My jaguar is having idling problem after initial starting and when I slow down . the engine felt like misfire in the spark plugs is it a common problem with s type? how can I fix it?

Automatic transmission ??
Check engine lamp illuminated ??
Cold engine idle speed ??
Warm engine idle speed ??
IAC (Idle air control) system operation ??

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I'm guessing you have over 100000 miles , definitely replace all the spark plugs and ignition cables and cap and rotor if your motor is such equipped. If you want a better idea of which cylinders are misfiring, go to your local Checker or Autozone and ask them for code retrieval, codes stored will give you an idea of what is failing. Code po300 is multiple misfire, po301 is cyl #1, po302 is cyl #2 and so forth.

you felt it or the OBD2 told you?
or both, ?
this a engine swap? 2000 Acura TL Mini?

misfires hot, or cold engine, or both,
in gear or not,idling, slow, fast or hills only, or all time?

You need to know if it IS misfiring. Does it shake at idle?
Typically I recommend experienced techs deal with misfires.
the code should say P030x, with the X being the number of the cylinder it believes is misfiring (No, computers arent always right about which cylinder. USUALLY, but not always.)
Lets assume it says CYLINDER 3. (Only your scanner will tell you for sure, 3 is an example we are using for now). You could try disconnecting cylinder 3 ignition coil plug at idle. On a good cylinder that is NOT misfiring, you will hear and feel the engine run rougher and slow down when you unplug its coil or injector. Thats because it WAS contributing until you unplugged it. Your v6 engine idles at say 600rpm warm when its running good. If you unplug any 1 cylinder, youve lost 1/6 of the engine output (actually more due to dead weight drag from that cylinder, but not important for now). SO, if you find the cylinder it says is misfiring, and it loses rpm when unplugged, its probably doing SOMETHING or trying to. If you unplug it and zero change heard or felt, that cylinder is likely dead.

Heres where it gets hard. Could be literally dozens of things that take some familiarity and experience to ID. bad spark, bad fuel mix, bad spark plug, oil fouling, low compression, leaky valves, blown headgasket, leaking intake, EGR leaking at idle, wrong weight of motor oil (some cars) and the list goes on. An experienced drivability tech can usually narrow it down or find it in 1 hour or less. If you are learning as you go, you could take many hours, and still miss things that trained eyes and ears wont.

Start by figuring out which cylinder. If it idles smooth (No shake at idle, and if you clear code and start it and let it idle the light never comes back till you drive over 75 as you stated), then I strongly recommend a professional check it.
If it idles rough and you know which cylinder, you can try taking out that coil and spark plug if you know how, moving them to another cylinder that isnt misfiring, then clear the code and drive it and see if the same code resets or a new code for the other cylinder sets. If the code is the same, you have deeper issues not worth explaining here.
If the code moves to the new cylinder, then 1 or both of the 2 parts you changed are likely at fault. You can replace them an very likely fix the issue.
Again, I strongly recommend professional help. But that may get you started.

What code (check engine light on ) ? Misfire ? P0300 , random misfire ? What engine does it have ? 3.3 or 3.8 . By hiccup you mean a misfire ?

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

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Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

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Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

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Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

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This will help.

Thanks.

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

-----------
Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

-----------
While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

------------
Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

--------------
Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

-----------
Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

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And for .......

Car not starting or turning over indicates towards multiple possibilities. It can be issue with battery or weak battery. But if battery checks out ok, then it can be starter issue or faulty alternator or problem with low fuel pressure or no spark at spark plugs due to dirty spark plugs or faulty ignition coil or injectors getting cracked or dirty and needs to be cleaned.

To confirm the problem, the basic troubleshooting is required.

Click this link below and follow the troubleshooting:------

http://technoanswers.blogspot.in/2012/02/car-starting-issues.html

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This will help.

Thanks.

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

-----------
Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

-----------
While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

------------
Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

--------------
Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

-----------
Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

----------

This will help.

Thanks.

Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example).

When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.

What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad spark plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.

"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.

Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.

Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose, so let's start with a steady misfire in one cylinder before moving on to intermittent misfires.

Hope this help.

Have the Idle Contorl Solenoid checked.