trigger feels sticky and sometimes the drill keeps running after i let go.

Diagnosis

The sticky trigger and "run-on" effect in the Milwaukee M18 FUEL 2904-20 are typically caused by the accumulation of fine particulate matter—specifically drywall dust, sawdust, or concrete slurry—inside the trigger housing. This debris migrates past the external seals and coats the mechanical return spring and the electronic potentiometer. When these particles mix with moisture or factory grease, they create a viscous sludge that prevents the trigger from snapping back to the neutral "off" position instantly. Because the 2904-20 utilizes a variable-speed electronic trigger, the "run-on" occurs when the debris physically wedges the trigger in a slightly depressed state, or when conductive dust creates a bridge across the switch contacts, trickling current to the motor controller even after you have released your grip. You can confirm this by checking if the trigger has a "spongy" feel or if there is a visible gap between the trigger face and the tool housing when the drill is idling.

How to Fix It

To resolve this without a full teardown, you must chemically displace the contaminants. Follow these steps precisely:

1. Remove the M18 battery pack immediately to kill all power to the logic board.
2. Use a high-pressure canister of compressed air or a blow-gun attachment on a compressor. Direct the airflow into the gaps between the trigger assembly and the main plastic chassis, focusing on the top and bottom of the trigger pivot point.
3. Apply a non-residue electronic contact cleaner (such as CRC QD Electronic Cleaner). Use the thin red straw nozzle to spray directly into the trigger housing gaps.
4. While the cleaner is still wet, rapidly cycle the trigger from fully depressed to fully released 20 to 30 times. This mechanical action breaks up the sludge and allows the solvent to flush the debris out of the housing.
5. Rotate the tool and repeat the spraying and cycling process from the opposite side of the trigger assembly.
6. Wait approximately 10 to 15 minutes for the solvent to evaporate completely. Do not reinsert the battery until the tool is bone dry to avoid shorting the electronic speed controller.

If That Didn't Work

• Full Switch Replacement: If the internal return spring has snapped or lost tension, cleaning will not work. You will need to replace the entire trigger switch assembly. This requires removing the 10-12 Torx screws holding the clamshell housing together. Be careful not to lose the small plastic alignment pins when separating the halves.
• Potentiometer Calibration: If the drill runs at a very low speed even when the trigger is released, the internal potentiometer may be skewed. Try "exercising" the trigger by pulling it firmly to the full stop several times; if the issue persists, the electronic module is likely failing and requires a professional board replacement.
• Housing Obstruction: Check the exterior plastic housing for any melted plastic or deep gouges from a drop. Sometimes the trigger isn't sticky internally, but the outer shell has deformed, creating a physical pinch point that prevents the trigger from returning. Use a fine-grit sandpaper to smooth any burrs on the interior of the trigger slot.
• Battery Terminal Cleaning: In rare cases, "ghost" running can be caused by carbon buildup on the battery terminals causing an erratic current flow. Clean the battery contacts and the tool terminals with a cotton swab dipped in 90% isopropyl alcohol.

Heads Up

• Avoid Lubricants: Never use WD-40, silicone spray, or graphite powder inside the trigger. These attract more dust and will turn into a thick paste, permanently seizing the switch.
• Dust Management: If you frequently work in drywall or masonry, use a vacuum to blow out the trigger area every few hours of use to prevent buildup.
• Battery Safety: Always remove the battery before performing any maintenance. The M18 FUEL series has sensitive electronic controllers that can be fried by a single stray drop of conductive cleaner if the circuit is live.
• Overheating Warning: If the trigger feels "mushy" after heavy use, it may be the thermal protection circuit engaging. Let the tool cool down for 10 minutes before attempting a mechanical fix.