Q: Vehicle's engine stops turning over when at speed.

asked by on

At first, the truck was losing power and the engine stopped turning over only when idling. The truck would start back up after sitting for a second and then the engine would stop turning over anytime it idled. I did a full tune -up and for about a week the truck had no issues. Today, while at speed on the highway the engine stopped turning over twice and started back up after a few minutes. The third time, It sounded like it was trying to turn over but didn't and had to be towed. Please assist.

My car has 420000 miles.
My car has an automatic transmission.

Hi There, It sounds like you may have one of two possible issues. The issue of idling and stalling may be related to a dirty or faulty idle air control valve. The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This valve is controlled by the vehicle’s computer and will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about ~800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve.

When the truck stalls at highway speed and does not immediately start right away after, this suggests you may have an ignition coil that may be starting to fail. Ignition coils are coated with a varnish-like insulation that becomes brittle over time after being stretched then contracted repeatedly The insulation develops small fractures that open when heated and close when cooled. When open, they allow shorting of coil windings and decrease or eliminate the coil’s ability to function. This type of temperature cycling happens because every time you shut the engine off, the fan stops running, the coolant stops flowing and the temperature under the hood rises. Every time you start the engine again the coolant flows, the fans turn on, and the temperature drops. When this heat dissipates and is absorbed under the hood, it is trapped causing this cycling effect. Components that contain heat sensitive materials include parts like coils, injectors, igniters, and some sensors. Any of these may be potentially subject to this same kind of heat problem which can be very difficult to trace. I would recommend having an expert from YourMechanic come to your location to take a look at your vehicle.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. Vehicle's engine stops turning over when at speed.

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: My car is idling rough and flooding out when first starting. What could be causing this?

This may be related to a dirty or failing idle air control valve. The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at...

Q: hi my chevy malibu goes in reverse,neutral,park but not drive

If no power train codes appear, other than the misfiring on cylinder no. 2 which is not relevant to your issue, there may be a mechanical or hydraulic failure in the transmission such as a failed piston in a clutch...

Q: Oil cap is milky, but the dipstick isn't and the coolant isn't bubbling. Please advise.

The discoloration likely represents the effects of entrained moisture in the oil on the cap surface. There can normally be a certain amount of condensation in an engine, for example as weather conditions change or if the engine sits for...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.