strange idling

Site Subscriber Joined: 24 Apr 2004 Posts: 318

not a problem as such but just puzzles me:

Picture the scene:
sitting in traffic on a slight downhill,
When the car is stationary and it idles as normat 750rpm-ish
let off the brake to coast, havn't touched the accelerator or clutch & still in neutral, but as the car starts to move the revs rise to about 1200, stop again and the revs drop back to 750.

always does this i.e. always revs higher when coasting than when stationary.

As I said it doesn't particlarly bother me but it puzzling.

any ideas?

Oh & it's a 1.8spi

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

road speed sensor detecting motion raises the idle speed to prevent stalling on over run etc.

1200rpm is bang on to where it should rise to. Yours is 1 of th efew that sounds like it works as its supposed to!

Site Subscriber Joined: 24 Apr 2004 Posts: 318

woo hoo - something that works properly Shocked

This is my first injection, fancy electronicy car I've had (my first car that wasn't a mini!) so these things are strange to me!

Cheers Chris I'll rest easy tonight knowing that!

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

explanation as to why.

Drivign along coming to a junction doing 50, the car has been coasting out of gear for a bit thus over run fuel shut off is engaged, you dip the clutch, the revs drop rapidly, over run shut off disengages and slowly brings the revs down to idle when you stop.

if the road speed sensor etc is dodgy then you coast along dip the clutch and the ECU doesn't know the cars actually moving, revs drop to quick for the injectors etc to come back into action engine cuts out.

Site Subscriber Joined: 24 Apr 2004 Posts: 318

those cunning french - what ever will they think of next!

..ok so I imagain all cars have this but the joke wouldn't have worked as well Embarassed

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yep all injection cars are like this.

Saves fuel, on overrun the injectors stop injecting totally, so the engines just freewheeling basically.

Spammer Joined: 27 Jul 2004 Posts: 5717

my 1.8 SPI works exactly the same way ,i used to think it was a problem too but then found out thats the way they are meant to work .

Level 8 User Joined: 02 Dec 2004 Posts: 263

ok, the third 1.8 SPI owner cant agree Crying or Very sad

Mine has begun to idle very funky. When stationary it runs low and suddenly high, low again, high again......goes on like this until i drive away. Yesterday when i was going home from work i started the car and let it heat. Went in and finished work. When i got out and started to sweep the snow off it, i heard the chronic poor idling and suddenly when half sweeping was done, it just died. Also i had to jump start it since the battery is #$"%#$%.
Any ideas to the poor idling? I've noticed ideas about CTS and something else....Does it have nothing to do with oxygen sensor or anything?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

the revs going up and down will be the lambda/oxygen sensor. If you look under the car you will see the lambda sensors conector on the back of the subframe. Unplug it and see if the idle sorts itself out.

I have a dodgy lambda sensor I just can never bothered replacingit so the idle only sometimes goes up and down. However it was made very bad when the throttle position sensors plug wasn't clicked home properly.

Spammer Joined: 27 Jul 2004 Posts: 5717

CTS is really easy to remove you might as well check and clean it too. just note a fair amount of water will come out just stick a rubber or a vine cork as soon as you unscrew the CTS . clean the metal head and put back in .
off topic i know but can you also tell how the lambda is affected by decat or is it affected at all when a decat pipe is put on???
cheers

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

its not affected in any way

Level 8 User Joined: 02 Dec 2004 Posts: 263

Is this the CTS?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

yep thats the CTS

Level 8 User Joined: 02 Dec 2004 Posts: 263

Chris H wrote:

If you look under the car you will see the lambda sensors conector on the back of the subframe. Unplug it and see if the idle sorts itself out.

Any better guidence for a newbie ? Smile

On the location i mean....

Mr Quoter-vator Joined: 16 Feb 2004 Posts: 7405

the wires will be leading to the exhaust at some point

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

in front of the gearlever under the car is the lambda sensor, follow th ewires forward to the engine subframe, you can't miss it.

Spammer Joined: 27 Jul 2004 Posts: 5717

watch you dont snap the bolt on the CTS while taking out .i have done it so you would not.