Dear Jaguar adepts
Our SType had a bit of a problem.
When started cold and put in reverse, it runs rough, the engine light comes on and goes in limp mode.
30 seconds later, once we start driving, the engine runs smooth as it schould.
It is a 2003 2.5 petrol S-type.
At that moment, just after starting the cold engine, the vacuum of the brake assistance hardly works either.
If somebody has an idea…much appreciated!

Tia!
Alain

 

Welcome to the forum.

My first thought is the power brake booster has a vacuum leak. The booster has a check valve to retain vacuum after the engine is shut off. The booster can typically hold vacuum for several days of inactivity.

If the check valve or booster itself is leaking, the engine would run quite lean when first started, to replenish the vacuum reservoir inside the booster. This might explain the initial rough running which then goes away.

To test this theory, disconnect and plug the large vacuum line to the booster. Do NOT drive like this, as considerable pedal force will be required to stop. Start the engine and see if it behaves now. If so, you’ve got a leaking brake booster or check valve.

 

Similar scenario with one of my s types is occurring. Cold starts are rough and brake pedal is weak until engine warms up. Will test further using this method. Thx

 

Another method to test the brake booster: This one is easy to do but requires an overnight wait.

Go for a drive and make sure the brake pedal feels normal (power assist working). For best results , do this in the evening, or some other time when you can shut it off and leave alone for 12 hours or more. After shutting off the engine, do not touch the brake pedal.

The next day, get in the car but do NOT start the engine yet. Press on the brake pedal and the power assist should feel normal. Typically you can apply the brakes 2 or 3 times before you feel resistance increase. The general idea is if the engine were to stall while driving, you’d still have normal power assist to safely stop.

A brake booster and check valve in good working order should also hold vacuum overnight. If the pedal feels hard right away, the system has a leak and is not holding vacuum.

Is a possible vacuum leak also the root cause of the rough running? Don’t know, but if leaking you’ll want to get that fixed regardless.

 

Thank you for the replies! I will give it a try and write the results here.
best regards
alain

 

I was thinking on the idle control valve on the air intake butterfly and a good cleaning of the whole part but I am not even sure there is an ICV on this engine.
To be checked

 

Meanwhile, I changed spark plugs and coils and the throttle body. All vacuumleaks are repaired also
problem still happens but I noticed that it only happens when it rains…misfire on 2/4/6
Read about possible water that infiltrates via the plastic part underneath the wipers.
gonna remove that part and give it a good clean to be dure that the drains are not blocked
the saga continous…

 

Yes and here is the TSB showing where the water leak is. It's not a drain it's a hole that let's water onto the top of the engine. So you just want to plug the water pathway. It was covered by some tape from the factory and that can get damaged over time.
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Dear clubairth1

thank you very much for your reply and possible cure!
I hope this solves our problem.
This would have been very difficult to diagnose.
The force of a forum proven!
thanks again,
best regards from Belgium
alain

 

Your most welcome and I hope it does fix your leak. But it is simple and cheap once you get pointed in the right direction to look. So something to at least check.
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Dear clubairth1

Today I had the time to do the necessary stuff of the Jaguar maintenance note that you gave me.
I also found that the drainpipe of the screenwiper, left side, was loose so water leaked on two connectors underneath.
I have no idea what these two connectors are. One has a rectangle piece with two wires attached, like an old capacitor? do you?
I hope this solves our issue…
many Thanks for your advice! Will keep you up to date.
best regards
alain

 

Exactly this scenario, exactly the same symptom and pattern, occurred some years ago on my wife’s 2.5 X-Type. The problem was easily solved and it was none that has been mentioned. My memory of this is that it was a leaking intake gasket (WELL, NOT QUITE: see below). My dealer solved it quite simply by replacing the gaskets (SEE BELOW)…but in fact it was a posting on the X-Type list about these symptoms and the fix that enabled me to suggest the problem to the dealer. This was years ago and it has never happened again (and we are now in year 20 of daily use of this car).

Records checked: Scan (on my BlueDriver OBD reader) showed misfires on cylinders 5 (P0305, cylinder 5), (P0301, cylinder 1), (P0300, Random/Multiple cylinder misfire detected) and (P0303, cylinder 3 misfire). Car taken to my dealer. There the problem was diagnosed as "Signs of oil/vacuum leak at the variable intake units". The solution: "Installed variable intake solenoid o-rings". 2 of them, part number C2S40669005 .
Solved. This was in January 2019 - cold ambient temperatures. And the symptom on starting the engine cold: rough running, and engine warning light on. Once the engine warmed up all symptoms disappeared...until the next cold start.