Hello! I have a slight problem and need some advice.. For past 4 months I have been running my 2.5 V6 petrol X-Type with new Spark plugs , but their gap size was 0.7mm. When really cold weather began, on cold starts at -20celcius RPM was going really low and sometimes engine shutting off, so I had to keep pressing gas pedal (holding it still wasnt helping , had to manually be pressing ir many times to keep RPM) for around 30seconds , then engine would run really well. So I googled and found out my Spark Plug gap had to be around 1.3mm. Today I removed them and regapped for 1.3mm instead of 0.7mm. Now the engine isnt running right, RPM @idle is going 650 to 1000, engine sounds a little rough. Feels rough driving as well..
My question is, can it be that regapping was a bad idea and I just need to get a new set of spark plugs (what kind should I order) ?

 

Spark plug gap = x type
JTIS gap specification is 0.051" to 0.057".

0.12954 mm To 0.14478 mm

 

Double platinum plugs shouldn’t be re-gapped from factory. There are several threads about the cold start problems and many things to check and or replace to solve it. Crank sensor, coolant temperature sensor, vacuum leaks are the most usual suspects in fixing the cold start problems. Spark plugs won’t cause the cold start problem. The plugs will cause misfires at any and all temperature ranges. But since you re-gapped them then chances are their going to need to be replaced and when you do go with the Bosch fine wire double platinum or an alike grade plug and don’t gap them

 

Thank you for your reply! I have an update of the situation: so basically I have Iridium spark plugs factory set at 0.7mm. Everything was running really good, but had rough cold starts at very cold mornings. I regapped to 1.3mm them and immediatelly engine was idling rough at 650-1000 rpm. Drove fine. Today I regapped them again to 1.0mm and engine isnt even driving well, works rough, etc. Doesnt seem to have any leaks.
So I need to get double platinum plugs factory gapped at 1.3mm and thats it ? Or should I keep in mind something else? Thank you again

 

Mantas, the plugs should be gapped to 1.3mm as per the service manual for the car.

As for your random idle, I want you to get a can of either carb cleaner or throttlebody cleaner. Remove the intake from the car (where it bolts to the throttlebody) and then using the can, wash away anything that is brown. You should be left with an all silver inside. Do not forget to use your finger to open the butterfly valve (the silver disc blocking the air flow) and clean that to (especially the edges which may require a rag with a bit of the clean sprayed on it). Lets see what you have at that point.

Now, of note, when cleaning the throttlebody, odds are, you are going to flood out the car. This is easy to overcome. Get into the car and hold the gas pedal to the floor (as far as it will go) and then attempt to start the car. DO NOT WORRY!!!! Having the gas pedal on the floor as you start the car is a signal to the computer to not admit fuel. So, the car is only going to crank over, not actually start. After a few seconds of cranking, you can then start letting off the gas pedal, feathering it as needed to bring the car to idle. I have seen the rough idle a few times before and this seems to clear it up.

 

Thank you for your reply! The thing is , before I started messing with spark plugs , idle was perfect. Less than a month ago I have cleaned throttle body, Evap valve, intake manifold, MAF and other valves/sensors that go to Intake manifold.
I definately will try flooring the gas pedal and crank it over. Thank you!

 

you say poor idle after changing spark plugs on a 2.5.
Assuming you replaced the ring seals on the intake check for other vacuum leaks. spray brake cleaner around to area to check if its hard to get at and listen for engine change on idle. Don't assume new spark plugs are all good. I have been caught out with this once or twice.
Look for air pipes with hidden splits I have not worked on a Jaguar yet but many other cars. Check anything which would have been moved. Not sure on the injectors and connections but some cars these can be very fragile and they break off under the plug. Seek simple things first.

best of luck sure others will know more than me.

 

Mantas, following another thread and thinking back to the history if the X-Type, it may be that you have a style of plug that the X-Type just doesn't like. These motors seem to be really picky to what plug you put into them. I know there are a few posts about recommended plugs and which ones to not gets as they are perpetual problem makers (anything with a "multi-spark" label this motor hates). So, it may be that you put in something that the car simply hates. I know it sounds silly, but if you do a search for issues with spark plugs, you will find a ton of them with people having similar symptoms to what you are having.