I changed the plugs on my vibe today and had some freaky things happen. I started by taking off the battery negative post as suggested by chilton manual then proceeded with changing the plugs with much effort. I am convinced now these were the original plugs or they have not been changed in a long long time as everything below the plastic cover was a fight to get apart(138K Miles bought it last month). After finishing and hooking up the battery cable I started the vibe and it was idling at about 500 rpm and the engine was shaking more than usual after running a few minutes the idle improved to about 750 rpm so I took it for a 10 mile drive and came home and then the idle was back up to what I have been used to as warm idle or even a little better to my great relief and everything seems fine now. I did have to reprogram the door lock mode to number 2 the way I like it. Does anyone know why this happened, it is like the car had to learn how to run right with the new plugs. The new plugs were NGK Iridium IX Part 5464 and were a recommed part for my 1.8L vin code 8 1ZZFE and I checked the gap and put anti seize on the plug threads at installation. Tomorrow I am going to change the PCV valve since I think it also is the original just for the sake of peace of mind I sure hope nothing freaky happens again(knock on wood).
The ECM learns as you drive, to improve it's driveability. When the battery is disconnected for a time, it loses all it's learned and has to take time to relearn a new set of data. Give it some time.
What hogdoctor said is correct. To add: manuals will always tell you to take the battery cable off for safety reasons, actually for liability reasons. Every time you go under the hood you have that opportunity to jolt yourself. However if your battery plus is covered up that possibility becomes a remote one. Under the car you have another jolting opportunity at the starter.
I rarely take the battery cable off in order to avoid this relearning period. When working on the front fascia I do take the cable off because I do not want the airbags to deploy accidentally.
Vibrologist
'05 Vibe
"It is important to know the difference between 'accurate' and 'precise' even if you are neither!"