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Holding revs

 
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  #1 (permalink)  
Old 20 Oct 2012, 05:41 am
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Default Holding revs

Hi an good morning.
I have a problem on my 2001 car.
When I'm gearing down I don't have enough engine braking.
If I dip an hold the clutch down the revs hold around 1500 then drop to around 1000 then settle down to 800.
So when I want to gear down up to a junction I still need to use the brakes.
This is ok if I am stopping but if the lights change I am in to high a gear and labour the engine or too low a gear a it's jurky.
And it seems as if its not free revving even when stood.
Thanks
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Old 20 Oct 2012, 06:55 am
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Default Re: Holding revs

As a 2001 model, the high mileage (taking a guess here) could affect the throttle body (has it ever been cleaned?). The IAC (Idle Air Controller) could be dirty or malfunctioning or the TPS (Throttle Position Sensor) may need to be replaced.

After saying all that, it could be as simple as a small vacuum leak in any one of the rubber vacuum hoses around the engine compartment.
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Old 20 Oct 2012, 09:51 am
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Default Re: Holding revs

This is also the general case with all cars these days. They are engineered to continue to roll along when you lift your foot from the throttle without much engine braking for polution control reasons. Even though you are lifting your foot, the throttle butterfly is not slamming shut but is being held open or closing much more slowly than the action of the gas pedal.
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Old 20 Oct 2012, 12:47 pm
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Default Re: Holding revs

Using the engine a brake is not the best idea to begin with it is not a "big rig". This practice slams the rings upward and the crankcase pressure places a different wear which on an engine with already substantial miles accelerates its wear. Brakes are made for stopping the vehicle on a car.
Might also be a worn engine? A compression check would tell some of the story. I notice that there seems to be an absence of this on older high mileage PTs when diagnosis many issues around here?
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Last edited by NitroPT; 20 Oct 2012 at 12:52 pm.
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Old 20 Oct 2012, 02:17 pm
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Default Re: Holding revs

Engine braking is an efficient way to slow the car, without dangerous brake overheating.

That's why the owner's manual suggests this practice.


My 2.0 has 286,000 and has always been engine braked / downshifted. When might this procedure cause it to break!

The sky is not falling.
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Old 20 Oct 2012, 02:45 pm
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Default Re: Holding revs

Quote:
Originally Posted by interceptor View Post
Hi an good morning.
I have a problem on my 2001 car.
When I'm gearing down I don't have enough engine braking.
If I dip an hold the clutch down the revs hold around 1500 then drop to around 1000 then settle down to 800.
So when I want to gear down up to a junction I still need to use the brakes.
This is ok if I am stopping but if the lights change I am in to high a gear and labour the engine or too low a gear a it's jurky.
And it seems as if its not free revving even when stood.
Thanks

i never use the brakes. that would drive me nuts.

take off the intake tube. with the car off, step on the gas pedal and release it slowly. then get out and see if you can push the throttleblade closed anymore. maybe the cable is sticking a little, or the return spring on the TB is getting weaker, or it's gummed up and sticking open slightly

you could also take the throttlebody off and clean it, clean the IAC(gently). see it this helps. it's easy/free.

if this doesn't help to fix it, it'll help eliminate possibilities.


if i unplug my TPS sensor it doesn't affect my idle. i'd skip worrying about that.
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Old 20 Oct 2012, 04:32 pm
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Default Re: Holding revs

Quote:
Originally Posted by UptownSport View Post
Engine braking is an efficient way to slow the car, without dangerous brake overheating.
That's why the owner's manual suggests this practice.
My 2.0 has 286,000 and has always been engine braked / downshifted. When might this procedure cause it to break!
The sky is not falling.
Perhaps I should have been more clear with my previous response? Engine braking should be used for critical breaking not as a primary form of braking.

Claims of extreme mileage on engines are rare and seldom does anyone get to see them torn down for inspection reveling there true condition.

Pistons and rings get there lubrication from two sources the fuel and the crankcase oil. When you engine compression brake your eliminated the lubrication from the fuel. In some circumstances you can get an acute lack of lubrication between the piston and running cylinder surface. This can cause small seizures and will increased wear or even cataclysmic engine failure. The small damage can not be ready seen without engine dis-assembly. This unseen damage is located located at the load bearing points between the piston skirt and the cylinder. Under normal engine operation would be found undamaged.

The sky must be falling?

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Old 22 Oct 2012, 03:23 am
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Default Re: Holding revs

Thanks for all the replies.
I under stand where both sides are coming from.
I remember when I went out with my youngest in an old land rover we had and she just depressed the clutch an braked all the way to the junction.
When I was tough to drive? cars only had disks on the front if you where lucky.
Most had drum brakes all round and some with out a servo.
So for me old habits die hard gearing down while de accelerating to match the road speed up to a junction ready to drive though the lights if they change.
And I even do it today in the modern auto flappie paddles thing.
An with my old classic I find it very useful to use the engine braking on steep hill any thing to save the brakes from fading due to heat.
I did not have time to look at the car this weekend as we where busy an now we have rain for at least two days.
At the risk of pushing my luck could any one post a picture with numbered arrows as to where the parts you all refer too.
Thanks in advance.
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Old 22 Oct 2012, 05:57 pm
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Default Re: Holding revs

Fuel isn't a lubricant-
It's a dispersant, it causes wear by washing oil off cylinder walls- That's why engines without thermostats wear so quickly- More fuel condenses on the (relatively) cold cylinder wall.

No matter the condition, an engine that's 18 years old, has near 300,000 miles, over 100 runs at dragstrip and is still nominally running couldn't be condemned by any means.
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