" and then now i swapped the coils back to the originals that were in the car and it runs well.
so it seems to me the MAF was the problem. amongst likely other things "

I always had a low confidence level that the coil connectors are on fully

Vee had a suggestion of putting a slight twist on the MAF connector pins / blades for better electrical pin contact which these untouched pins may be on the edge giving you your changed MAF observation

 

Since i've got another car for my increased commuting the Jag was under the cover all the winter just being started, warmed up every week or two and then covered back. Was lucky to get the UK market ECU for rather rare for them naturally aspirated 1997 4.0 XJ6. Since it's emission C, i was thinking i will get rid from EGR and pre-cat oxygen sensors. So today was the Jaguar Day.
And results are
1) ECU is 1997 so to connect to it with IDS it needs a 97 VIN last six
2) Original car had an immo so mine didn't start on it. ECU brought 1621 and 1622 codes.
3) I've got two 95 VDP ECU's and looking inside i couldn't find any differences among all three ECU's except some lettering so worth a try to swap the EEPROMS. (UK has 9733 chips and said it was updated to 1410CC, mine both have 9761 as both have T493 recall done and updated to 1410AL).
4) After swap car started right away (EGR valve, EGR temp and pre-cat oxygen sensors were disconnected) with no CEL, warmed up and allowed to recalibrate the TPS and oxygen sensors. Although it still needs to use a 97 VIN to connect too so it's in the EEPROM not the ECU mainboard.

And finally being hot it idles nice and without the shudders i've got before so probably it was an EGR thing as i thought. Thinking now to replace the intake to non-EGR as i see them a lot for sale on UK ebay.

PS. Biggest issue is elder daughter will be 16 next year and she has seriously put an eye on this car...

 

XJREngineer would probably be the best reference on the ECU interiors as the exteriors and hardware should be the same just operating software