A new battery will make a big difference to help the car start after being left for a while or in cold or damp weather, best to get a high spec / heavy duty one and check if it needs to be a silver calcium one

who serviced it/ what was done (in detail)/ when did you start having the trouble with your engine?

the EGR valve can be a source of trouble, you don't need it, get rid of it by fitting a blanking plate, solid (no holes to let gasses through) stainless steel 3+mm, available online for about £5 - car will run much better/ will still pass an MOT/ you should have no problems due to the plate

the inlet manifold will need cleaned too - but with the EGR blanked, it may have a chance to un-gunk its elf

you may have faulty glow plug/s - this is cheap to replace - some other potential problems are not (eg - injectors)

you can aquire a code reader online for about £20 that can read your fault codes, - good investment / may save you money the other thing is do you have a hanes manual? - another good investment