A Glitch, also known as a Bug, is an error in the game that produces an effect that was unintended by programmers and appears in almost every game.
The Glitches often arise from mistakes or errors in the game's coding which go unnoticed during development and testing of the game. Glitches can be unintentional and may cause problems to the player, but some glitches may be used to the player's advantage.
Some glitches are prominent than others and each one are specified and/or shared on a certain console (where these depends of the console's technical aspects). One of the most popular and common glitches is nicknamed "Blue Hell", which is featured in every game since GTA III. Once the player enters Blue Hell, they will fall for 5–10 seconds before returning to the surface.
Walking Above The Porter Tunnel
One method of reaching Staunton Island and Shoreside Vale when they are inaccessible, without cheats, is by exploiting a glitch that allows the player to walk above the Porter Tunnel. To do this, one must drive a car to the concrete sea wall above the tunnel entrance on Portland Island. The player has to park the car right along the edge of the wall, in line with the tunnel. When the player exits the vehicle, they will fall through the sea and into Blue Hell, but will land on top of the tunnel. The player can then walk along the tunnel, then jump into Blue Hell at the Staunton Island or Shoreside Vale end, so that the player can get teleported above the surface.
Walking Above The Subway Tunnel
This glitch can be performed at the subway in Shoreside Vale at the airport. When the train arrives to the platform, take the very last door of the train. Enter the train and then get out again. Claude will teleport above the platform and will be standing above Blue Hell, and the player will be able to see the tunnel. The player can run on top of the tunnel (they have to jump over one of the first holders for the electricity cables in the ceiling, otherwise they will fall into the tunnel). If the player gets arrested or killed, they will respawn on the last island they unlocked. If the player wants to get to Shoreside Vale, they can jump into Blue Hell and will respawn on the ground of the island.
Rhino Spawn Glitch
Taxi Driver Glitch
The player can transport people in any car besides the Taxi or Cabbie by executing the following glitch. Enter a taxi cab, and press and hold the side mission button. Keep holding the button and exit the cab. Then enter the car to whichever one the player desires (except for other vehicles with side missions). Once in the new car, release the sub-mission button and the Taxi mission will start. This glitch has been fixed on the iOS port of the game, however.
Easy Vigilante Glitch
Whenever the player is performing a Vigilante mission, get close to the target car and pause the game before entering the menu screen. Once gameplay resumes, the criminal in the car will stop and proceed his/her "getaway" on foot, being much easier to kill. Also, he will most likely engage in shooting other pedestrians if the player is not his nearest target. If this does not work the first time, just try again and/or get a bit closer.
"Killer Look" Glitch
When on foot, if there is anybody trapped under a car and the player uses the first person view, they will die instantly. The death will not be added to Claude's tally. This also happens if the pedestrian is trapped under the car and the player starts a mission. This glitch has been fixed on the iOS version of the game however.
Pedestrian Money Glitch
Quite rarely if a pedestrian is killed, they may drop a large sum of cash, usually a total of at least $3,000. This may be a glitch in the programming from the money drop rate, as this glitch occurs to almost any pedestrian.
Inside the narrow tunnel that runs beneath St. Marks (which links Portland Docks with the Harwood Train Yard), there are four pedestrians that spawn, supposedly remnants of Darkel's gang, a deleted character. Drive a Bobcat into the tunnel and stop within view of the gang. Get out of the Bobcat, jump on its hood, and walk up to its roof. The four pedestrians will start walking around aimlessly. When the player walks back down onto its hood, four more gang pedestrians will spawn in the same spots. The pedestrians will respawn whenever the player repeats this action, though the game will freeze after at least 40 peds have spawned. If the player kills them, they will drop Molotov Cocktails. This glitch has been fixed in the IOS version however as walking up and down the bobcat now merely respawns the existing pedestrians, rather than spawn extra ones.
Accessible Joey's Garage Glitch
The player can access Joey's Garage and see the whole interior as seen in cutscenes, by driving a car into the left garage door. Run on the left corner between the door and the garage. After a few seconds, the player will be inside the garage. This glitch doesn't seem to occur in the PC version of the game.
If the player starts a new game on a memory card with Rumble completed, the Purple Nines will not spawn in the new game as they permanently disappear after that mission. This will make it impossible to complete Uzi Money and subsequent D-Ice missions, as killing randomly spawned Nines is the sole objective of these missions.
Import/Export Crane glitch
If the player dies whilst a vehicle is being transferred to the boat from the crane, the crane may be frozen in the position it was when the player died, rendering it unusable. You will no longer be able to get 100% completion, since the Import/Export side missions are required for completion.
Vehicle Spawn Glitches
The 10th Anniversary iOS port of GTA III is notable for containing many car spawn glitches and other abnormalities. Occasionally, moving vehicles have the tendency to spawn floating in mid-air due to a spawn glitch. After a few seconds, they will quickly fall back to the ground and continue driving. Also, cars may sometimes spawn abnormally inside the Porter Tunnel, where they will appear stuck inside the walls of the tunnel or submerged inside the road.
Garage Closing Sound Glitch
If the player manages to park three vehicles in a two-vehicle garage, the sound that the garage door makes will play rapidly and the garage door will not close. This can be achieved easily with the oversized garage of the Staunton Island Safehouse, by driving one car into the garage, parking another car halfway inside the garage and halfway outside of it to prevent the garage door from closing, driving a third vehicle into the garage, then driving the second vehicle into the garage.
Car Resurrection Glitch
If a car explodes inside of a garage, walking away from the garage to close the garage door then walking towards the garage to open it will reveal that the car has respawned in its original state. This is due to the limitations of the game's engine. When the garage door is closed with a vehicle inside of it, the vehicle will despawn, and a fresh copy of the vehicle respawns when it is opened. The game doesn't record the state of the vehicles when they are driven into the garage (e.g. damage, damaged parts, etc.), just the vehicle model and color.