Hi all,

I'm in the process of resetting my base idle and for those wishing to know the the correct procedure I'll document it at the end of this post. Whilst I have had some success I suspect my stepper motor (IACV) is faulty so I've got a new one on order.

My concern also relates to the IACV wiring harness. When disconnected and looking at the end profile of the harness, the haynes manual (page 4:12 - diagram 13.23a) suggests that the voltage of each wire (pin) should be as follows keeping in mind that all wires have a base colour of orange;

(harness clip -top of photo)

0.4v - 11.2v

11.2v - 0.4v

however on my Jag I have the following;

(harness clip)
Yellow - Black
0.4v - 11.2v

Green - Red
0.4v - 11.2v
[/IMG]
corresponding wire colour codes - white arrow represents the orange/black wire

Before I go ripping out my dash looking at the ECU I'm wondering if anyone out there with an '88 could please check their Jag, both wire colours and voltages, to either confirm or reject my assumption that I think that the Haynes Manual may be incorrect regarding the voltages?

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In regards to the correct procedure for setting the base idle here it is for future reference which comes courtesy of AJ6 FAULT CODES AND IDLE SETTING / AJ6 Engineering

I suggest those that who are not familiar with it's location locate the air bypass adjustment screw which is very near to the stepper motor (IACV) within the same housing. It's adjusted using the appropriate size allen key. It's also very often loose so first thing to do is unscrew it and wrap some teflon tape around the thread to help keep it in position

[/IMG]

IDLE STEPPER MOTOR SETTING PROCEDURE 3.6 Litre


You will need a 5w 100ohm resistor for this process which is available from any electronics store.



-set TPS to 0.32 volts at closed throttle
-set throttle butterfly to 0.05mm or 0.002"

1. Run engine until fully warm.
2. Switch off and remove connector from coolant sensor.
3. Insert 100 ohm resistor across coolant connector terminals.
4. Switch on ignition and after 10 seconds remove connector from stepper motor (which will now be fully seated and closing off idle orifice).
5. Switch off ignition, remove 100 ohm resistor and reconnect coolant sensor.
6. Start engine and set base idle speed to 600 r.p.m. via air bypass adjustment screw near to stepper motor.
7. Reconnect stepper motor - idle should now stabilize around 700 r.p.m.
8. Your done - enjoy your smoother performing engine!

For those with a proper way of diagnosing emissions:

1. Check idle CO2 - factory setting quoted as 1-2% but we find that most engines idle best with a weak setting around 1% or even slightly less depending on HC emission being stable. This is can be done via the set screw hidden away on top of the MAF

3.2 & 4.0 Litre


-set TPS to 0.6 volts at closed throttle
-set throttle butterfly to 0.05mm or 0.002"

1. Run engine until fully warm.
2. Switch off ignition.
3. After 5 seconds switch on ignition - wait 5 seconds - remove connector from stepper motor.
4. Switch off ignition.
5. Wait 15 seconds then replace connector on stepper motor.
6. Repeat operation sequence 3 - 5 twice - on the last occasion do not reconnect stepper motor.
7. Start engine and set base idle to 550 - 600 r.p.m. via air bypass adjuster.
8. Switch ignition off and reconnect idle stepper motor.
9. Restart engine - idle speed should now stabilise around speed shown below.
10. Your done - enjoy your smoother performing engine!
11. Check idle CO as for 3.6 (if non-cat).

Specified Idle Speeds

Cold in neutral - 800 (Auto)
Hot in neutral - 700 (Auto)
Cold in drive - 650 (Auto)
Hot in drive - 580 (Auto) (3.2L = 650)
Hot in Neutral - 800 (Manual)


Note: Cold idle speeds will be slightly higher at very low temperatures.
If the above procedures do not result in stable idling check that the throttle potentiometer is correctly set. Whilst the ECU will automatically compensate for minor errors within the range of the adaptive memory, a badly adjusted throttle potentiometer can cause spurious drive-ability and idling problems.



- don't forget to reset your trip computer to check future fuel
consumption figures