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Author Topic: Engine runs smoother when cold  (Read 2772 times)

Offline MacBain

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Engine runs smoother when cold
« on: 30 May 2007, 15:19 »
Seems like my engine runs better/smoother when it's cold, but after a few minutes it stutters/jerks more.
It's almost impossible to drive slowly without the car stuttering, it's so incredible sensitive when I lift off the throttle.

I don't have these problems when I start the car up in the morning.
It also idles better at about 1000rpm when cold, after it reaches the normal temprature it idles at about 850-900 rpm, but it seems to idle more roughly.

Any idea on what the problem could be?, would incresing the idle rpm help?


Ps. The car is a 1990 1.8 GL with a rp engine with a mono-jetronic carburator.
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Offline Simpson

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Re: Engine runs smoother when cold
« Reply #1 on: 30 May 2007, 17:28 »
sounds like you need to check vacuum pipes, the reason it revs about 1000 is the choke is coming on when cold. It should be ideling about 850 to 950 revs as a rough guess. Have you checked simple things like leads, plugs etc?  :smiley:
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Offline MacBain

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Re: Engine runs smoother when cold
« Reply #2 on: 30 May 2007, 18:33 »
I've changed all the plugs, wires and distributor cap. I also cleaned the carburator with some carb cleaner.
I don't think there's a vacum leak because I've tried spraying starter spray around all the pipes etc. and the rpm stayed the same.
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Offline mk2mark

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Re: Engine runs smoother when cold
« Reply #3 on: 31 May 2007, 08:51 »
Sounds like the sensitive lift off is a slack throttle cable, you can tighten it on the throttle body.
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Offline rubjonny

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Re: Engine runs smoother when cold
« Reply #4 on: 01 June 2007, 10:50 »
check out the blue temp sender then lambda probe next :)
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Offline MacBain

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Re: Engine runs smoother when cold
« Reply #5 on: 01 June 2007, 12:52 »
I've changed the blue temp sensor.
Is changing the lambda probe difficult to do?

I know my catalysator has been gutted, could this cause anu problems?
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Offline rubjonny

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Re: Engine runs smoother when cold
« Reply #6 on: 01 June 2007, 13:09 »
nah it wont be a problem. lambda isn't hard you unscrew it from the zaust & replace it.  Get a universal bosch one, bit cheaper than a gen vw one!

Quick test you can do is unplug it, if the car runs better then you have a faulty lambda :)
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Offline MacBain

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Re: Engine runs smoother when cold
« Reply #7 on: 01 June 2007, 14:13 »
Where is the lambda plug located?
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Offline rubjonny

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Re: Engine runs smoother when cold
« Reply #8 on: 01 June 2007, 14:32 »
its in the downpipe somewhere, if you follow the exhaust back you'll see the probe sticking out of it, then follow the wiring up to the plug :)
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Offline MacBain

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Re: Engine runs smoother when cold
« Reply #9 on: 01 June 2007, 16:15 »
I think the plug is the one marked in red on the picture (according to the haynes manual).
Can I drive with the lambda unplugged?
Could it cause any harm?
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