New battery install = issues

[CopperRouGe]

So...I've got an automatic 2006 Mazda3 hatch 2.3L with 135,000kms

I installed a new Interstate battery and something went wrong. Started the car and had a CEL. Pulled the code and it was U0100. Reset the car by pulling the cable off the battery and the CEL went away.

But the issue now is that my idle is very low and irregular. It bounces from 500-800 rpms and the car surges when crawling in traffic.

Any info would be a great help, thx.

[midnightfxgt]

Are the terminals tight?

That code is: "Lost Communication With ECM/PCM "A"

Sounds like the terminals may be loose, and with the idle of the car, may not have a solid connection. Did anything other than a dead battery prompt you for a new one?

-John

[Flagrum_3]

I would suggest the same, check that your connections are good, but also clear the code and drive the car for awhile; like 1/2 hour or more, to let the computer learn again....This may clear the erratic idle.

_3

[CopperRouGe]

I just replaced the battery because it was the original and it was starting to crank slow. Didn't want to get stuck somewhere.

I'll double check the terminals and see what happens. I've driven the car to work today, 50 kms, and the idle is still off.

To reset the computer, pull the - or + off battery?

[Noisy Crow]

Always remove the -ve. If you put a wrench on the +ve and it hits a metal part when you are loosening the bolt you'll end up with a dead short... sparks everywhere, and not good for the battery.

[CopperRouGe]

Done. Will try and do that at lunch time and see what happens.

[mazdabetty]

But the issue now is that my idle is very low and irregular. It bounces from 500-800 rpms and the car surges when crawling in traffic.

This is actually normal after a reset, or in your case a replacement. How many kms have you driven so far? We did a reset on mine recently and it bounced around quite a bit like you explained when slowing down. Stalled it about 50 times (it's an automatic hahha).

Finally after about 60kms when it didn't go away we did some research and ended up cleaning out the throttle body. Worked great. Let the car idle for about 10-15 minutes and drove it around for about 30 minutes to let the car relearn its old habits. Did some bouncing around for the first few kms but seems to be good now.

It's worth a shot if the above suggestions don't help :)

[CopperRouGe]

I've driven the car for around 50 kms so far. I'll pull the neg cable off and see what happens and if it continues, then more work will have to done.

Thx for all the replies

[morganc]

Ditto. I had the same symptoms. Cleaned the body, starts great and idles awesome.


This is actually normal after a reset, or in your case a replacement. How many kms have you driven so far? We did a reset on mine recently and it bounced around quite a bit like you explained when slowing down. Stalled it about 50 times (it's an automatic hahha).

Finally after about 60kms when it didn't go away we did some research and ended up cleaning out the throttle body. Worked great. Let the car idle for about 10-15 minutes and drove it around for about 30 minutes to let the car relearn its old habits. Did some bouncing around for the first few kms but seems to be good now.

It's worth a shot if the above suggestions don't help :)

[CopperRouGe]

Update: The car seems fine now. I just drove it and let the computer do it's thing.

I will probably clean the tb out when it's warmer out. It won't hurt.