Technical High revs at start up

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Technical High revs at start up

chrisb7777

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Hi guys

I have mentioned this before but its getting worse now as the cold weather has come upon us and I have just fitted a new engine so i don't want to damage it!

On a completely cold start the car will rev up to and sometime beyond 3k for about 5 seconds before settling down to its normal 1200 rpm cold idle. Surly this isnt normal? Its certainly unnecessary!

Im stuck on what to do, i almost feel like holding the clutch on in gear until it settles to keep the revs down.

The car idles perfect at all other times even when cold. I cant remember if it has always done this but it has been at least a year and gets worse in the winter months. In the summer it will only go up to 2-2.5k

Any help will be much appreciated

Chris
 
Surely there should be a high idle when cold? It seems totally normal at 1200 and the revs slow drop to 850 as the temperature rises, just like any other fuel injected car?
 
Haha yea defineatly!

Could it be to do with the ecu not learning the idle parameters? Also could it be to do with the fact I have a 32mm tb installed?

Since the issue started iv been through different temp senders, intake gasket and sensor and a new engine but no change
 
Throttle returns nicly and the throttle cable has about 1/8 inch free play. I have checked all vacuum pipes numerous times, replaced the rocker cover gasket and all other paper gaskets.

There is the fresh air pipe that feeds off the pcv, why is this needed?

I'm not convinced its a air leak as it would do it every time not just cold starts and gets worse in colder weather
 
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It sounds like an Air leak to me as well... excess air is one of the few things that will let an engine rev that much.

Have you tried a different throttle body maybe to see if that helps,?

You could also have something wrong with the idle air controller. (But it really does sound like an air leak)

you could also have a look inside the TB to see that the butterfly is actually fully closed when the throttle is closed.
 
On cold start, fuel mix should be very rich. Your symptome suggest that it's lean.

I still think air leak, but if you have another TB you might swap over the air temperature sensor, or try another engine temp sensor.

Air leaks can be buggers to find, just stick at it.

You might try physically (gently!) shutting the butterfly while someone else cranks the car (I'm thinking sticky throttle cable, here). Or even disconnect the throttle cable.
 
It is way to controlled to be a vaccum leak, vaccum leaks wouldnt change depending on outside temperature, nor would the computer be able to adjust it back down to normal idle from that high especially without surging.


The pipe the is teed into the pipe coming out of the rocker cover and intake
 
It is way to controlled to be a vaccum leak, vaccum leaks wouldnt change depending on outside temperature, nor would the computer be able to adjust it back down to normal idle from that high especially without surging.



The pipe the is teed into the pipe coming out of the rocker cover and intake

Well, a vacuum leak is, by definition, an air leak..........

From memory, the small diameter T can be blocked off at the TB (run a better bit of pipe to the airbox). But if running standard airbox, better replace.
 
On cold start, fuel mix should be very rich. Your symptome suggest that it's lean.

I still think air leak, but if you have another TB you might swap over the air temperature sensor, or try another engine temp sensor.

Air leaks can be buggers to find, just stick at it.

You might try physically (gently!) shutting the butterfly while someone else cranks the car (I'm thinking sticky throttle cable, here). Or even disconnect the throttle cable.

Yes i think it is running lean at 3k until it returns to normal.

I do have a spare tb to play with, ill swap over the air temp sensors

I have started the car without the throttle cable attached yet no difference, do you think someone could have messed with the throttle stop screw?

I do have the cable to connect the car to the laptop, do you think any of the data it gives off would be any use?

Thanks for your help so far! Air leaks are annoying!!
 
The pipe the is teed into the pipe coming out of the rocker cover and intake
and is it connected to the throttle-body?

It is part of the crank-case breather system. Depending oh throttle butterfly position it either pulls through the small pipe below the butterfly (when it is closed) or through the big pipe that T's into the main intake (when the butterfly is open).

So, is that small pipe connected?
 
Right ill give it a good soak later just incase, yes it is connected up.

Are the iac motors the same for the 30 and 32mm tbs? I think i replaced it a couple of years ago but cant remember if that was on the original tb or not

I seem to remember seeing two different types?
 
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