I’ve been tinkering with the Lotus over the last few days and with the kind assistance of Klaus now have nicely balanced throttle bodies having replaced the adjustable balance screw for a longer one and tensioned with a spring. Disconnected the IACV, adjusted the idle then the new balancing screw and now way closer to where it should be. This took some work to see how the adjusting screw brings the two throttle bodies into balance but now very happy with the result.
However with engine diagnostics plugged into the OBD I tried a throttle reset and noticed the throttle pedal at full travel is only measuring 92.94% not 100%.
So simple question and I’m hoping there is a simple answer though being a Lotus perhaps that is being ambitious! How does one adjust the throttle cable and / mechanism to realise 100% travel ? I assume this is a mechanical adjustment required as the TPS is not ‘seeing’ full travel, i.e. 100%.
A quick look on the Search function hasn’t found what I was looking for as yet.
As no one else is answering I give it a try:
If I remember right you can turn the TPS a little within its fixing screws. You may drill slightly bigger holes into the plactic housing of the TPS if there is not enough movement available.
On the other hand the most important thing is that the butterflies are fully open on full throttle and not that the TPS reads 100%. The EFI ECU calculates the engine load from the MAP readings. The throttle position sensor is mainly used to detect sudden changes when accelerating. So I’m not sure if the full throttle reading of 93% at full throttle is really a problem.
I’m not 100% sure about all that and someone with better knowledge may correct me.
Thanks for that guys. I will look into it a little further. That said I do wonder if it is a limitation of the OBD reader that I have which isn’t detecting a small throttle movement from idle. I say this as I pressed the accelerator really gently to pick up the the revs by 300/400rpm (which is recognised on the OBD reader) but still showed 0% throttle…
Craig - the balance adjustment screw replacement was as described by Klaus in his thread “improving VHPD driveability”. Reason being the original may not provide enough range of adjustment (it is a very short allen headed bolt). Cylinders 1&2 were distinctly quieter that 3 &4, now they are very close the car feels like it has bigger lungs, low and mid range pull is notable.
I don’t think that this is an OBD reader limitation but that the travel of your TPS is not in sync witht the throlle shaft movement. Unscrew the TPS fixing bolts and then turn the TPS against the throttle opening sense while the OBD reader is connected showing the throttle position read out. When the throttle read out just starts to rise you found the position where the TPS should be fixed.
In our private message exchange about the balancing topic I wrote you about turning the idle adjustment screw in as much as possible. Yours was nearly closed and that may be the cause for the non existing TPS readout on the first bit of throttle shaft movement. So best would be to first adjust the idle screw by turning it in as much as possible before the idle rpm inceases (the IACV needs to be connected). If that is done you set the position of the TPS as described above.
The VHPD drivability is very sensible to all sort of faults. To eliminate sensor failure I would suggest to just buy a new TPS before setting all the things up. They do wear out as there are electro-mechanical items. There are cheap ones on Ebay UK, have a look here: https://www.ebay.co.uk/itm/162364189261
Klaus - excellent advice as always. That does make sense that the TPS is not in sync with the throttle shaft movement.
My TPS was replaced last year but no harm ordering another to be sure. I hadn’t appreciated the reset process and of course doing this with OBD reader connected will help ensure the correct position for reset,
Craig - I followed the advice from DVA of listening to the volume from each cylinder. Once you ‘tune in’ your ear it is very clear where there is a variation from one trumpet to another. So it won’t be exact but the set up is now way more in balance than previously. I don’t have numbers for each cylinder without a synchrometer but I am confident they are really quite close. I have also marked up the balance screw head and spring to act as a reference point for that ‘balance point’. I plan to pull the plugs after engine is up to temperature and see how they look.
The throttle bodies had been balanced by a garage not long ago using a synchrometer so one can only guess how well they did that job.
Looking forward to the next test drive once this rain passes!
By way of update for any interested party (may be of use for future reference).
New TPS installed. TPS reset procedure followed to calibrate to ECU (seems the ECU is a little slow to respond to new sensor installed and resetting throttle range). A couple of attempts and values appeared normal.
Plugs pulled following throttle body rebalancing procedure. All a nice carrot colour, no blackening or soot and all consistent colouring.
Process was carried out with fuel relay disabled, all plugs removed and full throttle. Numbers certainly appear consistent, no idea where they should be or what is a typical range?
Idle inlet manifold pressure readings around 62-64kPa.
Short term fuel trim around -7 to -14% so still rich on idle.
I feel the car is really getting there now (test drive proved very positive pull throughout rev range) though so still something to chase with slight rich running at idle though maybe this is somewhat attributable to the 190bhp ECU and no CAT?
Did you manage to get 100% travel in the end Rich?
After trying to balnce my TBs and cleaning my IACV, I’ve got throttle problems now. My TPS is reading 13 - 92%, which is making it idle way too high. New TPS is on order but the thing is, the throttle pretty much returns to the same position everytime, but I can physically force at the engine end to get it down to around 5% - is that normal? TPS reset was unsucessful, but then the 5 pu=edal pump thing is for MEMs instead of EFi cars? I’ve also noticed that the butterflys seem to be cracked open slightly at ‘idle’ is that right??
Nothing is jamming at the pedal, idle screw is backed right off and blocking the IACV makes no difference; butterflies jamming or a weak spring on the TB?
Probably best the more knowledgeable folks give you technical direction on what to do but from my experience after balancing the throttle bodies the butterflies appeared closed, barely a perceptible gap visible to my eye.
I would have to reread the info I was given on throttle body balancing but if I recall correctly the IACV should ideally be disconnected whilst carrying out this procedure.
Regarding the TPS reset procedure I think that has been shown to work for the Esprit V8 hence EFI engine management cars including the Exige.
As for gaining the the full throttle range again yes I think that was all back again but would need the engine diagnostic plugging in again to check. Might do that when I tax the car again which could be soon!
On my car I noticed that, when assembled to the head, the two throttle bodies tend to seize one against
the other in the closed position, causing the non complete throttle closure.
In order to get rid of the problem we lowered one part of the linkage and after this the throttle closed freely.
Thanks for the feedback guys, much appreciated. Looking again, the butterlies seem relatively smooth and the throttle snaps back to roughly the same place, the only thing I’m unsure of is why it doesn’t flyback against a ‘stop’, as you can see here at the end of the video that I can close the throttle slightly further at the TB:
This was exactly my problem.
Taking the two throttle bodies apart they both snapped back without any problem, but
reinstalled on the head due to a little distortion in the alignment this caused the problem
you are describing.
I wouldn’t have thought so Craig. I will try and check tomorrow. Does that also have the effect of pushing the butterflies a little more closed?
I did notice on mine the throttle cable bracket was slightly bent - it’s not very strong metal. Maybe just the camera moving in your video but looks like the bracket has some flex / movement as you push home the throttle actuator? Might worth checking that too to make sure it isn’t just the bracket limiting the correct movement of the throttle cable.
I noticed the same thing as Evoman: it looks like the bracket of the throttle cables is moving towards the throttle bodies when you are using the screwdriver to forcefully close it. Is the throttle cable really slack? I would repeat the procedure with a fully disconnected throttle cable and see if things change.
Thanks - I’ve done some more investigating, and wound down the balance screw and lo and behold it closes a tiny bit more. So I guess although it looks like the butterflies weren’t fullly closed, one of them was starting to bind, preventing the rest from closing.
So now the throttle readings are more consistent; I had nice and steady readings from 10% - 98%. TPS by Colgy, on Flickr
The creaking is the cable, not my old knees…
Tried to calibrate it and it didn’t seem to work, however after a couple of hours it has now changed from 3.5% - 92%. I appear to be getting full throttle at the TBs and the throttle cable is slack at the pedal (~10mm of pedal movement before the cable is tensioned) - not sure why it isn’t calibrating correctly though!
Have you adjusted the position of the TPS itself? That could be it if you haven’t looked at this yet. When you install a new one it seemingly takes a few attempts for the ECU to recognise the new TPS.
I had similar pain of spending hours trying to figure out why the throttle range wasn’t being recognised by the ECU with the OBD reading. Having apparently ruled out all mechanical aspects involving the throttle cable and linkage itself I did end up fitting a new Elise Parts upgraded throttle linkage and fitted a new TPS shortly after followed by the gear linkage upgrade too though that clearly has nothing to do with the throttle travel issue!
I haven’t adjusted the TPS yet, as not convinced that’s required. Full throttle is now 95%, so the ECU is definitely doing some sort of calibration - still investigating this!
I know realise what really buggered me up was that I had the throttle pedal depressed about 20% to make access to the screws easier. At some point, I must have cycled the ignition and the car ‘learned’ the new position resulting in the car idling at 5000 rpm! I then backed right off the idle and balance screws, which then gave me further issues
I also found that the pedal stop wasn’t wound out far enough, so the cable was being stretched tight. This in turn was bending/flexing the bracket, so thanks for the observation - all fixed now and I still have full travel on the TB when operating the loud pedal.
With the TPS reading at 0% now, had a go at balancing the TBs. Started off by increasing the idle speed until just before speed actually started to rise (IACV fully closed) and worked from there; without doing this the readings were even further apart. Took me a while to realise that the idle screw opens all cylinders (but doesn’t necessarily increase idle speed!), whereas balance screw just does 3&4. Looking at the previous results, the TBs were closed further at idle:
…1…2… 3…4
Initial…3.75… 2.75…1.5…2.25
Final…4.6…3.6…3.8…4.6
Cylinders 3&4 are the ones which are adjusted using the balance screw. You can see that the screw was too short, which meant that they weren’t as open as cylinders 1&2. Cylinder 3 also appears to have been the one that was binding slightly, because it was further shut and prevented the other cylinders & throttle shaft from fully shutting. Doesn’t appear to be an easy way to balance individual cylinders without modifying the TBs and I’m not sure how much difference it would make anyway. I tried a 0.5mm spring, but wasn’t convinced that it would be good enough to stop the balance screw from rotating, so ended up swapping it out for a nut and spring washer. Getting there now!
Just thought I would share some experiences here, for future reference when searching.
Calibration of the TPS seems possible by turning on the ignition, depressing the pedal a few times, and then leaving the igntiton off for a period. Each time this is done, it reduces the ‘% at idle’ by approximately 3%. Therefore, if you fit a new TPS and it shows 15% with the accelerator depressed, you need to repeat the calibration about 5 times.
I enlarged the mounting holes from 4mm to 5mm to allow the TPS to be twisted CCW and reader higher than normal. This had the effect of shifting the range up, which is exactly what was observed; now the 100% was achieved with anywhere from 90-100% pedal travel (OBD reading never went above 100%), but the TPS input was 15% without the pedal depressed. When the calibration at no throttle was peformed, the range (or ‘span’ in control speak) remained constant, which meant ending up back where I started at around 95% TPS input with the TBs fully open. Also tried a new TPS for EliseParts which had a slightly different resistance range (and weirdly wasn’t sprung - although no issue with fluctuations at idle), but made no difference after recalibration.
I’m not sure how much difference the <100% TPS will make, if the TPS is used just to tell the ECU of fast throttle change, as Klaus mentioned earlier. As I’m out of ideas on how to set the TPS range, I’m parking the problem for now!
I appear to be getting full throttle at the TBs and the throttle cable is slack at the pedal (~10mm of pedal movement before the cable is tensioned) - not sure why it isn’t calibrating correctly though! 
