Hi to all and the this is the first puzzle I have with my recently acquired 5 speed manual 96 XJR

Starts up and ticks over okish.....actually a bit revvy around 1200

Put in gear and pull away in first....then change to second....but in between gears in neutral the engine revs at the speed it was running at the point of change...say 2500...it might climb a bit to near 3000...then into second and all normal.....then change to third.....same thing happens.....etc etc....changing down is the same scenario.....it holds revs in neutral between shifts....but then if you coast to stationary the revs drop to 1200 again....

It actually feels like its holding the revs until you come to a stop and then the revs drop to normal almost as if it were speed related

This car is a 5 speed manual conversion done several years ago.....the ECU was not modded by Andy but the auto ECU was tricked?....this fault is new having behaved like a normal stick car up to recently when it has acquired this habit

However it does seem to me that an auto ECU might want to hold revs between auto shifts pretty much like what I'm seeing now with manual gear changes

Help

On another note....what's it like to drive a 5 speed manual X300 XJR.....nice.....why more people didn't choose this option when new I just don't know ...its not as crude as a lot of critics make out and makes the car more fun

 

Sounds like mine, and my mechanic thinks it could be a sticky throttle body that takes time for the return spring to close it back to idle when you're in neutral. Once the weather warms up here I'm planning on taking off the intake piping and tackling it with some throttle body cleaner, which hopefully will solve it.

 

I'm guessing here as this feature is a 'manual only' feature on S types. As an aid to smoother gear changing the ECU holds the revs up between changes, this helps as a 'synchromesh enhancer'....it won't do this in neutral as the ECU detects the vehicle is moving by the speed sensor input.

...as I say this is for S types with manual box....could simply be a sticky throttle plate and there was a mod' for stronger springs for the throttle plate (valve)

 

This is the weirdest.......

as I previously said....when changing gear the revs stay up in between gears.....2000 to 2500...then when i take it out of gear and coast to a halt in neutral the revs drop when the car is finally stationary.....

So.... I parked up on a long sloping road with the car ticking over in neutral....arguably high idle at about 1000 to 1200.....Then I let the car roll ahead while idling in neutral.......

I rolled to about 8mph......and the revs went up to 2000 / 2500 !! ....but my foot was off throttle ??....

Then I braked in neutral to stationary again and the revs dropped to tickover.... What the hell is is increasing the revs when I don't touch the accelerator.....its Like there is some speed related signal

I can only guess an auto ecu might send a signal like that...I have never experienced a manual trans car ever behaving like that...

when in neutral with your foot off the throttle it should not matter how fast the car is going....10mph or 100mph....the engine should simply idle....

Thoughts please

 

There is your answer, speed related synchro enhancer...nice feature

 

Forgot to add....this feature is also an aid to emissions regulation.
Most late cars will have this feature, look for a clutch pedal switch...even diesels!

 

The next time I'm back in UK with car I will video clip the problem.....on my car it seems to crude an over rev in neutral to be built in.....I have never known a manual cars revs to pick up rolling down a hill from idle when its in neutral and no clutch or throttle is applied so I don't think its a pedal switch...

Examples....

I come to a halt in second gear with revs in gear around 1200 just before you dip the clutch and go to neutral at full halt...as you would at a set of traffic lights....then stopped in neutral the revs immediately climb to 2500-3000 for about three to four seconds before finally dropping to idle

If coasting in neutral at any speed the revs will stay at 2500-3000 until I either put it into a gear or coast to a halt at which point the revs drop as previously described.

In one way imhoping its just a throttle body clean up or vaccum lines being needed to fix it but I'm equally curious to know what system in the car can cause revs to increase simply due to movement being detected resulting in neutral revs going up....

 

$64K Question: does the problem does exist if you rev' the car in neutral with the vehicle at rest?

If the answer is no, then it's most likely not the throttle body plate or idle speed control solenoid.....even a sticky throttle plate when felt by hand with the engine off, won't be as bad when the engine is turning on the overun due to the vacuum effect of the closed throttle plate.

Sorry I didn't make that clear what I meant about a clutch pedal switch. Old cars may not have a clutch pedal switch, if it's not got cruise control fitted for instance. Jag's 1990's engine management answer may have been a quick 'n dirty answer in that the ECU simply refers to the vehicle speed input, if it's moving ECU thinks "hang the revs between shifts"....crude but effective. The ECU's are different between manual and auto's...but then they shiuld be as the auto has a vehicle speed feedback feature of its own.

Clutch pedal switches are a common sight on modern cars without cruise as they use both speed input and a clutch pedal switch to tell the ECU the car is in-between gears, which is a more elegant solution, and you won't have the revs rising in neutral when 'coasting' in neutral if 'properly' programmed.

But, I'm still summerising here as I don't know for sure that this 'rev hanging' feature was fitted on old X300's and they maybe some other reason that is beyond me. I do know those old Getrag manual gearboxs could be a little 'reluctant' on shifts more so when cold, having owned them when newish, so would be 'nice to have' feature.

hope this helps

 

Thanks iconic....and no it doesn't hang at high rpms when revved in neutral while stationary....I don't have cruise control and my experience of switches attached to clutches was only to ensure the clutch was depressed in order to start it...never had an English Euro or Jap manual car with that but had corvettes and mustangs with this feature ..it being something of a US safety legislative add on perhaps

The conversion on this car was done a good few years back and The auto ECU was tricked into thinking it was still an auto making manual changes by making some sneaky connections here and there.....now if all that sounds vague its because I don't yet know how it was tricked....but the ECU was not reprogrammed to a manual format.

However the way it is now was not how it used to run and was a point highlighted to me by the seller who did the conversion....simply as a high idle....well its a bit more than that

Problem is that talking through how things were tricked with the seller isn't as good as pointing at the wiring that did the trick but unfortunately the previous owner is a long ways away and at time of purchase he was not sure what the problem was....he also had not driven it any distance in it for a while so im not sure he even knew of the the high revs neutral condition....

But something as unrelated as vehicle speed causing an engine to rev which, to all intents and purposes is detached and independent from the car in neutral with neither clutch or accellerator pedal depressed, would indicate some speed sensor sending a signal to fuelling resulting in this revs surge as soon as the car rolls past a few mph....and as far as I know the wheel speed sensors only work with the ABS system

It may not be related but I should have tried the roll in neutral experiment on my auto X308 XJR to see if the revs climbed....a positive result would indicate that its an auto ECU feature and that my X300 has lost its trick....probably nothing more than a loose connection for what normally tricks it.

Ah well....the story so far and nothing I can do with it until I'm next home at which point I'm going to strip the whole intake throttle body, idle control valve,and fuel system for a clean down....but I won't be happy if I do that and it still has this neutral rev problem

Hoping for XJREngineer to chip in with this weird one.....as I'm pretty sure that the solution is probably going to be Andy doing a remap of the ECU to make it fully manual compliant...any time Andy !!! ��

 

Thinking about this some more, the 'syncro enhancer' system (if fitted) must have a clutch pedal switch to work properly.....or you couldn't ever drive below 2000 rpm!

Doh!

We can assume she must have a clutch pedal switch somewhere.

What happens if you coast in neutral with brakes lightly on so the brake lights come on.....?

 

Can't say I drove like that intentionally but did long soft brake while in neutral and it didn't slow the revs while still in forward motion.....only when I came to a total stop

I will be looking for switches on the clutch pedal when im next with the car but it still doesn't obviously explain how the revs rise when I rolled down a short slope in neutral from stationary....let off the hand brake and as soon as it got to walking speed the revs picked up .....then I coasted to a stop and the revs dropped....all in neutral and without touching any pedals

 

"but it still doesn't obviously explain how the revs rise when I rolled down a short slope in neutral from stationary"

....because there is a speed input going to the ECU..then going to the idle speed control unit?

 

Yes ...Has to be the reason...now I just have to dig in and find the idle speed control valve 'stepper motor' when i get onto the throttle body and either clean it or replace it .... I might expect the synchro assist to raise my revs to say 1500 but the 2500-3000 I'm seeing just isn't right....especially when it hangs at that speed for so long between shifts and for a few more seconds than it should when I come to a stop....and if that doesn't work I will see if I can disconnect the synchro function completely providing it doesn't mess up the running....as I said previously its not something i am used to on a manual car where I much prefer heel toeing the revs the way I want to

Thanks for you input Iconic......its helped me

 

2000 to say 2500 rpm sounds about right, my S type hangs around this rpm and if you work out change points this would make sense.

Thinking on my feet here, it will 'hang' the revs until the clutch pedal comes back up as the ECU will not know the shift has occurred...the clutch pedal switch is the 'driver' as such...on a really cute systems the vehicle speed input can vary the 'between shift' idle rpm to help shift quality.

I've just sold my S Type manual so can't be more helpful....

Cleaning the idle control valve and throttle body is always good practice though...I cycle the ICV with 12 volts whilst using WD-40 to clean out the muck...WD40 seems to work better than carb cleaner for me on the IAC's maybe being heavier it soaks into the carbon a little easier and WD40 even does a good job of the throttle body too at a push

good luck

 

heel and toeing and left foot braking...thats how my Satira GTi is driven 'round Snetterton!

 

I'm skeptical of the much less computerized X300 having the electronic sophistication of your S-Type with regard to all these sensors; there are reports of automatic XJRs having similar issues with holding revs without touching the accelerator, and much evidence from those cases points to a dirty throttle body being the ultimate issue. That being said, good luck getting to the throttle body in your XJR; the labyrinth of intercooler and supercharger piping means it's going to be quite a struggle to reach it. I tried accessing it last weekend and could not get to it from the top of the car; I'm going to have to try and do it from underneath.

 

" good luck getting to the throttle body in your XJR; the labyrinth of intercooler and supercharger piping means it's going to be quite a struggle to reach it. I tried accessing it last weekend and could not get to it from the top of the car; I'm going to have to try and do it from underneath."

Yea Its not an easy job... I have read of the underside approach but I don't fancy lying on my back doing it....but suppose the alternative is breaking your back leaning over it....however it will give me a chance to detail all those crud filled spaces under the supercharger intercooler.

I have to admit to thinking the X300 wouldn't be as smart as an X type when it came to handling revs between shifts but I guess you never know until you try to find out why its doing something like mine...and as said mine has an auto ECU running the clever stuff which normally does not work when used on a manual car without being re programmed....mine hasn't been programmed and it the car has no loss of performance.

Here's hoping its as simple as an idle control valve stepper motor....but not being with the car I'm supposing that's going to be almost as hard to get to on the Xjr as the throttle body...

 

Me and my car are not best of friends because of this strange rev behaviour.....had the stepper motor replaced......throttle body cleaned....... Still holding high revs for about 5 seconds when coming to a halt....revs still climb when I roll down a hill in neutral and feet off pedals.....this has to be the ecu/speed sensor in hubs related....any other ideas??....or can someone chip in that has a manual and tell me if theirs does the same....I wouldn't buy a car new that did that....never had a manual car that does this

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In Andy's widely read thread
XJR6 Engine ECU Successfully Remapped
he mentioned that X300 has an "adaptive throttle" which in your case may have been inherited from pre-conversion times, and the car might fall into limp mode as it fails to detect the automatic transmission. Other problem that I read from this forum is the engine may stall at the lights. A few pals here have had their ECUs remapped by Andy after the auto-to-manual conversion, and are happy with the results. You may wish to email Andy directly and see if his remapped ECU is indeed your solution.

 

The AJ16 engine ECU does not contain any software intended to raise engine revs during manual gear changes. The ECU does contain software that disables closed loop idle speed control above a very low vehicle speed threshold. I can't remember exactly the speed, but it is consistent with your observation of the revs changing as you pass above or below "walking speed", so maybe about 5mph.


Here is how closed loop idle speed works:


1) the ECU must "think" that the throttle is shut before attempting to control idle speed. This decision is based on the throttle potentiometer signal being less than a value that the ECU has previously learnt. This learning process can be affected by changing ECU or throttle bodies or potentiometers. None of which is relevant in this case. However, just be cause the ECU "thinks" the throttle is closed, it doesn't mean that mechanically the throttle blade is fully closed.
2) the vehicle must be below the vehicle speed threshold, which I can't remember for sure, but think is 5mph


When the closed loop idle speed control (ISC) strategy is working, the ECU controls the position of the idle speed control valve to "try" to maintain a target speed. When the engine is fully warm, this would be 690rpm in a standard manual XJR, 650rpm in an auto in neutral and 550rpm in an auto in drive.


When the ECU is not trying to control the engine speed, it will position the ISC valve in a position that it thinks will provide the correct airflow to maintain the same idle speed as the target value, but it is just a "guess". The ECU DOES NOT simple leave the ISC valve it the position that provided the target idle speed when it was in closed loop mode. This is why the engine speed sudden jumps when the car rolls above 5mph, wit no foot on the accelerator. It just means the "guessed" position for the ISC valve is too far open for the prevailing conditions.


From your description it sound like your idle speed control valve is working because the ECU is "trying" to control the engine speed when vehicle speed falls below the threshold, say 5mph. However, the position that the ECU moves the ISC valve to when not in idle speed control mode provides to much air. I suspect that this is because the throttle blade is stuck ever so slightly open. It is still closed enough that the throttle voltage is low enough to trigger closed loop control when the vehicle is below 5mph. However, when the clutch is dipped between gearchanges and the vehicle is above 5mph, the combined airflow round the throttle plate and through the ISV valve gives the engine speed of 2500rpm. Has the problem got any better after cleaning the throttle body?


This vehicle will have an additional problem because it is a DIY auto to manual conversion. The ISC valve position that the ECU "guesses" is more open for an auto in drive than for a manual car, due to the drag torque of the torque convertor. It is unlikely that a DIY conversion will ever drive like a factory built manual XJR, unless it is fitted with an ECU for a manual XJR. These ECUs are extremely rare but I know someone who has one.