Grand Theft Auto IV Cheats

Manhunt 15G: Complete the most wanted side missions from the police computer.
Cleaned the Mean Streets 20G: Capture 20 criminals through the police computer.
Fed The Fish 5G: Complete the mission "Uncle Vlad".
It'll Cost Ya 5G: Complete a taxi ride without skipping from one island to another.
Sightseer 5G: Fly on all helicopter tours of Liberty City.
Warm Coffee 5G: Successfully date a girl to be invited into her house.
That's How We Roll! 10G: Unlock the special ability of helicopter.
Half Million 55G: Reach a balance of $500,000.
Impossible Trinity 10G: Complete mission "Museum Piece".
Full Exploration 20G: Unlock all the islands.
You Got The Message 20G: Deliver all 30 cars ordered through text message.
Dare Devil 30G: Complete 100% of the unique stunt jumps.
Assassin's Greed 20G: Complete all 9 assassin missions.
Endangered Species 50G: Collect every hidden package in the game.
Under the Radar 40G: Fly underneath the main bridges in the game that cross water with a helicopter.
Dial B For Bomb 10G: Unlock the special ability of phoning for a bomb to be placed.
Gracefully Taken 10G: Complete mission "I'll Take Her".
Liberty City (5) 20G: After meeting all possible friends, the ones left alive all like you above 90%.
No More Strangers 5G: Meet all random characters.
That Special Someone 10G: Complete mission "That Special Someone".
You Won! 60G: Complete the final mission.
Liberty City Minute 30G: Complete the story missions in less than 30 hours.
Key To The City 100G: Achieve 100% in "Game progress" statistic.
Teamplayer 10G: Kill 5 players who are not in your team, in any ranked multiplayer team game.
Cut Your Teeth 5G: Earn a personal rank promotion in multiplayer.
Join The Midnight Club 10G: Win a ranked multiplayer race without damaging your vehicle too much and with damaged enabled.
Fly The Co-op 15G: Beat our time in ranked versions of "Deal Breaker", "Hangman's NOOSE" and "Bomb da Base II".
Take It For The Team 10G: Be on the winning team in all ranked multiplayer team games.
Top Of The Food Chain 10G: Kill 20 players with a pistol in a ranked multiplayer deathmatch.
Top The Midnight Club 20G: Come first in 20 different ranked standard multiplayer races.
Wanted 20G: Achieve the highest personal rank in multiplayer.
Auf Wiedersehen Petrovic 30G: Win all ranked multiplayer variations, all races and "Cops 'n Crooks", as both sides.
Let Sleeping Rockstars Lie 10G: Kill a Rockstar developer in a ranked multiplayer match.

Easter Egg: The Heart of Liberty City
First, you'll have to have access to Happiness Island. Once you're able to go there legally, find the Helicopter Tours (which is directly east of Happiness Island) and steal a helicopter. Fly to Happiness Island and over the Statue of Liberty, then jump out of the helicopter at the statue's feet. You should land on the topmost tier of the statue, which is basically a square platform with a door in the center of each side. Run around the platform until you see a door with a plaque on either side of it that reads, "No Hidden Content Here." It may seem like you cannot go through the door, but you can-- it doesn't open, you simply walk THROUGH the door. Inside, you'll find an empty room with a tall ladder. Climb it, and when you reach the top, look up; there is a gigantic beating heart, held in place by chains.

Easy money
Go to an ATM, then cause a traffic jam to the area. Wait for someone to take money from the ATM, then kill him or her. Make sure to block any nearby roads so the ambulance cannot get to the murdered victim. Take the money they dropped on the ground. Then, run a short distance away, and go back. The money should have respawned on the ground. You can repeat this as many times as desired. You can also kill more people taking their money from the ATM to increase the amount of money that respawns.

Repairing the engine
If the vehicle you are driving breaks down and the engine will not start, call 911, and your engine should start again.

Friendship Bonuses
By gaining friendship with the following people can benefit you in many ways.

Boom? (Call Packie for him to make you a car bomb): Gain 75% friendship with Packie
Chopper Ride (He will pick you up in his helicopter): Gain 70% Friendship with Brucie
Discount Guns (Buy weapons at a cheaper price from Lil Jacob): Gain 60% friendship with Little Jacob
Extra Help (A car of gang members will be sent to help you out): Gain 60% friendship with Dwayne
Free Ride (Call for a taxi): Gain 60% friendship with Roman

Unlockables
Annihilator Helicopter: Kill all 200 Flying Rats
Rastah Color Huntley SUV: Complete 10 Package Delivery missions
Remove Ammo Limit: Get 100% completion

Get a Statue of Liberty T-shirt
Go to the statue of liberty and walk up to the second level. Walk through the door (it doesn't swing open, just go through it) and the game will load for a second and you will walk out with a new t-shit with the statue of liberty on it.

Friendship Bonuses
By gaining friendship with the following people can benefit you in many ways:

50% off for all Clothing Stores: Get 80% Relationship Status with Alex
Boom? (Call Packie for him to make you a car bomb): Gain 75% friendship with Packie
Chopper Ride (He will pick you up in his helicopter): Gain 70% Friendship with Brucie
Discount Guns (Buy weapons at a cheaper price from Lil Jacob): Gain 60% friendship with Little Jacob
Extra Help (A car of gang members will be sent to help you out): Gain 60% friendship with Dwayne
Free Ride (Call for a taxi): Gain 60% friendship with Roman
Health Boost (Call Carmen and select "Health Boost"): Get 80% Relationship Status with Carmen
Remove Up to 3 Wanted Stars (Call Kiki and select "Remove Wanted"): Get 80% Relationship Status with Kiki

Rastah Color Huntley SUV
To Unlock Rastah Color Huntley SUV you have to successfully complete 10 package delivery mission.

Wheelie Rider Achievement
Grab a motor bike and approach Francis International airport then go to the one end of runway, now accelerate your bike and do a wheelie, to do this you have to press left analog stick down for 500 feet to get this achievement. Runway is ideal here because here you have a very long and clean path where you can drive without any trouble.

Rolled Over Achievement
Get a fast car and go to the runway e.g Super GT, Infernus etc. Find a yellow ramp scattered along the runway grass then hit one of the ramp with high speed in a way that only half of your car hits the ramp, this will give you enough spins to get the achievement.

At Algonquin Bridge which connects Dukes to Algonquin locate the part where the lanes split at the bridhge when going towards westbound. There is a small ramp at the split, hit that ramp at very high speed and it shall roll over your car several times and if you land in the lower area you will get more spins.

Walk Free Achievement
Go to the airport runway in a car, get out of car and you will instantly score a four star wanted level which you require to get the achievement. Now drive or run to the end of runway and you will get the achievement.

Find cops and if you kill them your wanted level will rise. When you have scored 4 star wanted level get into the vehicle and drive into subway tunnel. As soon as you leave the flashing wanted circle and your wanted level disappears you will score the achievement.

Join The Midnight Club Achievement
To get the achievement keep joining and quitting games/matches until you become the host. Then setup the lap no to 1 and start a new helicopter race with few opponents.

Jizz Reference
There is a detergent inside the laundromat which is being used and displayed above the back washing machine is Jizz! Big Washing Power, its an obvious attempt at cruel humor.

Chain Reaction Achievement
To get this achievement, make a traffic jam in the enclosed area e.g booth tunnel, you can do this by blocking off both lanes with two automobiles. When cars back up, steal some of them and squeeze them in between others so that there are 3 or 4 next to each other then throw a grenade at automobiles in front and use the RPG to destroy the others.

Spider Man Reference
Occasionally pedestrians passing by you will say "Look it's your friendly neighbour.. oh, no never mind"

Brown Note Reference
Around Faustin's house there is a reference to a great legendary musical note. When you are in that area go to dead end about a block away towards the water. Now hop over the fence which is on your left while you are facing the water, there should be a man sitting on a beach reading a book with title "The Brown Note". Musician's joke that this is a note that when played causes bowel movements by the person playing it.

Completion
All of the following tasks must be completed to achieve a 100% completion rating.

Activities - Defeat the CPU or an in-game friend at all activities at least once.
Car Thefts - Deliver all 30 vehicles to the garage.
Flying Rats - Find and kill all 200 pigeons.
Missions - Complete all 90 main story and procedural missions.
Most Wanted - Kill all 30 pedestrians on the list.
Random Characters - Find all 14 random characters and complete their encounter missions (except Jeff, Cherise, Clarence, and Ivan).
Unique Stunt Jumps - Complete all 50 jumps.
Vigilante - Complete 20 crimes.

Two bits!
Get any type of car and go to a large traffic jam. Use the horn to do the "Shave and a haircut" and stop, one of the many other cars should do the "two bits". You must listen carefully because it might be done by a pedestrian instead!

Easter Egg: Fire Truck Madness
If you boost a fire truck, press the fire button while driving around. This will allow you to shoot the super-powerful water cannon at anyone around you. Watching people react to getting shot with high-speed water is hilarious.

Easter Egg: Prank Calls
Here's something funny to try. During your adventure through Liberty City, you may find phone numbers written in inconspicuous places, such as on the side of a building or in the subway. If you dial these numbers, you'll usually get someone on the other end who you can subsequently prank.

Mr. tasty + GTA Theme Cheat
When inside a Mr. Tasty Ice Cream truck, one of the the songs the truck plays is called the GTA Theme, in a cycle order it is usually played after Flight of the Bumblebee. While playing the song, call ZiT, and a text message will confirm telling you the name of the song. As soon as the message is answered, a Cheat Activated confirmation will appear, and the cheat will appear in the Cheat section in your phone. Cheat gives you full healith and Body Armor.