Engine idles high after battery replaced

[nicklisoire845]

Hi All,

I recently suffered a flat battery on my 98 xjr so I removed it to charge and hopefully breathe some life back into it again. This worked once but ill need to order a new one. Problem is when I reconnected the battery it fired but ran at a high idle (about 2000rpm) and also the ariel did not extend. I drove it for about 8 miles (or it drove me rather) I had to keep applying the brakes or use the J gate to avoid breaking the speed limit. I'm guessing that disconnecting (for 2 days in total) would have messed with the ecu? I have read on other forums it needs to go through a 'drive cycle' to recalibrate? I've also come across a suggestion that I need to remove the negative terminal and hold it to the positive terminal for 30 seconds to reset the system. Is there not a high risk of electric shock from this method? Any advice would be greatly appreciated. Thanks

[rosemary]

If you disconnect the battery terminals for a few minutes or disconnect the terminals and touch the negative and positive cables together it zeros out the ECU causing it to reset to original settings. If you contact Mike on J44EAG on the forum he can give further information on this.
At least it will eliminate the ECU as the cause.
Dave

[Andy P]

Hard Reset-Is there not a high risk of electric shock from this method?

Hi Nick,once you have disconnected the negative terminal you have effectively broken the circuit so no risk of electric shock.
Here's a bit more info to clarify:
You have to have a COMPLETE circuit for power to flow. If the negative(or pos) is unhooked from the battery you can touch the DISCONNECTED negative to the STILL CONNECTED(or visa/versa) Positive. There is not a complete circuit and no power flows. you can disconnect both if you feel more comfortable, but its not necessary, it just takes more time. The reason I and others say disc the negative is 2 reasons
1) it is usually the closest and easiest to access.
2) there is usually little or nothing else attached to it.
The reason it works on the capacitors is THEY still have a complete circuit on the car so you are giving their positive terminal a path to ground to discharge them. And since the ignition provides a mechanical link to circuits that are isolated. You can/should also switch the key to the on position while the battery is unhooked and hard reboot again. Then shut off the key and go back and reconnect the battery.....and no a hard reboot will not clear codes on ODBII. While it MIGHT, turn off a check engine light(depending on WHAT, the stored codes are) they DO NOT go away.

Just follow the instructions and good luck.
Are you able to scan for codes?If you can see if any come up.
Post back and let us know how you get on.
Take care.
Andy