Setting the Throttle Butterfly
Discussion
It should have a machined 'beveled' edge one way at the the top and the other way at the bottom. They can build up carbon on these edges so cleaning with brake cleaner is a good idea..Although don't use to much and then start it.!. The butterfly should be shut tight by the throttle spring.
I set mine perfectly closed using the grub screw adjuster . Note, this maybe very tight so avoid 'rounding' it off.
My throttle body was on the bench, so I used the depth probe of a vernier caliper to measure the distance from the edge of air intake opening to the throttle flap. Take two measurements,180 degree apart and 90 degree from the rotation axis. when they are exactly the same, I assumed the flap was totally closed.
Seemed to work successfully for me
My throttle body was on the bench, so I used the depth probe of a vernier caliper to measure the distance from the edge of air intake opening to the throttle flap. Take two measurements,180 degree apart and 90 degree from the rotation axis. when they are exactly the same, I assumed the flap was totally closed.
Seemed to work successfully for me
However you do need a slight air-gap otherwise the butterfly will keep wedging itself in the bore making for very jerky on-off throttle action , if you apply very gentle closing action to the butterfly to replicate the three closing return springs and it sticks you need to crack it open more
Unless you have a real reason to make this adjustment I would leave well alone. It is a factory setting which should never need changing.
If it is out of adjustment then the most likely reason is the shaft/bearing is worn in which case adjustment is not going to solve the problem.
Steve
If it is out of adjustment then the most likely reason is the shaft/bearing is worn in which case adjustment is not going to solve the problem.
Steve
Steve_D said:
Unless you have a real reason to make this adjustment I would leave well alone. It is a factory setting which should never need changing.
If it is out of adjustment then the most likely reason is the shaft/bearing is worn in which case adjustment is not going to solve the problem.
Steve
Good point Steve If it is out of adjustment then the most likely reason is the shaft/bearing is worn in which case adjustment is not going to solve the problem.
Steve
just sometimes owners do tinker with these things however to cure another issue and dont put things back how they found them 
no wonder LR stuck that set screw in a hard to reach location 
I moved the throttle stop grub screw from underneath the throttle body to the top, but after much experimentation ended up with the butterfly in the closed position and the base idle set via..... errrr, the base idle screw 
On my Canems system I run an unnaturally high base idle of 1,250rpm then use scatter spark to bring it down to my preferred 1,000rpm idle, the protocol is set so scatter spark closed loop idle management is only effective below 1,300rpm, and only if the TPS is below 2% too, both rules must be met or scatter spark is effectively disabled.
With the correct decay value this strategy works brilliantly, the effect is to smooth gear changes as the 1,250rpm base idle is still held for the split second you come off the throttle, dip the clutch and swap cogs, the extra engine speed basically bridges gear shifts perfectly delivering far smoother progress as you row the gears through slower driving speed urban areas.
As you approach a junction and are slowing to a stop you're typically braking with your foot completely off the accelerator pedal, as the revs drop below 1,350rpm the ECU reads this and the zero TPS position and starts to pull ignition timing, the rate it does this is called the decay, get the decay right and you'll still enjoy the gear bridging effect, but before you've even stopped rolling up to a junction the engine will already be sat at a lovely stable 1,000rpm idle.
This raised base idle scatter spark strategy also acts to stop any unwanted excessively low dips in engine speed on snap throttle lift offs say when you're approaching a junction a bit fast and braking harder than normal, or in the event of an emergency stop, I have a 1,300rpm fast idle target that serves to help here too. Ordinarily in both these rapid stop scenarios it's common to see engine speed dip excessively to the point where you're close to a stall, with the raised base idle scatter spark strategy the effect is the engine speed simply can't and won't dip lower than an absolute low of 950rpm.
I've also found its best to really just leave the Bosch idle valve to take care of the extra air requirements during warm up, if you do run it in full closed loop mode configure it so it's only active below 950rpm, like this and with very lazy responding response time settings its just there to save a stall if the driver makes a mistake and is a bit clumsy with the clutch pedal as he pulls away from a junction (we've all done it).
For closed loop idle management on a fully warmed engine there's absolutely no question scatter spark is way way better than trying to manage idle with a Bosch idle valve. You do need to get your scatter spark settings, base idle ignition timing, and base idle screw position just right, but get it all working together in harmony and the car will drive massively smoother through town, have an insanely smooth idle and clumsy driver forgiving ant-stall characteristics.
I know you can't do all this with the 14CUX but what you may not realise is your good old Lucas ECU actually tries to achieve something similar, but using just air as it can't control ignition timing. The 14CUX uses the stepper motor and road speed signal, the trouble is while this worked well from new in a Range Rover, TVR's road speed signal box is a bit craaapy and your 22 year old Lucas stepper motor will have had a very hard life getting cooked in the roasting TVR engine bay.
I hope however those running an after market ECU will find my raised base idle scatter spark strategy helpful, I found it transformed the drivability of my TVR which now competes on user-friendliness with any modern car, all of which have massively more sophisticated engine management systems than the typical after market ECUs used on our cars.
On my Canems system I run an unnaturally high base idle of 1,250rpm then use scatter spark to bring it down to my preferred 1,000rpm idle, the protocol is set so scatter spark closed loop idle management is only effective below 1,300rpm, and only if the TPS is below 2% too, both rules must be met or scatter spark is effectively disabled.
With the correct decay value this strategy works brilliantly, the effect is to smooth gear changes as the 1,250rpm base idle is still held for the split second you come off the throttle, dip the clutch and swap cogs, the extra engine speed basically bridges gear shifts perfectly delivering far smoother progress as you row the gears through slower driving speed urban areas.
As you approach a junction and are slowing to a stop you're typically braking with your foot completely off the accelerator pedal, as the revs drop below 1,350rpm the ECU reads this and the zero TPS position and starts to pull ignition timing, the rate it does this is called the decay, get the decay right and you'll still enjoy the gear bridging effect, but before you've even stopped rolling up to a junction the engine will already be sat at a lovely stable 1,000rpm idle.
This raised base idle scatter spark strategy also acts to stop any unwanted excessively low dips in engine speed on snap throttle lift offs say when you're approaching a junction a bit fast and braking harder than normal, or in the event of an emergency stop, I have a 1,300rpm fast idle target that serves to help here too. Ordinarily in both these rapid stop scenarios it's common to see engine speed dip excessively to the point where you're close to a stall, with the raised base idle scatter spark strategy the effect is the engine speed simply can't and won't dip lower than an absolute low of 950rpm.
I've also found its best to really just leave the Bosch idle valve to take care of the extra air requirements during warm up, if you do run it in full closed loop mode configure it so it's only active below 950rpm, like this and with very lazy responding response time settings its just there to save a stall if the driver makes a mistake and is a bit clumsy with the clutch pedal as he pulls away from a junction (we've all done it
). For closed loop idle management on a fully warmed engine there's absolutely no question scatter spark is way way better than trying to manage idle with a Bosch idle valve. You do need to get your scatter spark settings, base idle ignition timing, and base idle screw position just right, but get it all working together in harmony and the car will drive massively smoother through town, have an insanely smooth idle and clumsy driver forgiving ant-stall characteristics.
I know you can't do all this with the 14CUX but what you may not realise is your good old Lucas ECU actually tries to achieve something similar, but using just air as it can't control ignition timing. The 14CUX uses the stepper motor and road speed signal, the trouble is while this worked well from new in a Range Rover, TVR's road speed signal box is a bit craaapy and your 22 year old Lucas stepper motor will have had a very hard life getting cooked in the roasting TVR engine bay.
I hope however those running an after market ECU will find my raised base idle scatter spark strategy helpful, I found it transformed the drivability of my TVR which now competes on user-friendliness with any modern car, all of which have massively more sophisticated engine management systems than the typical after market ECUs used on our cars.
no more than you want the idle air bypass gallery or screw or ICV dirty for that matter That was referring to the cerb 4.2 as an aid to balancing airflows on adjacent butterflies .. ie only clean the low flowing butterflies and leave the high flowing ones alone. Not applicable to the RV8 stuff.
One of my pet hates is service centres not cleaning the throttle area on the rv8
One of my pet hates is service centres not cleaning the throttle area on the rv8
Steve_D said:
Unless you have a real reason to make this adjustment I would leave well alone. It is a factory setting which should never need changing.
If it is out of adjustment then the most likely reason is the shaft/bearing is worn in which case adjustment is not going to solve the problem.
Steve
Good stuff......If it is out of adjustment then the most likely reason is the shaft/bearing is worn in which case adjustment is not going to solve the problem.
Steve
In my case I have tried to set the base idle but even clamping off the bypass and shutting the idle screw fully shut I cant get revs below 850rpm. I have removed all inlet parts cleaned and resealed them (with a smear of blue hylomar). I cant find any induction leaks after blocking off all connections and spraying easy start around plenum area.
In conclusion I suspect either
1. Butterfly is not fully closing
2. Butterfly bearing is worn allowing air past ( but less likely as easy start spray in that area has no effect on rpm)
Hence my desire to check and adjust butterfly if required.
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