battery dying and strange idle speed

[Keesh]

ive noticed a few time that ill start the car and the base idle will sit at about 1000 rpm, normally mines about 600

after this happens, ill go to start the car and it cranks like the batteries flat and wont start, as soon as i hook up the jumper pack it starts strait away and i wont have any problem starting the car for the next 3 weeks,

then out of the blue i start the car and it revs at about 1100 again then i turn it off, go to restart it and its just drained.

my question is, why would the engine be revving so high if the batteries flat, and if the batteries not flat then why wont it start? ive swapped an alternator over but i didnt check the voltage reg.

on my digital dash it says its charging at about 13.5v with the lights on

anything at all???

[Keesh]

its a 8 month old acDelco maitnence free battery with 530cca

[VrWagz1]

fairly obvios one, but is your terminals tight and clean.
Im taking a huge stab in the dark, but possibly if the voltage is low it may play up with the voltage at sensors like the tps and cas, and cause it to give bad readings to the ecu and the ecu may open the iac more than it should?? maybe...

[Keesh]

brand new terminals, not bragging but my engine bay is clean as a whistle, i rebuilt the engine bay from scratch, brand new terminals all new alternator wiring, (i did this when i swapped the alternator, i was thinking if the batteries too flat the computer might keep resetting itself causing it to rev high

im just swapping the battery tomorrow with a 660 cold cranking amp battery
one of the benifits of working in parts is i dont have to fork out 130 bucks

[Dan355]

Sounds exactly like my problem mate but have stalling issues to. Let us know if the battery fixes it!