Hi Guys, a new fault has developed. I hope you can help. First noticed idle rpm was a bit high - 1100. Then noticed on deceleration there was little engine braking, the vehicle did not want to slow down at about 35 mph. I also noticed when applying accelerator there was about half a second delay with a big kick up the back side when it kicked in. like a sloppy uv joint on the drive shaft, but this is a recent aberration so I know it's not that. Also this happens when I let my foot off the accelerator. I then noticed when at rest if I rev the car, the rpm climbs then drops and then without me touching the accelerator it climbs again to 2500 rpm on its own then goes back to 1100 rpm. I have recently replaced everything I could for the old fault missing when warm. I just went for a ride from cold and noticed that these symptoms get progressively worse as the car warms up.
crank position sensor, throttle sensor, idle sensor, coils (5 nos. and 1 used Lucas made in Japan), fuel pump and filter, fuel regulator and 4 O2 sensors.
Any suggestions will be gratefully received. Thanks in advance.

 

The engine ECU is modulated by the transmission ECU to coordinate their activities as they dance together

The transmission ECU is communicated " to " by the transmission speed ( shift points ) sensor located inside the transmission body

The shift solenoids inside the transmission are communicated or commanded " from " the transmission ECU

So a quick and cheap check would be the connector on the left rear of the transmission body with the wires pointing aft

This connector can get contaminated and cleaned without jacking the car

This connector comes off by pulling straight back 1/4 inch and only then rotating the barrel , it aint normal

Since the connector is buried in the casting walls tiewraps will aid in rotating the barrel

Another contributor posted these excellent pictures

The next step would be to put a meter on the TPS

 

Thanks Parker, the transmission connector was spotless, I also took a look at the ecu connections as I hear they are prone to water ingress and rusting. they are also shiny and spotless. So now to the TPS, how do you take a reading ? I can get to the loom from underneath, so which wires ? and do I do it with ignition on or not ?

 

The TPS has the return wire to the ECU as the middle wire on the TPS connector as color Green / Yellow

since the TPS is under the TB you can follow the wire up and over the fuel rail and nick the wire insulation

What you want to see with the engine not running but the key in the run position with the TPS connector connected

At the idle stop you should see 0.60 volts DC and you have to use a very accurate meter

Very very slowly open the butterfly and the voltage must smoothly increase toward 5.0 volts which is the reference voltage,; you will never see the full 5.0 volts

What you don't want to see is a spike to 0 volts as this would be a bad spot on the wiper on the windings

alternately you can read the TPS in a different way from the ECU connector as resistance through the TPS

Red 12 to red 7

What you don't want to see is the resistance spike to high during the sweep , it should smoothly decrease in resistance

 

Thanks Parker for the reply's. I'm not sure how accurate the multi-meter is but I appear to be getting 0.75v on tickover and 5v on full throttle. I will go and buy a digital multi-meter and swap out the TPS for another one I have and give you the results later. If the readings are correct do you think I should take it to have the TPS re-calibrated at Jaguar ?
Ok just got a digital one, at idle it reads 0.76v and full throttle 4.76v. I have another TPS around, I will switch them over tomorrow and let you know the readings. The surging seems to be getting worse, it's like the cruise control is kicking on and off even though it is off. Let me know your thoughts.

 

Do not swap the TPS until you have a understanding of it and how critical the idle position reading is

On paper the idle stop position is 0.60 + or - 0.02 volts DC

 

So what could be altering the voltage ?

 

Unless the TPS has been previously reset via PDU, WDS, etc.

Regardless, your TPS seems abnormally high. Even for a reset sensor. Either the butterfly is not closing all the way, or someone adjusted the stop on that throttle body, again, preventing it from closing. That throttle body should come off. Clean it, both sides, and then check the clearance of that butterfly. At closed, it should be .002". If that's all right, then I'd start looking at a new TPS. Perhaps the sweep is worn down?

 

I measured the voltage of the TPS admittedly it is on the high side for tickover, which would account for the 1100 rpm. My problem is surging on declaration, the voltage rose consistently to nearly 5 volts. This should not cause erratic deceleration in my opinion. So where do I go from here ? Any thoughts ?

 

Yes , you are correct

Your term kickover may not be the best testing period for the TPS

The ECU feeds the TPS a very controlled 5.0 reference voltage to the TPS and other sensors

This broadening out to the other sensors the reference voltage wire is spliced into is more than one thing at a time to keep track of in troubleshooting as the others may be effecting the one focused on . so we stay focus on the one

normally a separate device or sensor will suck down a tied into device but your reading at idle is otherwise as a higher then normal TPS return signal reading ( in your information ) would require a biased higher then the target reference voltage

In the engine starting sequence the ECU regulation of this reference voltage may not be best until the total cars voltage is stable so a TPS reading may not be valid until the interaction of a drained battery during start and the higher then the battery normal 12.75 charging by the voltage regulator in the alternator has stabilized

The normal voltage on a stable X is 13.5 to 14.5 but the question is the transition period and if the reference voltage can keep up with a changing voltage supply to work with

In one case the voltage regulator would totally drop out during deceleration so the voltage the ECU has to work with suddenly changes from 13.5 or sorts to 12.75 the battery voltage

This would not be the case if the TPS reading is during a non - running engine , just guessing theory wise

There have been cases where the voltage regulator ( IN435 ) has not been stable on deceleration and are easy to source and change yourself

This would be a separate area of engine operation regime then the starting sequence that you are possibly testing at to derive your information

As long as you observe a smooth change in voltage through the throttle range your TPS should be OK except for the idle range which is still in question

But you can skip the TPS for now and look at the IAC valve coming into play on deceleration

Do not remove the IAC valve yet ( bolts can snap off ) and the IAC valve does not have a followup position sensor like the EGR to see a error between the commanded position and the actual position

But......

The IAC valve is not full open or closed but modulates between during your drive

It is a 4 wire stepper motor

You may not see a fault as a open leg with a meter on the black ECU connector until the stepper motor is warmed up and the windings thermally expanded or by tapping on it

This is a good time to inspect the ECU connectors for corrosion and missing tabs on the 2 tab female sockets ( This is a common item on the X300 and sockets easily available )

You should have some spare sockets in the connector if I remember

 

This is the problem, I took the car up to 50 mph then foot off the accelerator completely.

 

I have 2 spare IAC valves, I will try another and let you know the results

 

the IAC bolts are Loctited in so they have a habit of snapping off

You can apply heat to the inside of the TB to loosen them up , more work

The IAC bolt heads are a 5.5 mm hex

Someone had a synchronizing procedure to exercise the IAC valve system

 

Thanks Parker, so no problem with the bolts switched out with a spare. Problem still there, slight increase in tick over with this one ?

 

So I do have another which I will try, but failing that I will buy a new one. I have found a large price difference between ones offered, would this one work ? Replacement 1997 Jaguar XJ6 L - Idle Control Valve REPJ313203 (carparts.com) or should I buy the dearest one at 110 bucks ?

 

The term kick over , are you referring at the point of engine start cycle or after the engine is started after a warm up period with the throttle in the idle position

The TPS test can be done with the engine not running

If the TPS reurn signal is above 0.62 volts at the butterfly idle stop that is high

There are things to keep the butterfly from returning to the idle stop that can be addressed

Do not adjust the idle stop inside the TB yet and you probably will never have to

as you relax on the pedal the butterfly may not be mechanically returning to the idle stop and the ECU is calibrated to operate the IAC assuming the butterfly is closed as a full relaxation of the pedal , this would be different in a partial relaxing of the pedal

There should be a rate of change of the TPS value the ECU monitors beyond the at the moment position value

Do you have available a ELM - 327 based tester . The TPS will never show below 13 % on the position of the butterfly even thought it will be fully closed

This has to do with the engineers reference point of absolutely no air flow through the TB but the IAC is partially open after it settles down from a far open to the decreasing down to the idle speed target

 

Tick over is what I meant, warm engine at idle. I recently did connect odb11 software but only got rpm at idle on live data, this showed 950 rpm at idle even though the tachometer was showing 1100 rpm. I will try again and look for a percentage reading. Thanks.

 

Idle should be .......

see page 90 for list.but generaly you will hear 650 assuming they are in gear other then park . its complicated

You should be on OBD 2 and if on 1 there may be a error on reading the data bus correctly as there are different data bus protocals through the years

see page 89 for IAC information

The % reading is not realty necessary as you have the voltage in which the % is derived from measured and we have to use the voltage as a reference unit of measurement

The book value is in volts only for the idle stop position

Giving out the 13 % is a odd value you would not expect if you saw that but again not necessary to see since you have the voltages

www.jagrepair.com/images/Training Guides/801S - 2000.pdf

 

error

 

Now we come around to the reasons the butterfly may not be returning to the physical idle stop

some have found the throttle cable miss routed or binding or the return spring under performing if the original factory spring is present ( there is a way around acquiring the revised stronger spring ) _

There is 2 A and M marked mounting positions just before the inter cable attaches to the butterfly bellcrank , you may not see the A and M because of the surface age

Then the question on the part # of the EGR valve installed and if it is being controlled correctly with the correct PROM

The EGR ( the EGR has a EGR_ error parameter ID on the ELM - 327 and the target value is 0 as live data but is not perfect ) as well as your EVAP valve ( can be tested with a 9 volt battery ) should be closed at idle

05.1-26 amend4 (R493) (jagrepair.com)