Q: When stopped waiting at a stop light, the engine RPMs will drop a bit and it sometimes stalls out.

asked by on November 21, 2016

2008 Jeep Patriot 4x4:

From time to time, usually when stopped waiting at a stop light, the engine RPMs will drop a bit (from about 600/500 to 300) and sometimes even stall out. Most of the time its not a big issue, as the car will give a slight jolt back and forth and then go on as normal. I would say this happens maybe once every other week. Most of the time happens when sitting and idling at a stoplight. Do you know what is causing this?

I bought the car used with about 85,000 miles on it. Not sure about the maintenance history. Would replacing the spark plugs help with this? The car is only worth a few thousand dollars, so I don't want to put a ton of money into it.

Thanks for your help.

My car has 91300 miles.
My car has an automatic transmission.

Idle Control Valve Replacement $147.54 - $995.01 Get a Quote

This is a common sign of 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 idle. This valve is controlled by the vehicle’s computer which will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed. This is all controlled by the idle air control valve. When the engine RPM drops below the normal range of 750-800 RPM (for most cars), this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your idle air control valve.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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


Experienced Mechanic?

Earn up to $70/hr

What others are asking

oxygen sensor

Hi Destiny. Thanks for the follow-up question. A V6 engine has (4) total O2 sensors, Bank One sensor 1, Bank 2 sensor 1, Bank One sensor 2, Bank 2 sensor 2. Bank 1 and Bank 2 refer to different sides...

Shifter slides into neutral w/o using button on shifter and while driving

This is normal way the shifter works. The button would need to be used to get from neutral to reverse. There is nothing wrong with your vehicle's shifter.

2003 Chrysler pt cruiser's steering wheel is extremely hard to turn. Checked fluid and it was good. What should i do?

Possibilities include low pump output, a poorly drive pump due to a faulty drive belt, a binding rack and pinion unit, restrictions in the pressure lines, and binding in the steering linkages. The only way to diagnose the pump is...

RPM fluctuation every few seconds with AC on at Idle in my 2013 Ford

Hi there. It is common to see a small fluctuation in RPM when the AC turns off and on due to the drag on the engine. It should not drop that much though. It sounds like the idle control system...

My truck cranks but it won't start - 1994 Chevrolet C2500

Hi. A couple of things to check: When the engine is at top dead center, does the rotor under the distributor cap point to the number 1 cylinder? It is very important that the engine is at top dead center...

AC off - 2011 Chevrolet Cruze

Hello. Your Chevy Cruze uses a "heated" engine thermostat (under computer control) which has caused some problems. There is a Technical Service Bulletin (301268) to address the "engine is cold" issue - software reprogramming). There are also multiple temperature sensors,...

AC squeaking

Your vehicle only uses a single serpentine belt. So, if you're only hearing the noise when the A/C is turned on and not all the time, the belt and tensioner are not to blame. My guess is that the noise...

Related articles

How to Buy a Good Quality Idler Pulley
The The idler pulley system drives a car’s alternator and is part of a belt and pulley system that also covers power steering, the air compressor, and other devices. The pulley is essential; with all of the important equipment that...
Symptoms of a Bad or Failing Exhaust Gas Recirculation (EGR) Tube
Common signs include rough idle, rattling noises from the engine, and the Check Engine Light coming on.
How Long Can I Leave the AC on While My Engine Is Not Running?
You’ve parked your car, and are sitting inside waiting. Maybe you’re early for work and don’t want to head into...