WARNING: The following contains spoilers for Star Wars: Darth Vader #14, on sale now from Marvel.
Darth Vader is consistently making adjustments to his suit. As it is one of the main factors that keeps him alive and also grants him a much easier way of life, Vader ensures that his armor is always in perfect condition. When he is away from Coruscant and Palpatine for long periods of time, the Dark Lord of the Sith has often used scrap metal to keep his suit pieced together. It now appears that Vader not only maintained his suit but also improved upon it when necessary.
Vader has recently started his own hunt to reclaim the carbonite slab containing Han Solo. This led him to the Outer Rim where he formed an alliance with Bokku the Hutt in Star Wars: Darth Vader #13 by Greg Pak, Raffaele Ienco, Jason Keith and VC's Joe Caramagna. The pair followed a lead to a droid-run pirate repair center and data hub where Vader was ambushed by IG-88 and an armada of droids. Vader began to make quick work of IG-88 but was suddenly stopped when the assassin droid drew a datapad that stopped Vader in his tracks.
The datapad gave IG-88 full control over Vader's suit. This initially caught Vader by surprise but he was able to recover before IG-88 made Vader decapitate himself. Instead, Vader used the Force and summoned the datapad which he turned around on IG-88, forcing the droid to blow its head off. Vader was able to fend off the rest of the droids and a betrayal attempt by Bokku before focusing on the datapad.
He followed up on the datapad in Star Wars: Darth Vader #14 by Pak, Ienco, Keith, and Caramagna. Vader tracked another assassin droid connected to IG-88 and followed it to Coruscant where it met with Sly Moore and a council of betrayers. The council scattered and Vader pursued Moore into a building where she trapped the Sith. She then tried to use another datapad that she designed to perform exactly the same as the datapad possessed by IG-88. Unfortunately for Moore, Vader was not taking any chances. He had fixed the fault in his armor after his encounter with IG-88, making her attack useless. He then made Moore submit to his will before using her to serve a separate purpose.
Throughout Greg Pak's Darth Vader run, Vader has made considerable repairs to his suit. The series opened with Vader's failure at turning Luke to the dark side in Empire Strikes Back. This caused Vader to disobey Palpatine and instead follow his own path. This did not work for Palpatine who felt that Vader's actions were a clear sign of betrayal. Palpatine used his Force lightning on Vader, greatly damaging his suit before bringing his apprentice to Mustafar and leaving him for dead.
Vader was able to pull himself up and find shelter within a former Trade Federation base. He then built himself back together with spare parts. This included finding pieces that could act as an arm and a leg as Vader had lost one of each during Palpatine's punishment. Vader was able to fend off assassination attempts from Ochi and Sly Moore while wearing his poorly repaired armor. Vader's suit would not return to peak condition until he was back in Palpatine's good graces.
While Vader would often have to repair his suit on his own, he rarely ever made any improvements to his suit. Possibly the greatest improvement he ever made came in James Luceno's novel Dark Lord: The Rise of Darth Vader. Palpatine had informed Vader that he was aware that the suit was vulnerable to electrical attacks, notably his Force lightning. This led Vader to outfit his armor with electrical insulation.
Darth Vader knows how essential his suit is to his survival, thus he takes whatever means necessary to ensure that it functions properly. While this more often than not means that Vader was simply repairing his suit, he also added improvements to strengthen himself. It's ironic that Vader's most protective improvements were developed as a result of threats within the Empire. Without Palpatine's consistent betrayal, there's no telling if Vader would have survived as long as he did.