Q: Bad gas mileage, rough idling, rear end noise

asked by on

I've been getting very bad gas mileage on my car. It used to be in the 18-24 MPG range, depending on whether I drive it on a highway or in the city traffic. It's now dropped to 10-13 MPG. Also, my car started idling roughly a bit. Besides this, the rear end of the car, on it's right side, makes a thumping noise. I figured that something must be loose so I went to the shop and they had the shocks checked. They are fine. Are these problems connected? What should I do?

Hi there, thank you for writing in about your 1997 Jaguar XJ6. The poor mileage and a rough idle is potentially due to a bad coolant temperature sensor or a broken wire to this sensor (the coolant temp sensor that is connected to the fuel injection). A broken wire in this circuit sends a false "cold" signal to the engine causing excess fuel consumption.

If the thumping noise you mention occurs while driving, you may have a failing constant velocity (CV) joint on the right side axle. If you would like to have this looked at, a certified technician from YourMechanic can come to your car’s location to diagnose the rough idling issue, thumping noise, and decreased mileage in order to have this properly corrected.

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. Bad gas mileage, rough idling, rear end noise

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: Q: Low gas mileage

Hello. The fuel mileage rating on most vehicles is a rating estimate of the fuel mileage you should get. The problem with this rating you see in the windshield is based on city or highway driving. Both of these ratings...

Q: Q: My '98 expedition drives fine for a while, then after a few hours, when sitting still, it idles rough then shuts off.

After some testing done to verify the EGR valve flow to see if the valve is intermittently sticking open causing the stall. This can be done using a scanner with the capability to open and close the EGR valve and...

Q: TRUNK FUSE BOX

The trunk has two fuse panels one on left rear and one on right rear of trunk area. The one on the right has the fuel pump relay and fuse. The trunk door lock is in series with all the...

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...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
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.