id change the coolant temp sensor
Mine did this and I found out it was the timing belt that needed to be changed.
if you got an automatic depending on what gear it is you may need a 2800 or 3500 rpm stall in your torque converter call a transmission shop if that's it they will help you
it has a pass 2 key antitheft system.most likely cause would be the key lock in steering coulm
If a car idles fine but stalls when put in gear, it may indicate issues with the fuel system, such as a clogged fuel filter or failing fuel pump, which prevent adequate fuel supply under load. Alternatively, it could be related to a problem with the ignition system, like worn spark plugs or ignition coils that can't handle the increased demand. Additionally, vacuum leaks or a malfunctioning idle air control valve could disrupt airflow and engine performance when engaging the transmission. Diagnosing the exact cause would require further investigation.
choke has to be set exactly right fine tuned
EGR Valve ans sensor went out at the same time. Replaced them and it's good to go.
check your fuel pump, it may be working fine, but have a loose valve in it. also check your fuel tank, an old trick to play on people is to drop lots of plastic tape in their tank, it stays forever & sucks down onto the fuel line, temporarily blocking it, the vehicle stalls, then after it sits, starts again.
The most common reason for a vehicle to run rough when it is cold is bad spark plugs or bad spark plug wires. Change the spark plugs and spark plug wires.
Possibly a defective torque converter lock-up solenoid. Disconnect the solenoid and see if that cures the problem. If so replace the solenoid.
If the boat idles fine and revs fine in neutral in the water and idles fine on the trailer, however has no power when you stick it into drive and give it some throttle a common problem with some of these early Mercury V6's is in the stator. The only way to fix this is to replace the stator.
== ==
Probably a bad idle air control valve.