nice tools to have

 

Something interesting i discovered.
if my battery goes totally dead (not even enough power to unlock the car) or i leave it disconnected for a decent period of time when i start the car the idle drops back down to more like where it should be.
it drops to ~800 in park and ~700 in drive while still warming up.
but then if i shut down the car and start it again the idle will have climbed back high again.

which indicates to me it is something in the way the ecm has learnt to adjust to a bad tps.
Idle normal, then get a different voltage reading, adjust and bamn high idle.
interesting.
i will certainly make mention of this to the mechanic

 

There is a 5,0 volt reference generated by the ECU that deeds 1/2 of the engine sensors like the TPS but not the MAF as it gets straight B +

At some point in the battery draining and the voltage to the ECU it will not be able to supply the 5.0 reference voltage and the TPS will fail as the expected.range

The return signal to the ECU will start off being below the 0.60 volt value and rejected by the ECU

Does the ECU carry on forward with no TPS sensor value data or just shut down as a complete failure

Just mesaging your brain

 

makes me think...
I wonder what would happen if I disconnected the TPS?
would it continually idle with a decent value maybe?

 

At worst, it wouldn't run at all.

At best, it idles at closed loop, but you wouldn't be able to accelerate the car. There's nothing to tell the car that you are putting your foot on the gas....except for the MAF.

The throttle butterfly has a spine that seats into the TPS. When you put your foot on the gas, the pedal pulls on a cable, opening the throttle butterfly and actuating the TPS that it's connected to. That TPS then tell the ECU what's going on.

If you want to operate the car in closed loop, disconnect the Coolant Temp Sensor. Your car will run on a preprogrammed fuelling map. It will run inefficiently, but probably smoothly for it will be overfuelling the car (almost) all the time.

 

Ok so...
i just got her back from the mechanic today.
He fixed my front crank seal oil leak which is good.
he checked my water rail where it was leaking. It is currently not leaking, can be seen it was leaking with coolant down side of block but as it was currently not leaking he thought it best to leave it be for now.
adjusted my handbrake best he could, tho noted i need a new left handbrake shoe due to missing lining.
and told me that overall otherwise my cat is in good health.

but...
he was unable to fix the high idle.
he tried and tested essentially everything and has come back with the diagnosis of it seems apparent that it must need a new ECU due to a software issue.
it appears the IACV is opening to allow cold start, but not getting told to close.
this is his diagnosis report.

-Removed throttle cable springs and linkages
Adjust throttle blade to factor specs. It was closing slightly too far.
- Remove and wash throttle position sensor and set to factor specs. .6v @idle
- Removed Idle speed stepper motor and checked for binding, OK
- Check idle motor resistance, OK.
- Manually adjusted stepper motor and can get low idle however when plugged back in it re opens and causes high idle again
- Remove ECU and chec continuity and voltage of Idle speed motor wiring, OK.
- Fit working "test" idle motor off another X300 car, same problem (motor came from his own XJR. so definitely known working)
- Refit original idle motor and all throttle linkages.
- Check ECU for fault codes, None

only thing he can think is the ECU is not telling it to close.
goes along with the fact if i remove the coolant temp sensor the idle climbs up really high but when plugged back in it does not drop and requires the care to be turned off and on again to reduce the idle.

 

What happens with yours is the TPS idle voltage value is above what's stored as idle voltage value in the ECU. Plug in OBD scanner and check what it is with the foot off the pedal, any scanner will do, it will either show it in V or %(which you can then convert to volts). Because your idle TPS voltage value is above what's stored in ECU, ECU thinks you have slightly pressed pedal and moves the IACV to its rest position, slightly up, allowing extra air(even with the throttle up), extra fuel and that's why you have high idle.

Because you specifically mentioned:
'Adjust throttle blade to factor specs. It was closing slightly too far.'

This basically means that if throttle blade was closing too far and the factory gap which should be 0.002" was even lower than that, you've effectively increased the idle TPS value which put you even further away from normal idle.

I'll give you some instructions how to get this back to normal, go through them and report back, it is possible to get round this without doing a TPS adaptation.

1. Plug in your OBD scanner and check TPS voltage with the foot off the pedal, it should either be in V or %, record it. It should be around 11.50% or 0.67V. Let us know what it is.
2. Turn the adjustment screw on the throttle body OUT as far as you can.
3. Turn the throttle closed with your hand, just to make sure its not sticking on a weak spring or cable. For that you can even temporarily loosen the throttle cable so we know for sure that's not pulling the throttle blade
4. Switch the car on and check the TPS voltage in OBD again and let us know what it is. If the idle is fine record the TPS voltage - this is exactly what is stored in ECU as idle TPS voltage and whatever you do later with the whole setup it cant go any higher than 0.02V of that value!
5. If the idle is still high, check the OBD TPS voltage, let us know what it is. You still need to lower it down. To do this, you will need to get the car on a ramp, loosen the TPS screws and turn it, there should be a mm of play, enough to lower or increase the OBD TPS voltage by 0.1V. Hopefully that gets you in a spot where idle settles down and you should know what value it must be to have normal idle.

Let us know how you get on with this and we can go from there.

 

After changing the ABS actuator and the throttle body, I struggled with this for weeks. Drove me to drink. After going through all the steps to resolve it, I called the Jag dealership and asked them if they could reset my TPS. After telling them the year, they said their Windows diagnostic computer was unreliable and did not want to help. I called around to other dealers within 200 miles and was pretty much told the same thing. Then one of the members on this board said they would send one to me. I hooked it up, and reset the TPS, and the problem was resolved in the 10 minutes that I had it hooked up. I feel much better now, and AA is working out well.

 

CDMA ,.

Was that you that needed a X300 radiator fan as I obtained 2 with one for me ?

 

Was not me. I have a few extra from the parts cars that I had. Thanks for asking

 

the mechanic is a specialist who knows these well and drives one himself. Has been doing jags for years so i trust what he says.
i do feel the factory reset with a wds may solve the issue tho.

he fixed the throttle stop before fixing the tps voltage.
before my torque app told me throttle was 12.5%.
now it tells me it is 10.89% so it is good. Throttle open.
the tps has been reset to idle voltage of 0.6v
So when the throttle blade is fully closed, the tps is showing .6v so it is exactly correct as it should be
i had also been through this all
myself before too. I did have my diagnoatics written in another thread somewhere.

yes i can play around with and check voltages but that was just done.
but no.
there is not an adjustment via the screws on the x300.
unless you modify the tps.
which i do not wish to do.

everything you mention the mechanic just did.
the voltages are reading correct.
The iacv is just not closing.
it is opening on start, can be manually closed and get a good idle, but when plugged back in it will open.

 

My best guess is that the tps maybe was incorrect and the ecu had adjusted.
and now the tps is good but the ecu is expecting something different.

my thought is tho, if it is learnt ecu behavior would disconnecting the battery for a while not reset it to factory?
i know on some cars you use a jumper pin across 2 wires on the obdii port to reset the ecu.
not something i would wanna try but something that makes me think

 

You're mixing something up. You said your TPS voltage was initially at 12.5% (0.625V), then you said your mechanic adjusted stop gap as it was closing too far which means he screwed the stop gap IN and then suddenly your TPS reports 10.89%(0.5445V) which makes no sense whatsoever as screwing the stop gap screw IN increases TPS reading, not lowers it. You can get ~0.08V adjustment in the TPS via the screws, I know it looks like there's no adjustment in it but you can see yourself by loosening the screws turning it slightly and observing obd reading at the same time. That's usually plenty enough to lower or increase idle TPS voltage and RPMs in the process, hence why its so important to get that happy TPS reading from OBD before disturbing TB and TPS in any way or when replacing TPS as its quite easy to mess it up by over 0.02V which is enough to mess your idle.
I would still attempt to lower that value down and hopefully that lets you at least find the value where ECU is happy, if not then your option is another ECU or TPS adaptation which I guess might be tricky in the land down under.
If you find a breaker and don't want to be bothered with this, simply get a matching ECU and throttle body with TPS still attached to it.

 

No no.
not messing anything up.
he adjusted the throttle stop.
then he adjusted the tps after that.
(also i do expect some inaccuracy from the torque app and elm327)

there is one bloke i think around here who can do the adaption

 

So @katar83 what are your thoughts on this.

after battery was disconnected for a while, car was started and the idle was good.
then the car was turned off and restarted and idle went high again.
this happened a few times.

now i will check this again on the weekend now after its mechanic visit and see what happens.

 

This is so confusing, you're definitely mixing something up or not telling the full story
What do you mean by 'he adjusted the TPS after that', in your previous post you said there's no adjustment for the TPS(I know there is but that's a different step).
Screwing in or out the throttle stop screw is what sets the lowest TPS voltage but it also changes the throttle gap. You can further add to it by turning the TPS with its screws loosened. If you're worried about OBD scanner being somehow inaccurate, simply use a digital multimeter, directly, on the signal wire.

That said, if you think you can do a TPS adaptation, no point in looking into it further, just go for it
Your car battery disconnecting and reconnecting probably just messes up IACV initially, there is nothing except for TPS adaptation that can reset the value in ECU.

 

i am not messing anything up and i am certainly telling the full story.
there is no adjustment in the screws to my knowledge.
if there is adjustment in the screws so be it.
but every single post i have seen on the topic says there is not and holes must be drilled.
except for what you say. Not saying you are wring. I wouldn’t say that as I don’t know. But someone is wrong. Either those that say there is not. Or you who says there is.
so i can only go off the information given to me.
now i don’t know exactly what the mechanic did, but as he said and noted he removed the tps, cleaned and adjusted it so it read .6v at idle.
But yes as you say and as i said before i need it hooked up to a wds and reprogrammed.

 

This is a copy of something i posted a while back in a previous thread showing the reading i had when previously testing my tps

“ok. so i tested again and got proper reading,
it seems that it is reading too low of voltage.
throttle closed it is reading .53v
it then moves and climbs nicely reaching full 5.01v at WOT.
so for the most part it is noce. but it is reading the throttle as more closed than it should be and obviously opening the iacv too much”

 

Well, so he messed it up as what he listed and in what order doesn't make any sense whatsoever
If he simply adjusted throttle gap to 0.002" as he should have and then adjusted TPS by adjusting the throttle stop screw until it showed 0.6V, he simply messed up the throttle gap again.
Also its contradicting what you're saying since you said your TPS is currently showing 10.89%(0.5445V) with the foot of the pedal.
The 0.6V is a red herring too by the way, this is just ideal value but rarely achieved in real world, that's why there was a factory TPS adaptation. I had cars were idle TPS voltage was 0.54V, 0.62V and 0.71V.
Like I said, go with the adaptation if you can, you'll save yourself a lot of trouble.

 

but he is saying they are 2 different adjustments.

as far as the throttle blade, i get it.
it was closing a little too far and therefore occasionally sticking. It was going beyond the 0.002 gap.
it is not doing that anymore

as far as the tps i am not sure exactly how he adjusted it but not from the throttle stop screw.

i will do a reading when i get a chance and see what it reads.
but yeah I don’t trust my tourque app to be 100% accurate for a few reasons. It seems to be a little laggy, and also when it is running for a little while, the sensor readouts freeze up and stop being updated.
like the rpm
and throttle will just stop at a particular reading.

I don’t know if this is an app problem or indicitive of a problem in the ecu.