How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Matt Your Own Question
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22897
Experience:  BEng hons Mech engineering, in auto industry 22 years
Type Your Car Question Here...
Matt is online now

When i start my car at any point in a journey it revs up to

This answer was rated:

When i start my car at any point in a journey it revs up to 1800 and settles down about 3 minutes later... after a*****on the motorway my car randomly stops accelerating so i have to quickly pull over to the hard sholder before i loose all speed. mecanics have done computer tests and nothing has come up...they said it could be my battery as it was only running at 30% and could be that the vaults arent getting to the throttle control properally????
If you could help please??

a faulty battery can produce this fault
but if it resurfaces then this could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;
Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

- Also replace the spark plugs if any of them fail this checklist:
Matt and other Car Specialists are ready to help you