Hello,

i need some help with my 1996 X300 with 4.0 AJ16 Engine.

The Issue:
- poor and rough idle when the engine is warm or hot (< 600 rpm)
- no problems when the engine is cold
- absolutly no problems with accelerating
- sometimes (in very very rare cases) the engine interrupts while smooth cruising with 2000-2400 rpm
- no error codes
- no stalling

A few days ago i replaced the lambda sensors due to the high fuel consumption.
The result:
- reduced fuel consumption
- the idle issue is getting worse
- sometimes, after 10 seconds, the poor idle is getting better (>700 rpm)
- the interrupts while driving with constantly 2000-2400 rpm are increasing
- acceleration without any problems (at once i accelerate, the engine is running fine; it seems that the engine is getting no enough air or fuil while idling)
- no error codes
- no stalling
- The exhaust emission check is done this week. so the new oxygen sensors are working fine.
- the short term fuel trim somtimes goes up to +25% (to lean?)

I checked and replaced the spark plugs. They are as they should be.
I replaced the ignition coils. Makes no difference.
I cleaned the throttle body and the idle speed control valve.

Any ideas??

Some supplementary questions:
- If i take off the plugs of the oxygen sensors or the idle speed control valve while idling, there is absolutely no difference. Why not?
- the idle issue is getting worse after replacing the oxygen sensors. Why?
- if i take off the plug of the air mass sensor, the engine stalls

what can i check next?

What about
- camshaft sensor
- crankshaft sensor

thank you for any help

Joern

 

Throttle position sensor, or TPS is where I'd be looking. There are a multitude of posts about it and a search will unearth them. On the plus side, you have eliminated a number of other possible causes.

By the way, I just noticed that you are in Germany and as I get to Hamburg fairly often, I imagine that you are in something of a minority. I've only ever seen one xj there and it was on UK plates!

 

With everything you have done to this car, you really need to have three things done with the Jaguar Diagnostic equipment.
1. Throttle Adaption reset
2. Oxygen Sensor Orientation run
3. Reset the ECM Adaptions [listed as Reset Adaptive Terms in the diagnostic menus]

When disconnecting the MAF, the engine should stall. If it doesn't, it wasn't working.
Ignore that last statement regarding the AJ16 MAF -- See post #10 for my mea culpa!

When disconnecting O2 sensors on the AJ16 you normally don't see much impact right away.

You replaced an O2 sensor, evidence does indicate the original had failed. That means the engine has been running who knows how long with that failed sensor. The ECM and adaptions have been trying to correct for that failure for the same 'who knows how long' period of time. Now it's fixed, and it's still adapted to the bad sensor; that's why the three above items need to be run. Though I should say, the throttle adaption is really required because you have tampered with the throttle body when it and the IAC were cleaned.

Big problem is, you have to find a dealer that still has some of the old equipment in working order, not to mention someone that knows what we're talking about.

Good luck!

 

Hi,

yesterday i looked out for some airleaks...and i found a disconnected vacuum line (one side was connected to the inlet manifold...)

Not easy to figure out where i had to connect the other side.
Today i lifted the car and could find it: it seems to be the line to the pressure control valve (CBC7714).

After connecting it, i did a testdrive an...now i'm happy :-)
The idle is ok an i can replicate the issue by disconnection the hose at the inlet manifold.

@xjrguy: i'll do the three mentioned points next time by my dealer

@sogood: yes, the X300 and X308 are quite rare hier in northern germany. one of the reason i love the cars :-)
A friend of mine lent my car for his marriage last year. So he had to buy one for himself a few months later :-)

thanks for your help!

Joern

 

Uh oh.

Mine stays running ...at least at idle....when the MAF is disconnected. No reaction from the engine at all other than the STFTs chaging pretty quickly

No CEL either!


Cheers
DD

 

Glad to see you go it sorted and that it was an easy fix. That's always a major bonus. An air leak had occurred to me (fleetingly) until I thought it was too obvious! Lesson learned, always start with the simplest, basic approach and work your way up.

Happy motoring!

 

XJaguar,

or anyone,

Is that hose in that spot on all aj16 engines that are not supercharged? I do not think mine has that . I will definitely look tomorrow.

also does anyone have a slightly better more zoomed in picture and like a routing diagram?

thanks

 

Hi,

here are two better pictures.

On the second pic i marked the dipstick tube for the automatic transmission for better orientation (mine is wraped due to a leak).
It's difficult to find. I took off the dipstick for the engine oil.

The picture above in #4 is from an earlier X300 (4.0 Sovereign, too). Both of my x300 has that hose.

 

Thanks man,

i looked last night and that hose is definitely hooked up, but great info for others on the forum.

thanks for the excellent pictures.

 

Geez! My apologies guys.....

Old age settin' in. I shot from the hip Saturday and confused the last AJ6 with the AJ16. Back at work today and checked some notes.....
The AJ16 ECM is quick enough to plug in nominal values for the MAF and ECT to catch and stay running when they are disconnected. Slight impact to idle and throttle response will be noted.
The AJ6 will stall, and then the ECM will plug in values at restart so it will run; albeit at high fuel consumption.

Sorry for the cornfusion!

 

Hello,
I found out this thread when looking for a solution for my 1996 XJS who has exactly the same symptoms:
- rough idle
- interruptions when cruising 2000 / 2500 rpm
Has anyone an idea where the other end of the vacuum pipe is connected on an XJS?
Thanks,
Pierre

 

Cracked exhaust manifolds or a bad donut gasket seal as the manifold goes into the down pipe allowing high O2 fresh air to be sucked in between pulses biasing the O2 sensors to see a too lean STFT so it goes rich . Easiest thing would be to back off the donut flange bolts , lube , then retorque . Inspect exhaust manifolds after removing cover . Pierre77N , AJ16 engine starts on page 51 and may have some information for you . The inboard aft nut needs about a 15 degree offset so i just " set " the extension into the 15 mm deep socket without fully inserting it to get the 15 degrees . What I found on mine was that I had both a cracked manifold and a damaged flange on the downpipe side that the donut gaskets seats into . I wouldn't recommend totally removing the down pipes as it is not easy to put it back together ( at least on mine as it was out of shape ).

Your " interruptions when cruising 2000 / 2500 rpm " may be a separate issue .

http://www.jagrepair.com/images/Trai...20-%202000.pdf

 

Interruptions at cruising speed usually indicates an issue with the TPS. Not a cheap part, however not an entirely uncommon problem, so I’m pretty sure that’s going to be part of your problem, and possibly an initial stumbling block to fixing whatever else could be wrong.

You’re going to have to replace the TPS and then using some Jaguar specific software, reset the TPS setting. The only other possible solution is to get a reading of the TPS now and try to match it when installing the new one.

In theory, that should work, but I’m not sure anyone ever went through the issue to replace it that way. You’ll need the volts reading when the TPS is at rest. Should be at 0.6v or very close to it.

Once you’ve resolved the faulty TPS, we can start diagnosing other problems, but this could be the only problem you have.

 

With the key in the on position , not running , slowly open the throttle and watch the 0.60 volt change . A bad TPS has the wiper arm lift off the resistor windings as you sweep through the range so you will see the voltage bip to 0.0 on a bad spot . You would read this on the Green / Yellow wire

You can also watch the TPS with power off by reading a resistance value at the ECU connector as it sweeps through . A bad sensor spot will bip to high resistance . Read pins Red 12 ( TPS return signal ) to Red 11 ( 5.0 reference voltage from ECU when powered )

The TPS sensor position relates to the RPM based on the engine load , as it finds the bad spot , if that is the case .

Before you remove it get a original reading at the idle stop with either the voltage or resistance method as this may negate a ECU reorientation , In theory .

 

Thanks for the input. I will actually try to test the TPS.

 

Sorry for the dummy question, but how do you mesure the 0.6 V? Do you strip the green / yellow cable?
Thanks!

 

Another one...
I can have another TPS coming from a X300.
Could it happen that the car doesn't start any more if I just swap both TPS's without the software?

 

You can do the second resistance test by pulling the connectors off the ECU ( located by the right foot of the right front seat . The map I made is of the connector view . Look for common corrosion on the 2 large connectors .

The voltage test can be done on the wire ( Green / Yellow stripe ) as it comes back over the fuel rail under the narrow plastic cover . Otherwise the sensor connector is underneath the throttle body so it's hard to get to .This would require stripping the insulation off a bit just enough to touch the wire with the meter lead .

One easy thing you can do is to reach under the throttle body and ensure that the sensor connector is clean and secure ( with the clip engaged ) as mine was not . It is in area that gets contaminated with oil .

The value that you should read at the idle stop is 0.60 + or - 0.02 volts and to match the exact current value that you have in that range with one you replace it with ( if you do so ) is an attempt to not have to do the ECU reorientation .

What I found with mine was I had to drill the mounting holes on the plastic sensor larger to be able to twist the final mounting pressure to get that 0.60 volts .

Any questions , just ask .

 

Thanks!
I will try this tomorrow.

 

Well...
I've tried another way and before doing anything with the TPS, I changed the coils with coils from another car and... she runs fine now!
Thanks for your help!
Pierre