Skip the auto shop - Our mechanics make house calls

Q: Misfires at idle

asked by on

I have a relatively new truck that's idling rough. If I'm sitting still, it stays at around 500 rpms, but every few seconds the needle dips and goes back up. I've been to the dealership several times, but they keep telling me it's normal. I have another chevy truck that doesn't do this. One line they're feeding me is that the engine deliberately misfires one cylinder while it's idling to do some sort of diagnostic check every few seconds. Is that true? If not, what else can you suggest as a cuprit?

A: Hello. This engine does do a series of self...

Hello. This engine does do a series of self-tests, but you should not feel them. Since the idle is so low, I typically check the throttle body as it may be defective since the vehicle is still so new. If that is fine then I would typically start by reprogramming the vehicle's computer. If the problem is very subtle, then it is normal. If it is very well-pronounced, then you need to get GM's service center involved if the dealer is not helping you with this, as your car should still be under warranty. Alternatively, a technician from YourMechanic can diagnose your engine's misfire and determine exactly what needs to be repaired for you.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 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!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Power steering.

Hey there, thank you for asking about your 2003 Chevrolet Suburban 1500. You may have a pump that has stuck vanes inside it. You can try and let it run a while until it gets the fluid hot and vanes...

Q: Replace small engine

The Del Sol's in 93 came with either the 1.5l or the 1.6l engine. Converting over another Honda engine can be done, but will require quite a bit of modification as the engine wiring harness and ECU would need to...

Q: Truck misfires when the engine warms up - 1995 Chevrolet C3500

If the heat sensitivity is a good clue, this could well be the ignition control module, which is quite heat sensitive on the big block Chevy's. Would check fuel pressure (while running) as well to make sure you're getting enough...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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...