High Idle

[Darren C]

Hi Mike,

Doh! :oops:

I've just got out our mag no 38 (autumn 07) Chris W's article Into the valley of death shows the switch in all its glory!

How the heck do I get to that! (well I know it's probably manifold off job)

I assume its the rear most sensor on the o/s with multiplug not the forward one on just a spade?

I'll take a look tomorrow, just need to muster the inspiration to get in at it!

PS cars a 5 speed manual.

Best regards
D

That spare plug I have is obviously a Red Herring!

[bozzzydmc]

lol

any luck checking your 'butterfly valves' ?

[bozzzydmc]

Darren C Wrote:Hi Mike,

Doh! :oops:

I've just got out our mag no 38 (autumn 07) Chris W's article Into the valley of death shows the switch in all its glory!

How the heck do I get to that! (well I know it's probably manifold off job)

I assume its the rear most sensor on the o/s with multiplug not the forward one on just a spade?

I'll take a look tomorrow, just need to muster the inspiration to get in at it!

PS cars a 5 speed manual.

Best regards
D

That spare plug I have is obviously a Red Herring!

You can actually get to it by laying over the engine and with a torch looking down into the valley... i cant see that being your problem unless your wire has come off it ..


thermal switch

[Darren C]

Not yet Mike,

Hunger got the better of me!

Started work this morning at 5am, so I've had enough for tonight, will be back on it tomorrow evening though. I'll let you know, but my gut feeling is its ECU/electrical, as the RPM wanders very slightly or drops abruptly around 2900-3100.
If it was a mechanical jam I would have thought it would be constant.

Also it wont start when warm? Have to wait 45 mins if shes hot for it to cool down, before she fires?

Best Regards
D

[NickT]

The thermistor is basically like a modern Coolant Temp Sensor. It varies its resistance with temperature.

You can test the circuit from the idle speed plug end WITHOUT having to remove the inlet manifold etc.

Disconnect the White plug from the Black Idle speed ECU that has 4no wires into it.
Set a multimeter to 20kOhm range.

Connect multimeter leads to Black/Yellow wire and the Black/Slate(Dark Grey) wire. They are diagonally opposite each other. Depending on temperature, you should get between 8kOhms and 12kOhms on a cold engine.

If you do then you know that the wiring and thermistor are OK.
If it is open circuit then you need to trace cabling back but usually in this instance the connector plug has fallen from the thermistor.

Another thing to check is the idle motor itself.

Remove black 3 pronged plug from the idle motor (Idle Speed Control Valve ISCV)
Set multimeter to 200 Ohms range.

Connect the red lead to the centre pin.
Connect the black lead to the left hand pin, take a reading.

Connect the read lead to the centre pin.
Connect the black lead to the right hand pin, take a reading,

They should be within 10% of each other.

If one reading is open circuit then you need another ISCV.

Test the ISCV:

Remove black 3 pronged plug from the idle motor (Idle Speed Control Valve ISCV)
Use a 2 amp fused wire from the jump start post and carefully hold it on the centre pin.

Use an earthed wire (connected to inlet manifold is OK) and BRIEFLY (<1second) tap it on one of the outer pins. The ISCV should move fully round and you can hear it tap.

Use the earthed wire and BRIEFLY (<1second) tap it on the other outer pin. The ISCV should move fully round the other way and you can hear it tap.

Keep tapping the outer pins to ensure it is spinning quickly.
If it doesn't move then it is stuck in the open position causing your high idle.

I have a spare ECU I could post to you that I know fully works that you can test on the car. Send me a PM if required.

Hope this helps.

Nick.

[NickT]

Further to previous post,

Remove White Plug (that has 4 cables in) from Black Idle Speed ECU.

Set the multimeter to voltage 20v scale.
Connect Red cable to Jump Start Post.
Connect Black cable to Black/Green cable.
With throttle plate closed you should get >12v
With throttle plate open you should get no voltage reading.
If you don't get this then the wiring to/ from the switch is not good or the in-lone diode (under the ECU under the metal bracket) is duff or has a wire falle/ pulled off.

Remove White Plug (that has 5 cables in) from Black Idle Speed ECU.

Check that the Green cable has >12v with the ignition key in position 2
Check that the Black Cable is a good earth.

Enjoy

Nick.

[Darren C]

Hi Nick,

Just got in from the garage. With my best mirror on a stick and a bright light I just can't see the Thermister. Neither I doubt could a Harley Street Gynaecologist!
Can however see the cable disapearing into the abyss, it feels as if its connected because I can give it a tug and it feels conected.

Used my workshop manual to see that the pins 9 & 11 on the ECU lead to the thermister.

Tested these at the ECU plug BS & BY

Multimeter however shows open circuit!

Problem is I have a DMC Tech manual for the electrics also, and it shows item 3 in the wiring diagram as a Thermal Trip? with a switch symbol, not a variable resistor symbol?

Which is right? as I dont want to strip off the intake manifold in vain.

Do you or anyone have a good spare thermister I could hot wire into the ECU plug and see if the idle settles on start before I pull it all apart?

Best Regards
Darren

PS did check the butterfly and linkage all fine.

[Tourettes Tony]

i do have a spare thermister il have a look later TT

[NickT]

Darren C Wrote:Hi Nick,

Just got in from the garage. With my best mirror on a stick and a bright light I just can't see the Thermister. Neither I doubt could a Harley Street Gynaecologist!
Can however see the cable disapearing into the abyss, it feels as if its connected because I can give it a tug and it feels conected.

Used my workshop manual to see that the pins 9 & 11 on the ECU lead to the thermister.

Tested these at the ECU plug BS & BY

Multimeter however shows open circuit!

Problem is I have a DMC Tech manual for the electrics also, and it shows item 3 in the wiring diagram as a Thermal Trip? with a switch symbol, not a variable resistor symbol?

Which is right? as I dont want to strip off the intake manifold in vain.

Do you or anyone have a good spare thermister I could hot wire into the ECU plug and see if the idle settles on start before I pull it all apart?

Best Regards
Darren

PS did check the butterfly and linkage all fine.

It's a thermistor. Don't take the symbols as absolute, more of a 'guide' :

Approx 20k to 30k Ohms at 0 Deg
Approx 10k-12k Ohms at 20 Deg C
Approx 3k to 5k Ohms engine warmed up

Try sticking a 10k Resistor (1.2 Watt) in socket pins 9 and 11 to see if the idle speed comes down.

Good luck, let us know how it goes.

NickT.

[Darren C]

Hi All,

Definately the thermister, put a 10Kohm resistor in pins 9 & 11 on idle ECU, and she purrs like a kitten,.

Thanks everyone for your help. Especially Nick T, for the resistor trick.

13p at Maplins!

Just need to change that dodgy thermister now, and check the cabling.

Any tips on taking off the inlet manifold?

Nick; do you have that Bosch part No for the Thermister?

Best Regards
Darren

[Chris Williams]

Any tips on taking off the inlet manifold?

Probably only the common sence ones, use plenty of WD40 or ehatever a few days before, try tapping the bolts (4) on there heads using a long socket extention and a hammer, perhaps try to nip it up tighter a little bit first. I think its the top left one is the worst a 'wobble' bar extention works well on this one!

Chris

[NickT]

Darren C Wrote:Hi All,

Definately the thermister, put a 10Kohm resistor in pins 9 & 11 on idle ECU, and she purrs like a kitten,.

Thanks everyone for your help. Especially Nick T, for the resistor trick.

13p at Maplins!

Just need to change that dodgy thermister now, and check the cabling.

Any tips on taking off the inlet manifold?

Nick; do you have that Bosch part No for the Thermister?

Best Regards
Darren

BOSCH 0 280 130 028

Look in:

http://www.k-jet.org/files/greenbooks/T ... epairs.pdf

PDF page 7 (Specifications) & 8 (Resistance vs Temp Curve top graph)

NickT

[NickT]

Darren C Wrote:Hi All,

Definately the thermister, put a 10Kohm resistor in pins 9 & 11 on idle ECU, and she purrs like a kitten,.

Thanks everyone for your help. Especially Nick T, for the resistor trick.

13p at Maplins!

Just need to change that dodgy thermister now, and check the cabling.

Any tips on taking off the inlet manifold?

Nick; do you have that Bosch part No for the Thermister?

Best Regards
Darren

BOSCH 0 280 130 028

Look in:

http://www.k-jet.org/files/greenbooks/T ... epairs.pdf

PDF page 7 (Specifications) & 8 (Resistance vs Temp Curve top graph)

I would check the wiring from the ECU back, as a broken wire and/ or multi plug connection at fault is easier to fix than remove the inlet manifold.

If you do have to remove the inlet manifold, call me and i will give you the procedure on correctly setting up the throttle plate etc.

Good luck.

NickT

NickT

[steve.s]

while you're in clean fully and ht paint the valley of death.

also may be time to check the clutch is ok? easy to bleed when the manifold is off.

worth the few pounds to change plugs etc also.

[Darren C]

Hi Guy's,

Got the new Bosch Thermister this morning and went into the Valley of Death tonight after work.

Once I was in there I discovered that the Thermister was reading 12K ohms at 10 Deg C, the cable however was open circuit back to the ECU,

Having checked the plug etc all seemed well, eventually traced the cable back to the multiplug area by the coil. Found a poor contact on the Yellow/black cable in the bulkhead plug :lol:

Bent the female terminals back to a smaller diameter hole on all the pins in the plug, a squirt of WD40 and plugged it back in. Problem solved

While I'm in the valley I'll give it a spruce up so all is not wasted. Also I've checked the dizzy cap and rotor, changed the plugs and chaecked all Vacuum hoses and other electrical conections that you just can't get at normally!

Just need to get some copper washers for the fuel line banjo's tomorrow and hopefully get it all back together.

Thanks for your help everyone, and my top tip is...

Test all electrical faults with the half split method on the bulkhead connectors by the coil first!!!!

Best Regards
D