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Idle speed altering when fans cut in
#1
Just curious about this one-when the cars fully warmed up and ticking over at +-950 rpm (it seems happy at this tickover speed), when the fans cut in the rpm drops by about 200- alternators output checked and still at 13.5 ish volts, fans switch off and idle speed goes back to normal, it's always been like this, and yes, I've checked for air& vacuum leaks but none anywhere. Thoughts, anyone?
#10556 'Ol Stainless' running surprisingly well,Audi A5 2.0T Quattro smug as usual,Wenault Slaguna stationary for the mo',the R.V.Enterprise clocking the U.K.miles up,new fleet addition-Jessica the Daewoo Matiz,silly but 55mpg....!
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#2
When you first start the car, does it rev to about 2000 and immediately drop to idle, and does the idle steadily increase from a cold start?
Martin Gutkowski
DeLorean Cars
http://www.delorean.co.uk
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#3
After going to around 2000 rpm It drops straight down to about 850 ish rpm, and stays there until its fully warmed up- doesn't cut out but idles speed goes up a little to around the 900 mark.
#10556 'Ol Stainless' running surprisingly well,Audi A5 2.0T Quattro smug as usual,Wenault Slaguna stationary for the mo',the R.V.Enterprise clocking the U.K.miles up,new fleet addition-Jessica the Daewoo Matiz,silly but 55mpg....!
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#4
Are the brass screws backed out at all? Is the throttle closing properly? Sounds like the idle system is working but you have some air bypassing the throttles.
Martin Gutkowski
DeLorean Cars
http://www.delorean.co.uk
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#5
No, all three screws are all the way in, I stripped and cleaned the throttle body a while back, no discernible wear at all (38k), all manifold gaskets replaced at the same time, replaced the V.O.D pipes also while checked the vacuum pipes to the heater valve and servo, all good and tight. I always adjust the throttle with the accelerator connection removed, can't think where air could be getting in, but a good pointer-I'll use soapy water on the connections and see what happens, thanks
#10556 'Ol Stainless' running surprisingly well,Audi A5 2.0T Quattro smug as usual,Wenault Slaguna stationary for the mo',the R.V.Enterprise clocking the U.K.miles up,new fleet addition-Jessica the Daewoo Matiz,silly but 55mpg....!
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#6
bjbrownie Wrote:It drops straight down to about 850 ish rpm, and stays there until its fully warmed up- doesn't cut out but idles speed goes up a little to around the 900 mark

...and I would bet a good 50p that when your fans kick in, it drops back down to 850.

In other words, the idle system is fully closed and the engine is idling on a leak of air (not necessarily a vacuum leak) when the engine is hot - enough air to bring it up to 900rpm with no other load. As soon as you give it more load, like from the alternator, the revs drop to 850 at which point the idle system catches it.
Martin Gutkowski
DeLorean Cars
http://www.delorean.co.uk
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#7
my 'normal' cars do this, on my old Omega for instance, if you put the heated rear window on (which
also heated the mirrors), it would increase load on the electrical system and you'd hear the engine note
change and the idle revs drop ever so slightly.
Claire  - DOC-UK Treasurer
1981/W DeLorean DMC-12 'Flopsy' - #2292 - resting due to block rot 
1989/G Vauxhall Cavalier 1.6L 5dr "Guinney" -
1995/N Renault Espace RT Alize 2.1TD "Jaffa the Bus"
DOC170
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#8
I'll give it a looking at very soon, it's getting warmer and drier! Cant think of where air could be bypassing the throttles but squirting some soapy liquid may reveal an air leak (hopefully )!
#10556 'Ol Stainless' running surprisingly well,Audi A5 2.0T Quattro smug as usual,Wenault Slaguna stationary for the mo',the R.V.Enterprise clocking the U.K.miles up,new fleet addition-Jessica the Daewoo Matiz,silly but 55mpg....!
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#9
bjbrownie Wrote:it's getting warmer

you've not seen next weeks weather forecast then....
Claire  - DOC-UK Treasurer
1981/W DeLorean DMC-12 'Flopsy' - #2292 - resting due to block rot 
1989/G Vauxhall Cavalier 1.6L 5dr "Guinney" -
1995/N Renault Espace RT Alize 2.1TD "Jaffa the Bus"
DOC170
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#10
I did Claire, never trust the BBC............
#10556 'Ol Stainless' running surprisingly well,Audi A5 2.0T Quattro smug as usual,Wenault Slaguna stationary for the mo',the R.V.Enterprise clocking the U.K.miles up,new fleet addition-Jessica the Daewoo Matiz,silly but 55mpg....!
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#11
bjbrownie Wrote:I did Claire, never trust the BBC............

:lol: :lol: :lol: :lol:

How can you tell when a weatherman is lying?

His lips are moving :wink:
Claire  - DOC-UK Treasurer
1981/W DeLorean DMC-12 'Flopsy' - #2292 - resting due to block rot 
1989/G Vauxhall Cavalier 1.6L 5dr "Guinney" -
1995/N Renault Espace RT Alize 2.1TD "Jaffa the Bus"
DOC170
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