I recently replaced the battery in my ‘99 Toyota Corolla, and ever since I did that I’ve noticed that after starting the car from cold its idle speed is low (the vehicle has no rev counter, but the engine idles just above stall speed). The idle condition improves slightly once the engine reaches operating temperature, but still appears rough. The replacement battery is a 628 specification and the previous battery was a 631. I have cleaned the throttle valve and apart from this issue the vehicle runs fine. Please could you advise?
MAHIN CHAUHAN
Bulawayo
Answer: There should be no correlation between the battery change and the altered idle characteristic. Although the new battery is slightly larger in size and capacity, that should not impact on idle speed (its best to fit the correct battery according to the owner’s manual). The only links we can think of are:
• Modern ECUs learn certain values (such as injector offsets) that can be lost during a battery change and it has to re-learn these values over time. We doubt that that is the case with a 1999 model-year Corolla, however. You can try and disconnect the battery again for at least 30 minutes and connect it again to see if the situation improves as it “learns” new values, but we doubt that it will make a difference;
• There may be an alternator problem (why did the previous battery fail?) that results in maximum resistance on the V-belt as it tries to charge at full capacity for some reason, which will impact on the idle condition. It might be worthwhile to have the charging system looked at by an electrician (you can obviously measure the voltage over the battery terminals yourself – it should be around 12V before starting, and around 14 V with the engine running.
If the measures above do not resolve the issue you are back to square one and will have to look for air leaks in the intake system, inspect the condition of the idle-control valve, as well as the throttle valve. When last was the vehicle serviced? If not recently, then it would be a good start to eliminate dirty air filters and old spark plugs.
