A 45-year-old MTA mechanic tried to kill himself and his 2-year-old daughter with pesticides and chemicals found in fire extinguishers because of a bad relationship with his estranged wife, authorities said.

Both were in critical condition after the bizarre incident.

The unidentified Queens man, who has not been charged, mixed ammonium chloride into his daughter’s baby bottle and also sprayed her with insecticide inside his car on Monday morning, police said.

He parked behind a strip mall in Lawrence, LI, near the Queens border, and at the last minute beeped his horn at another driver and asked for help, sources said.