Thread: Fast Idle when coming to a stop.....

Hi bigdog,
99% that the overun is a sticking bypass valve. Conventional advice is to give it a quick spray & brush with carbie cleaner. However, I've found that this fix works a lot more reliably. Here's the extract from my post couple of years ago (& a link to the full thread at the end)

6) Stepper motor - usual advice is to whip it out and give it a clean with carby spray. However I think this is possibly the better way(?)
a) unscrew it from the plenum and reconnect the multi pin. put it into a clear plastic bag with an elastic band around the cable
b) stuff a large rag into the hole in the plenum ie one that won't get sucked in. Or get wrapped around pulleys - take care.
c) Start the engine. Revs will soar to around 2000. If it doesn't start adjust the rag to limit airflow. The ECU will activate the stepper motor and the plunger will be driven out of the housing. It may take a couple of start stops but the plunger and spring should fall into the bag - a gentle wiggle to assist may help.
d) carefully clean the threads, plunger and key way and relube. Don't use anything heavy like copper grease or lithium. I used a bicycle silicone chain lube called "ICE" and it's worked spot on for ages.
e) screw the thread back into the worm - trick bit as you need to align the keyway - it's a feel thing. flip the ignition on and off a few time (no start) to confirm ok, then put it all back together.

This thread http://www.aulro.com/afvb/classic-ra...uctuation.html details the full idle set up procedure, but note as yours is a auto your base idle should be lower - 450>550rpm according to the workshop manual and, once under ecu control 600rpm in gear no air con.
(mine was a manual that tended to stall when the a/c was on (since fixed) hence I set base at 700>800)

Hopefully, going through the full idle setup will also solve the hesitation issues
cheers Chris

Hiya Hobbes,further to cleaning out the idle bypass valve(stepper motor)i was reading this the other day,and sounds like it may pertain to the problem you having re the high idle.scroll down to road speed sensor symptoms.
This entire thread has some great insight into the good old 14cux system,cheers westy
LAND ROVER

Hi westy (& big dog),
(note it was bigdog with the current prob - not me!)

Yup – seen this article before. However, whilst he's for correct in the operating characteristics of the vehicle speed sensor, the assumptions he makes that the idle threshold is too low and affect driveability negatively are possibly misleading in the context of anything other than a dedicated off-roader.

Once vehicle speed exceeds 8km/h the bypass air valve will maintain idle at around 1200rpm. This significantly helps vehicle refinement on closed throttle, slowing the rate of engine deceleration. This higher idle not only helps with gear changes but also allows for additional significant loads such as aircon compressor, and the fact that on a closed throttle deceleration fuel will be partially cut.
It’s also “buying some time “ for the BAV to get it’s act together once vehicle stops.
Once the vehicle slows below 8km/h the ecu, which also gets inputs from the aircon compressor and the gear position switch, will pulse the BAV to close/open via a hunt process to maintain idle at 750 ish.

On a dedicated off-roader this lack of engine braking may be a bit of a pita: On a lightweight sports like a TVR it’ll help stop the back wheels from locking when the throttle snaps shut! And on a RR makes life a bit less clunky…

Back to bigdogs issue (if you haven’t got it sorted) on the RR the VSS also provides the feed to the electronic speedo: if the speedo is working so is the VSS. If the VSS is still suspected it’s output can be checked with a multimeter at pin 7 of the ecu.

My money is still on a sticky BAV, but other culprits are possibly an air leak, throttle butterfly not closing completely, throttle position sensor faulty, dirty MAF.

One thing to note is that the 14cux has a non-volatile memory – it’s worth disconnecting battery for a couple of minutes to reset any fault codes as a start.