Hello, I have a bit of a problem and was hoping someone can point me the direction of a more likely cause.
WHen in Drive at a stop light, RPM randomly starts fluctuating up and down 50 to 150 RPM. Using diagnostics, at these moments Alternator Load [%] is jumping between 25-60, however MAF sensor is also doing 4 to 4.8g/s or so.
During winter the car worked perfectly, had fixed all the vakuum leaks, etc. The battery is new , having around 4 months. Load test of it shows 12.5V and 640A out of 720A. Its hard to say, but about a month after replacing battery not only these fluctuations started happening, I am also getting P2503 Charging System fault with CEL+Red Battery Light (very randomly, having 12.5V in early morning and sometimes it does illuminate immediately after start up, sometimes half a minute after, sometimes when started driving, and sometimes it doesnt even show up.
THrottle [%] doesnt fluctuate, therefore Throttle Body isnt the problem?
Alternator has new voltage regulator and bearings, charges as supposed. When battery lights up red , alternator was giving 14.2V at that moment.
Can anyone of you point me in direction what to go for next? Maybe fix up alternators wiring with a potenciometer to turn off smart charging? Or get a new MAF (I tried cleaning this one up)?

 

Mantas, I could get my hands on a can of carb cleaner and remove the intake pipe off of your throttle body. Using the carb cleaner, spray the throttle body (open and shut) to remove all brown residue. Make sure to focus on the edge of the silver disc (the butterfly). May need to use a rag and some of the spray to remove that. Put the intake back together and attempt to start the car. If it doesn't want to start, return the key to the OFF position, put the gas pedal down as far as it will go and then start the car. Putting the gas pedal all the way down turns off the fuel injectors and pushes only air through the motor to clear the flooding. After say 5 seconds of cranking, start easing up on the gas pedal and bring the car to idle. See what your idle is like now. IT should fix the bouncing that you are seeing. Now, because of the steady idle, you may see your charging issues go away too.

 

Thermo, you are a life saver, helped me many times! So thank you very much for everything!
I cleaned up throttle body during winter, following your advices to others. Well, I redid it today as well. Unplugging MAF sensor (or actually forgetting to plug it back in) actually fixed the idle for a single drive home, so will have to be tested further more.
About the battery light, it seems verry intermittent. Today 4 times out of 5 immediately on startup light came up, and after ride home it was showing only 12.5V on idle, but after restart ir goes to 13.9ish.
I checked single positive wire alternator-starter-battery, resistances , everything is fine. However tho, I found your answer for someone else about checking wiring on alternator, and 4pin connector blue wire is only 8V (you mentioned if its lower than battery voltage, light will show up) , the wire from fuse box has a good voltage like battery, but the wire from GEM is around 3V (I see you mentioned if it is less than 11V , problem is wire or GEM). I work on heavy trucks, so I dont have diagrams and its tough to find for Jaguar, so if it is not a big bother could you provide me some additional guidance..
I checked continuity red-green striped wire from alternator to massive connector close to Coolant expansion tank, only 2 of the same color there are , 1 is different, and the other one seems to be it , or isnt it? I would run a new wire from there to alternator , but I am not sure if that wire is actually supposed to be the one? Maybe you could throw in a pic of wiring diagram so I can make a decision, if GEM is faulty I am thinking of wiring potenciometer to control alternator , thus removing smart charge system. Shorting blue-wire to positive would remove the battery light..
​​​​​Well, something to keep me up late. Hope I am not being too much of a bother, but thank you!

 

Mantas, if you don't have diagrams, PM me your e-mail address and I will send you a set. Then we can go from there. Based on what you are describing, you either have a connector that is loose or has some corrosion on it. Lets get you the diagrams and then we can be talking "on the same page". (You had to see that one coming, LMAO).

 

Love it , Thermo. Lol!
i PM'd you, having diagrams life will be much easier! Thank you!