This is another episode of Rose's recovery after gearbox conversion from auto to manual and 3-years' coma.

Rose runs very well after recovering from three years' coma, as she has been a new ECU, new CPS, new fuel pumps, cleaned fuel tank, cleaned fuel pipes, new fuel filter, cleaned fuel rails, new injectors, new plugs..... She now drives like a dream. Torque is so strong that often time she runs at 4th or 5th gear, and stays there even at low as 1250 rpm. She cruises effortlessly at 100 km/hr at 2000 rpm, or 60 km/hr at 1500 rpm; and flies like a rocket when I floor it. However, at cold start the rpm is typically initially 1250 rpm, then level off at 1000 rpm after 2 minutes' warm up, and after reaching operational temperature through normal driving, at the stop lights, the engine's idle can go up to 1400 rpm, and drops slowly to 1200 1300 rpm.




At present, there is mid to high air leak from the cracked exhaust manifolds
(stainless steel replacement pending). I visited a local Jaguar workshop and the mechanic helped scan my engine. His Autologic Bluebox detected the following DTCs:



Some of the DTCs seem conflicting, but the workshop in-charge advises that it is very difficult to adjust X300 especially the supercharger model because the idle control valve is situated under the supercharger pipes and hoses, and I might as well replace the idle control valve. My other mechanic who helped rescue Rose from death was also wondering how to adjust the engine idling speed. I intend to tackle this after fixing the exhaust manifolds (which might result in removal of the EGR valve and, possibly the front cats), but any heads up on possible causes for high idle meanwhile, or any advisories on potential technical consequences of removal of the EGR and front cats would be welcome.

 

With the new ECU, you need to do a throttle adaptation. Instead of slotted screw holes on the throttle position sensor and adjusting the TPS until you get a specified voltage, the X300 has a learning procedure when it takes whatever voltage the TPS puts out at when you do the calibration, defines that as closed throttle idle and then it knows what idle voltage is.

I suspect that your ECU isn't calibrated, thus it doesn't know that it's at idle and therefore isn't adjusting the idle speed motor.

You need to do a Throttle Adaptation, and you need a dealers computer to do that.

Or, as a work around what some have done is go back to the old way and cut slots in the TPS and twist it until the idle comes down. However, that's very difficult to access on an XJR, I'm not sure if it's even physically possible. Also, TPS are amazingly expensive for these cars for some reason.

 

If you remove the cats it will always have a check engine light on. X300's are unique, in that the downstream O2 sensors (the one after the cats) is the main one that adjusts the fuel mix and the upstream one (closest to the engine) is the check for catalyst efficiency. This is reversed to every other car I know of, and I have no idea how they make it work, but they do.

So I would proceed with caution in removing the front cats anyway. You can remove the underfloor cats with no effect on the engine management, they won't know if they are present or gone.

 

Rose just passed the 1st stage of recovery, where the priority was to wake her up and enable her to pass the government roadworthiness test. This primary goal has been achieved and my mechanic and I now proceed to the second stage of refinement: idling is one of the areas needing investigation, clearing DTSs and dash warning lights, fixing clock/radio/odometer LCD display (see my other posts), etc.

I do not know if the new ECU has been calibrated, but would believe Andy might have done so as he also incorporated the timing advance by reprogramming the ECU, and tried it on his own XJR before sending to me. However, if this is standard procedure upon in-car installation then this indeed was not done on Rose, and can only be achieved with factory scanner-computer. The Jagaur workshop that I have my engine scanned did not mention this but pointed out that idling can only be adjusted through the Idle Control Valve hidden under the Supercharger housing, hoses, etc. However, I have reasons to doubt his advice as I have more confidence of the knowledge and sharing available in this forum, and in my own mechanic although he rarely handles Jaguars but German, Italian cars and vintage cars.

As for the TPS, my understanding from reading this forum is that it only needs re-adaptation if removed or replaced?

As regards the front cats, some folks in this forum claim that they often have them removed to achieve better performance, and some factory downpipes don't have the front cats. However, Rose's probably have Japan-specs and so only has two O2 (on the downpipes past the front cats) rather than four. If the stainless steel manifolds I custom-made from the UK wouldn't fit and I have to be forced to remove the front cats, I plan to fool the engine management system by re-locating the two O2 sensors to the floor cats. However, this would mean that the reading distinctions between the two banks of cylinders would be lost as the exhaust reaching the floor cats has run past the 'Y' pipe. Nevertheless, I think I would accept this, as I want a more permanent solution for the cracked and otherwise new but expensive factory exhaust manifolds.

 

Think of the ECU and TPS as a matched set. Once calibrated to each other they work together, but if one part is replaced then both the existing and the new part need to be calibrated to each other. Sometimes you just get lucky and the calibration of the new part is the same or close enough to work fine, and other times it isn't.

But in this case, the calibration has to be done "on car", it isn't something Andy could have done in his workshop without your car.

There are those of us who have cloned the dealer computer tool to do this calibration ourselves, there is a big thread on that here.

Your workshop isn't wrong in saying that the idle control valve control idle speed, that is true. However, it only works at closed throttle, so the ECU isn't adjusting the engine speed while you're driving. To do that, it needs to know where closed throttle is, and that's what the throttle adaptation does. If the ECU thinks it is not at idle, it will not activate the idle control valve and will make no attempt to control idle speed.

 

As a second thought, can you plug in an OBDII scanner and see what the readout of throttle position is? It should be about 12% or so at idle. There is an adjuster in the throttle cable (and another in the second cable if you have traction control). That adjuster can control how tight or loose the throttle cable is.

If you have traction control, there will be a cable from the gas pedal to the traction control actuator, and another from the actuator to the throttle plate. Each will have an adjuster and sometimes to you have to adjust both to get the full range of travel from fully closed to fully open.

When I got my XJR the cables were badly adjusted and I think it only went to 57% throttle with the pedal to the floor! After adjusting I was able to get it to go to 98%. My first step would be to slacken the cable right off and see if your idle comes down. It's possible the cable is too tight and it not letting the throttle fully close. That would overwhelm the adjustment range of the idle control valve.

Assuming the cable does let the throttle fully close and you can successfully reduce the idle, then watch the throttle position as reported on the scanner and start taking out the slack at the adjuster slowly. Listen for any change in engine speed or if the scanner reports an increase in throttle opening. Then with the engine off, push the pedal to the floor and see if you are getting close to 100% throttle.

If fully slackening off the cable to ensure the throttle is closed has no effect, then go to the throttle adaptation reset.

 

Yes, Rose, being an XJR, does have Traction Control.

My mechanic has previously tried slackening the throttle cable but this failed to lower the idling. My ELM 327 also has limited scanning capacity when used with my iPhone - it does not support O2, ABS, Airbag reading (see my other thread https://www.jaguarforums.com/forum/xj-xj6-xjr6-x300-26/dash-warning-signals-177166/) Hence, I turned to the workshop that has Jaguar-specific scanner, and got the codes mentioned above. Maybe I should return to the shop for a more detailed check on O2 readings as well as the throttle position.

 

Here is an update. Went back to the Jaguar workshop and asked the shop ic to run the scanner again to check on O2 reading etc., and ask if it was possible to calibrate the new ECU with the Throttle Position Sensor (TPS) or the two new O2 sensors (NTK, bought from RoackAuto). However, was told that his scanner (Autologic) could not read O2 (???)..... it has to be the Idling Speed Control Valve (ISCV).... which cannot be reached except with the Supercharger removed in which case I better have a new ISCV ready ..... Oh dear..... I can forget about this shop; it has the right tool but not the knowledge to use it well). I might as well go back to my Alfa guy who has successfully rescued Rose and put her back on the road. The only trouble is we lack the right scanner. Said it before, tried iCarsoft i930 but it did not read Rose at all, and the ELM372 does not read Rose's O2, ABS and airbag system.

Anyhow, I have been researching more on high idling cases, and tumbled over this thread.
https://www.jaguarforums.com/forum/x...ine-ecu-36179/
I wonder whether
(a) it could just be the throttle body needing a good clean up.
(b) I need to find another shop with the right tools to calibrate the new ECU with the TPS, ISDC and O2 sensors
(c) it could be the engine temperature sensor playing up - the idle speed keep going up, from 900, 1250, 1300-1400 rpm. The longer the drive the higher the idling, plateauing at 1400.

 

A throttle plate cleaning can never hurt, but it's not easy to get to on the XJR. The XJR is less prone to throttle sticking than the normally aspirated cars. The reason is the throttle shaft orientation, it's horizontal on the XJR, vertical on N/A.

What happens with the normally aspirated cars is the crankcase vent is just ahead of the throttle, so it's sucking all the oil fumes through the throttle. If you do lots of short trips in cold weather the oil fumes are sticky and attach themselves to the throttle plate and run down the shaft into the throttle shaft bearing and then gum up the shaft so it can't rotate freely.

I had that happen to my 95 VDP. After a bit of freeway driving at 100 km/h I took my foot off the throttle and the car didn't slow down. If I put it into neural and blipped the throttle aggressively and as quickly as I could it would slam the throttle shut and idle came back to where it should be. In my case cleaning didn't help, replacement was the only cure.

Regarding your point c), what happens is a cold engine needs more air than a hot one, mainly to overcome the friction of the thick oil when it's cold. As everything warms up the engine needs less air to maintain a given idle speed - that's why there is an idle speed adjuster, to cut back the amount of hot idle air.

Your car is showing perfect symptoms of the idle air adjuster not moving, which is related back to the TPS orientation in the thread you linked to. The ECU is not seeing a closed throttle, thus will make no attempt to adjust idle speed.

I believe the idle air valve is a standard GM part, it certainly looks like the one used on lots of GM cars. Not that it helps you, since I doubt there are many GM cars in Hong Kong!

 

I had the exact symptoms on a NA 95 VDP and it had naught to do with oil in the throttle shaft or plate: It simply needed the throttle spring TSB executed. Same issue later on a 96 VDP, same cure. I don't recall if the TSB's applied to the supercharged cars or not.

 

Mine had that, didn't fix it! A new throttle body cured it. The old throttle shaft was noticeably harder to turn by hand than a new one when I had them off the car.

 

Hi Marcus,
Jagboi64 is absolutely right. I could not set the throttle adaption on the ECU that I reprogrammed for you. I tested the ECU by connecting it to my own car. The ECU software will learn the closed throttle voltage on my car, if it is lower than the previous car to which it was fitted. When the ECU is fitted to your car, if the closed throttle voltage is higher than my car, then the ECU will not recognise the throttle as closed. The ECU will not try to control the position of the ISC valve in order to control engine speed. This is just as described by Jagboi64. There is no mechanical adjustment possible of idle speed, assuming the cables aren't too tight, the blade isn't jammed partly open and the ISCV isn't stuck partly open. The most likely solution is a throttle adaption, as previously suggested. The good news is that the function is available on Autologic equipment. I know because I have personally used this function on this equipment. The bad news is the people that you are dealing with don't seem to know how to use the equipment that they have got. Assuming their equipment is configured for Jaguar X300, I suggest that you encourage them to search the menus until they find throttle adaption. I know it is there. I am almost certain that this will fix your problem. Then you can really enjoy your manual XJR conversion.

 

Thanks, Andy. I would try making another visit to the Jaguar workshop. One main reason why Jaguars have very low resale value in Hong Kong is high cost of parts and lack of independent Jaguar specialists. The dealer is not for everyone, and the Jaguar workshop I mentioned is hopeless as the people there (two before, now left with one after the more experienced guy retired) lack the language proficiency to benefit fully from the many on-line resources, TSB's, forums, and YouTube tutorials, etc.

I hope adaptation would fix the idling issue. Rose is the most satisfying car I have ever driven, but is yet to be tamed and refined. It runs only 6 Km per litre right now, which is kind of low (new pumps, new O2 sensors and new injectors though), and CO emission is 3.5% to 4% at idle.

 

Just to close this thread when other issues arise. Throttle adaption was finally done and fully resolves the high idle issue. The engine now idles beautifully at 750 rpm. Rose's post-recovery issues continue in another thread - Dash Warning Signals.