6

I tried to start my car today but something strange keeps on happening. It turns on just fine, but once the engine is operating it starts revving to 4000 RPM even though I am not pressing the gas pedal.

I tried turning it on and off again and also tried a "hard" reset by disconnecting the battery for a few mins and then re-connecting it and trying again... but alas the engine still revs to 4000 RPM for no reason.

At the time of typing this question, its currently summer here in the UK, so I know its not doing this to make the engine warm as the weather isn't cold.

What could the issue be and how can I fix it myself?

My car is a 2005 Jaguar S-Type 4.2 V8 SE.

Thanks, Dan.

  • 2
    I'm betting your Jag is Drive-By-Wire (DBW), meaning, there isn't a direct connection between you and the throttle. If so, the gas pedal rheostat is probably telling the computer you are pressing it, causing the throttle to go up. You could possibly test the gas pedal by unplugging it and checking for even/smooth operation by putting an ohmmeter on the leads. You may also try tromping on it a couple of times with the engine off. If you want to send reset the CPU, you need to let it sit for ~30 mins to ensure the residual power is gone. This is the first thing I would have tried as well. – Pᴀᴜʟsᴛᴇʀ2 Jul 9 '15 at 22:21
  • 1
    @Paulster2 I think it could be. I'm pretty sure most cars are these days, because all/or most of the have engine management systems now. I will try the CPU reset and see how it goes. Thanks! – hello_world_daniel Jul 10 '15 at 9:57
  • Looking for what parts are on your car, I found your car is DBW. This is the likely place I'd look for an issue, as this single part tells the computer what speed to run the engine at. It takes the driver input. If it's seemingly telling the computer you want to have the engine run at 4k, the computer will oblige, especially since it's not beyond the redline. It's at least a plausible working theory to run with, lol. – Pᴀᴜʟsᴛᴇʀ2 Jul 10 '15 at 11:10
  • @Paulster2 Thanks for your help. In the end it turned out there were two faults. A CPU reset and a replacement gas pedal rheostat fixed the issue. Thanks! If you put this as an answer, I would be happy to tick it :) – hello_world_daniel Jul 13 '15 at 7:26
4

I'm betting your Jag is Drive-By-Wire (DBW), meaning, there isn't a direct connection between you and the throttle. If so, the gas pedal rheostat is probably telling the computer you are pressing it, causing the throttle to go up. You could possibly test the gas pedal by unplugging it and checking for even/smooth operation by putting an ohmmeter on the leads. You may also try tromping on it a couple of times with the engine off. If you want to send reset the CPU, you need to let it sit for ~30 mins to ensure the residual power is gone. This is the first thing I would have tried as well.

Looking for what parts are on your car, I found your car is DBW. This is the likely place I'd look for an issue, as this single part tells the computer what speed to run the engine at. It takes the driver input. If it's seemingly telling the computer you want to have the engine run at 4k, the computer will oblige, especially since it's not beyond the redline.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.