I have a 1999 Grand Caravan and it has recently been suddenly accelerating for about 15 seconds then going back to normal. Even when in park, it will suddenly increase rpms for 15 seconds then back to normal idle speed. What might be the problem?
you have a problem with either the aic or you have a vacuum leak.sure the air idle control vale might be bad,but if it was your check engine light would have come on.but you dont state it did which im sure you would have mentioned it.so i would look for a vacuum leak.also if its low on oil it will idle in a similar way so check it.
That may be called a "hunting" or "rolling" idle and be caused by a lean air/ fuel mixture. A test can be done as described below after disabling the Idle Air Control (IAC) computer controlled idle. Also clean your throttle plate and IAC valve.