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: I was at 50 miles from empty. I just filled up to full and it only gave me about 215 miles from empty. Typically it holds up 350 p

The fuel range calculator in your car's computer works based upon your most recent driving conditions. The throttle position sensor constantly calculates your fuel range based upon your driving behaviors. You will notice, if you are driving more aggressively or...

Q: Idling while driving

The main issue you have here is the number of miles on your car. With this many miles, most cars would have been completely worn out. Unless you have taken meticulous car of your car, it is often necessary to...

Q: Squeaking noise, battery loses power. 1996 Jaguar XJ6

Hi there, thank for writing in about your 1997 Jaguar XJ6. It sounds like the alternator drive belt (accessory belt) is loose, glazed, or worn out, and should be replaced. A second possibility is that the belt tensioner has lost...

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...
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...
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.