.

So rpm is high always going to be either a result of throttle valve not closing fully, idle valve sticking or un-metered air getting in.

Good to know!

Is it possible that a leak in exhaust manifold or other parts of exhaust could impact on the rpms? Or is that only going to change how much fuel goes in?

It will only impact the fuel mix by confusing the O2 sensors  :y
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TheBoy

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Re: High revs at cold start
« Reply #15 on: 24 October 2018, 17:05:37 »

I suspect this mystery is solved by the revelation that the breathers are open to atmosphere :)
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Muroman

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Re: High revs at cold start
« Reply #16 on: 25 October 2018, 05:46:14 »

I suspect this mystery is solved by the revelation that the breathers are open to atmosphere :)

Well, only the small one but yeah
« Last Edit: 25 October 2018, 05:51:38 by Muroman »
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Muroman

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Re: High revs at cold start
« Reply #17 on: 28 October 2018, 20:18:37 »

Breather pipe did not change a thing, still reving 2000ish
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