Even since I bought my cat it has a very strange behavior after starting the engine cold and at cold weather. It always starts from the first try, even this morning at -26C and immediately increases the RPM up to 1200 - at this moment the engine is working very smooth. After about 30-60 seconds the RPM drops to about 800 and that's when it's becoming unstable. It seems like one or more cylinders are not working, but we did a check at a garage (by disconnecting the spark plugs - one by one) and we've discovered that all cylinders are working properly. The spark plugs are brand new NGK iridium, the part-load breather is clean, the MAF is clean, the throttle body is clean as new, the air filter is new, the engine oil is new and proper for the cold weather...
For me it appears that the rough work of the engine is very similar to an air leak (absolutely the same symptoms as when the part-load breather was disconnected) but I double checked everything from the air filter up to the throttle...
The strangest thing about all I mentioned is that if I put the car on D or P it starts moving very slow with very low RPM. If I step on acceleration nothing's happening for about 5-10 seconds... then it starts accelerating and when it reaches ones 30km/h magically everything fixes and the engine, even still cold, starts working very smooth.

I know that for good troubleshooting it's good to read the error codes through the OBD. Here is my second problem I have tried to read the OBD with more than 10 different scanners, even two professional tools for Range Rovers and Mercedes and two scanners that are recommended in this thread: https://www.jaguarforums.com/forum/g...oved-**-33347/
Most of the scanners don't want to connect and the few that do establish connection are showing that there are no error codes recorded. And this is absolutely impossible, because last month I did a full transmission repair and since I have the car I have never cleaned codes.
So my question is - what could be the reason for this?! Could it be related to my problem with the not-working TRIP button on the left dashboard switch?!

 

Have you stripped down the top of the engine in any way recently? What work have you done apart from change the plugs? I'd suggest replacing any gaskets that could leak. For example the metal gasket sitting under the throttle body is a crush type, one use only.

Never use silicon sealant.

Have you any Check Engine lights? amber / red? Any messages?

Can you fill in your car's details in User CP so we know what year car we're talking about?

Have you got JTIS? Have you looked at the wiring loom diagrams? If not, why not? JTIS has been made super easy to download and install at the top of this forum.

OBD connections are something outside the scope of this forum, I've not seen this issue, although I've seen strange things happen when one is plugged in, like lots of errors scroll across the message centre, once unplugged these go away. Maybe google it for an answer, as the fix could be pan manufacturer, post back if you get it to link and post the codes...

How old is your battery?

 

First of all - thank you Sean for mentioning all this. I was planing to add information of my car in the forum's garage but never got time for it. Now I did it

To be clear - my car is 1998 XJ8 3.2 Sport and yes - I do have installed JTIS as well as the EPC and I did check the wiring diagram but I don't understand what it has to do with the unstable work of the engine?! If you are talking about the OBD I can't see the relation neither here, because the ELM327 bluetooth scanner is reading all data through such as RPM, MAF, speed, etc. but it shows no error codes - so the problem is not with the wiring.

About stripping the engine's top - no I haven't. I was planning to do it as soon as the temperatures around here goes a little bit up, but still haven't. One reason to do this is because when I was changing the spark plugs I noticed a small amount of oil residues over 3 of the old plugs and this is a clear sign that the gasket must be changed.
Apart the spark plugs I did: flush of coolant, oil and filter change, cleaning throttle, cleaning part-load breather, transmission repair, some suspension issues... Nothing related to the engine. And the gasket under the throttle body - I'll have a look at it and change it as well.

But, correct me if I'm wrong, I believe it's not a gasket as if it was - the engine would be unstable at any time, not just when it's completely cold + cold weather and only until it reaches curtain speed. It just sounds weird...

Check engine lights - not at all. Only "Stability control" message because of the old battery. But again - the problem is not related to this because when I was repairing the transmission I put a new battery for a while and the engine was working absolutely the same way!!! The only difference was with the spins the starter needed to run the engine, but the rough work was the same.
Beside this - no other messages on the dashboard! The last time i had a check engine light was before doing the transmission.

And for your last question - I did a good search around google and other forums... at this moment I haven't found any similar problem I still believe that the issue with the OBD is because of the scanners I'm using, not because of the car. I'm expecting soon to have access to Innova scanner and I hope it will connect properly.

But still - no clues about the unstable work of the engine And believe me - this morning the car was horrible... it was not only unstable but it tried to stall a few times by dropping the RPM under 400 while I was cleaning the ice from the front window. I had to enter the car and step on the acceleration to get back it's normal work.

 

It can be a flexible part that shrinks in the cold but expands and seals once warm.

You would end up with a temperature sensitive vacuum leak.

There is a rubber ring between the air pipe and the throttle body that sometimes does not sit quite right. The air pipe itself sometimes cracks in the corrugated section, often on the bottom side. Any air leakage past the MAF can be suspect but those two are easy to look at.

Then with respect to the OBD, there are some pins used for non-standard purposes on the connector. In addition, the protocol needs to be correct. There have been a few threads about this. Sometimes a wire gets dislodged from the connector at the trim panel.

 

I agree with you... and most likely it's some gasket on the engine - when I reach a certain speed the oil lubricates the entire engine-body (maybe) and that's why it normalize the work of the engine.

Nope - there are no cracks on the pipes - I know this for sure because after the breather problems I had a lot of oil residues even over the filter so I disconnected it and clean it well at home - I would notice if there was something wrong with it. And the rubber ring at the throttle is perfect as well - it fits very good so it's almost impossible for air to enter through there.

I just realized that in the past I've seen threads about some TCB connector which must be clean... or something like that! I don't know it well but as much as remember it could bring to such problems with rough work of engine. Can you at least tell me what was the correct word for this?


And back with the OBD - one of the standard things about this communication port is the ABS and Airbag status which is not related to any specific manufacture... and the scanners couldn't read even this! Well I suppose I'll have to dig a little bit in the forum and search again.

 

TPS, throttle position sensor

There are a couple of multiplugs on leads ending at the throttle body. The connectors can become contaminated or otherwise lose conductivity.

 

After following all the other threads in the XJ8 section and reading everything in this one: https://www.jaguarforums.com/forum/x...e-shake-67578/ I realized that it's about time to check my tensioners. It's been an year since I bough the cat and as the car is at 160'000 miles I was pretty sure that it's almost impossible for the original plastic tensioners to be still under the hood...

But now... with all this unstable work at cold weather + the strange sounds + engine shakes - I decided I should check.

Here is the important question. There is no way to find the valve cover gasket in Bulgaria - even the official Jaguar dealer doesn't have it stock So my only choice is to order the gaskets over Internet (maybe from ebay). Ok, but the delivery will take about a month and I'm afraid it's to risky to drive the car in this condition without knowing if the problem is coming from the tensioners... And it will be cheaper to order a full kit - tensioners + gasket.

QUESTION - I'm planing to open the valve covers and check the tensioners. If they are plastic or there is any kind of trouble I will leave the car in the garage and wait for the new tensioners and the gasket. But if the tensioners are the new metal model - how bad it would be to put back the valve covers with their old gasket and use the car for about 4 weeks until the new gaskets arrive!? What are the risks except losing some oil

 

To answer your question, you'll most probably have plastic tensioners. So the car will stay put! You will find out in under half an hour if getting the sockets out.

But, if not the implications of running the car until the new gaskets arrive are;
oil finding it's way into the plug holes and fouling the coils, this will give misfires and potential catalytic converter damage. It's a slim possibility.

Oil also leaks onto the exhaust manifold gaskets, so the smell of burning oil and smoke from under the bonnet. More likely.

Why so long to ship parts, 1 month is a long time? If you're planning in buying the parts from England maybe I could help?

 

While new gaskets might be preferable, some people routinely reuse them without problems. Anyways, it is far better than parking for a month, or driving without checking the tensioners.

New or used, a thin film of oil or grease on the mating surface helps to seat the gasket with less pressure.

 

For the first time since I'm reading this forum I'm glad to say - Sean, you were wrong The tensioners are just fine... Here are photos of what I found under the covers:




Something I was worry about is the dirt inside. It was looking very odd. Here is a photo before I cleaned it up:




Another strange thing was the "oil foam" I found in the breathers while disassembling. Here it is:



After closing the engine I decided to clean up the throttle body and it's connectors as well as change to rubber between the throttle and the plastic tube coming from the air filter.



BUT! The problem still remains - on cold start the engine is unstable... and it shakes! Why?!

 

Would it be problem for you to help me with the gaskets?! If you can give an address I can pay and order the gaskets to you and then you can ship them to here... Write me a private message about it!

 

Going back to your original post you say


The strangest thing about all I mentioned is that if I put the car on D or P it starts moving very slow with very low RPM. If I step on acceleration nothing's happening for about 5-10 seconds... then it starts accelerating and when it reaches ones 30km/h magically everything fixes


I assume you mean D or R (not P). That would make me suspect the throttle is not responding to the signal from the pedal. There was a recall for early XJ8 Throttle Bodies. Although the symptom was stalling at high speed, the issue was caused by the throttle body motor not reacting properly to the throttle pedal input.


It’s a long shot but it would be worth checking if your VIN was affected. Search for XJ8 Throttle Body Recall and you should easily find a list of the VINs. Your local dealer should be able to tell you if the work was carried out on your car.

 

That's right... my mistake. The problem appears when I switch to driving gear, including 4, 3, 2.

I have just checked about it. As my VIN is one of the first generations (836740) it's included in almost every list with issues So it's possible that my throttle body is affected and it might be not responding.

My car is originally from UK and the first owner took it from Merritts dealer (Jaguar UK - Lancaster Amersham) but I don't have any information about previous repairs.

What should I check about the throttle?! The only things I did on it is to clean it well as well as to clean it's connector.

 

Ideally you need to see if the butterfly is moving in direct response to pedal movement when you are having the problem, and if there is any difference when the problem clears.

You could perhaps see that from the TPS signal (backprobe connector) but the best option would be to monitor live data with a scanner when you get one connected (MAF, TPS etc).

Did these problems start immediately after your gearbox work? or is that just coincidental?

 

It's a good idea - I will do it as soon as the average temperatures increases over -20C around here I think that this weekend I'll have enough time to perform this check.

The best way to check the movement of the butterfly would be to remove the plastic tube and watch directly the throttle body, but unfortunately this will cause a huge problem because of the MAF and the amount of air that enters without being calculated by it. So I'll stick to a diagnostic tool to check the values of the throttle.

Nope... the problem with the unstable work was present from the first day I bought the car, it was there when I started the transmission repair and it's still an issue So there is not or at least doesn't seem to have any connection to that.

 

Ok, a little update over the subject with even more question back over the topic.
The throttle body is working properly or at least the butterfly is opening and responding to the acceleration pedal.
I gave the car to a friend who's very good mechanic and he told me to explain the following:
1. After a cold start (it's not related to outside temperatures but to a long period of time - longer than 2-3 hours) the engine is acting weird.
2. The symptoms - the engine is working as there is not enough fuel. When I step on acceleration a huge amount of air is entering the engine, but the amount of fuel is not enough and so the engine "chokes". This is the reason why the car doesn't want to run when and it's getting worst as I try to accelerate, but if I leave the car without touching the pedals it moves, but very slowly.
3. Ones the car reaches 2000 RPM it magically fixes... it doesn't demonstrate any kind of problem after that.
4. If I wait on parking until the temp gauge on the dashboard starts to move (maybe for 2-3 minutes) and then try to drive - the engine is working normally.
5. While working unstable - if I turn off the engine and start it again - it fixes the problem.
6. There are no errors - neither on the dashboard, neither trough OBDII.
7. Spark plugs are new NGK, the air-filter is clean, the part load breader is clean, throttle body is clean, as well as the throttle body connectors. The only known issue is the cam cover gaskets which I'm about to change.

We've tried almost everything to fix this unstable work... but nothing helps. The biggest problem is that we don't know what is causing this!

 

Just a shot in the dark here - maybe dirty injectors? You could try a can or two of injector cleaner. Cheap enough to try.

 

I don't think that this is the case... at least because the car is running on LPG as well and I've tried to run the car on LPG from a cold start and the engine was working absolutely the same. And the LPG system has it's own injectors...

So Other ideas?

 

Ok, I have a suspect - the MAF. But I'm not sure how I can check if the problem is coming from there. Maybe if I read live data through OBDII while starting the engine when it works unstable?! What values should I get if the MAF is working properly?!

 

Estilian - The 2-3 minutes when the temp gauge begins to move could correspond to the point where the system goes closed loop? You could check that through Live data. Having said that I still don't know why that would magically fix whatever is causing your problem.

I don't have any values for MAF but I could get some for you from my XJ8 3.2. I would not be able to do that until later this week so perhaps someone else may come up with some before that.