Varying High Idle, Increasing To 3000Rpm When Getting Hot

[johnhenry 20]

Afternoon all

 

Have just experienced this rather annoying fault.

 

Idle - great 900rpm at normal running temp

 

sat in a que for about 10 minutes, the temp is creeping up, as the fans start to come on 'low' the idle is rising, but seemingly only when

I touch the throttle :S - I thought possibly sticking to something, but that changed as it got hotter.

 

temp now getting warm in the traffic, idle is now up around 3000rpm, and no matter what I do and try, it varying from 2700 on the button and 3000 on the button,

 

I switch the car off and on, and the idle is still there high.

 

Luckily i get through the Severn Toll que, cool it down quickly in the free moving motorway, and boom the idles perfect again, 900pm on the money!

 

electrical fault? or investigate a sticky throttle cable when warm?

 

Cheers

John

 

[PhilNW 40]

Sound similar to my recent problem - try the temp sensor which tells the ecu what the water temp is.

[johnhenry 20]

Sound similar to my recent problem - try the temp sensor which tells the ecu what the water temp is.

 

Good job there's a spare new one in the garage! seems to make sense tbh!

[johnhenry 20]

bit of an odd one, but would an over tensed throttle cable at the throttle body cause this at all?

[dcc 855]

Logically speaking john, ofcourse! It wouldnt allow the throttle butterfly to close properly.

 

is it on a 8v xu or a 16v?

[DamirGTI 325]

When the revs start increasing try to pinch the SAD hose .. and see if the revs will droop .

 

D

[johnhenry 20]

Thanks all!

Ive slackened off the throttle cable clip, see if that makes a difference,

The weathers dire - so I can't change the ECU temp sensor over yet

will check SAD - Have had SAD problems in the past, this feels different, but will check none the less

[DamirGTI 325]

Yes the SAD usually , when the heater element is not receiving voltage to fully close it , rises the idle speed with the coolant temp. drooping .. so opposite from this what is happening on yours , but check anyway .

 

One is sure it's something temp. related , as it changes proportionally with the coolant temp. rise and droop - could be ECU temp sensor as said ..

 

Is yours Motronic with an lambda sensor ?

 

D

[johnhenry 20]

will change the ECU temp sensor tomorrow morning as I'm driving down to the devon in the afternoon, will give it chance to get hot somewhere probably!

 

Damir; it is jetronic, no lambda

[unariciflocos 49 1 Cars]

It's unlikely that the engine will go up to 3k without additional air, my money is on the SAD.

[johnhenry 20]

swapped out the ECU temp sensor (blue) , and slackened off the throttle clip, got it pretty hot in traffic through plymouth the other day, no signs of the issue.

 

may well be valid about the SAD, but isn't this controlled by the ECU coolant Temp sensor (blue), car idles high as the SAD is open when cold starts in the morning, that is working, possibly getting an iffy signal and doing other stuff from there.

 

the real test will be the Severn Bridge toll que in couple of days!

[DamirGTI 325]

The thing with the SAD is that it uses both the temperature of the cooling system (for this very reason it's mounted under the housing where the heater matrix hoses join) and built in heater element .. to be able to close bimetallic disc completely after cold start/warm up period it needs both - exposure to the coolant temp. and voltage supply to the heater element ..

 

I've had few occasions where the plug/connector for the heater element has disconnected itself from the SAD heater cause of vibrations (the clip was missing) and another was wire breakdown/no voltage supply trough the wiring to the heater thus the engine had good stable idle with the engine/coolant hot in stop-and-go town driving , but as soon as the coolant temp. dropped while moving off the town traffic driving and going on the straight road/motorway the idle speed stared rising to 1200-1500-2000rpm. so it reacted per exposure to the coolant temp. without heater in function to add closing as the coolant temp. drooped down the bimetallic disc started to open up again .

 

This is why i initially thought it could maybe be SAD issue , but as said , despite fact that from your description was actually opposite - not bad idea to check anyway as it's easy ..

 

If it's now fine after ECU temp. replacement , suppose it was that then ...

 

D