Q: The car engine runs erratically when it is cold, then runs just fine after the car warms up after a while.

asked by on

Been trying to figure out the cause for this. Spark plugs, fuel filters, o2 sensors...replaced quite a few parts but the problem persists. In the morning after the car has cooled overnight, it runs rough. It sputters, chokes, hesitates, the RPM dances up and down when I accelerate.. it's just not smooth. After a few miles of this the car finally warms up to what I guess is operating temperature and the ride smooths out completely. The problem dissapears. Until the car cools down again. Any idea what it might be that's dependent on the engine temperature? It hasn't done this before at all; surely it being an old car has to be a factor. Thanks!

My car has 171000 miles.
My car has an automatic transmission.

Try checking the coolant temperature sensor. When the engine is cold, the enrichment function relies heavily on the coolant temperature sensor to determine how much fuel to supply at lower temperatures. If this is not working properly, it may struggle to settle into a well running pattern. For example, if it is 30 degrees outside and the temperature sensor reads 100 degrees, this may send false information to the ECU causing it to send false information to the fuel injection system. A qualified professional from YourMechanic can inspect the rough running problem and verify the needed repairs.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. The car engine runs erratically when it is cold, then runs just fine after the car warms up after a while.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Protection mode is blamed for engine shutting down

Hello there, thank you for asking about your 1991 Buick Reatta. What the previous owner is saying could be correct. Resistor sensing contacts are located in the ignition key lock cylinder of your vehicle. When the key is inserted, these...

Q: Slight jerk when changing gears, especially when starting from a complete rest.

This may be a sign of a failing mass air flow sensor or a throttle position sensor. The mass air flow sensor is a unit in the intake system that monitors air intake as it is mixed with fuel prior...

Q: Sporadic RPM surging while stopped in the traffic

Fault codes should be read out of the ECM on your 2006 Mercury Montego. All connectors on the engine harness and at the ECU need to be checked for condensation and/or water ingress as these will cause drivability problems. I...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.