Surging / Hunting at idle

[Serviceman24]

Ok, so i just re-installed my BBSC after having the bearings replaced in the drive shaft. The car hasnt been started in quite some time and I had to replace the battery. Once all of this was completed and I started the car, it surges and hunts at idle. I let the car warm up completely and it stayed the same. It fluctuates between 500 to 1100 RPM and almost sounds like it wants to stall. If you give it gas, it seems to be fine and then drops back down and continues to surge.

Any ideas as to whats going on and how i can fix this?

Thanks in advance!

-Wade

 

[Briank]

Sounds like a vacuum leak.

 

[SexyRed]

vacuum leak.

 

[Serviceman24]

So where do start to find out where the leak is coming from? Is this common?

 

[tnguyen]

check all your vacuums, when the car is running, spray carb cleaner on the vacuum hose and see if the idle changes, if it does at a certain spot on a hose, replace that hose.

 

[TXvsLV]

also could be the throttle body adjustment if you've taken it off or moved it in any way

 

[htmachine]

I have the same issue. Was working on the DS power window and with the door gasket partly removed couldn't close the door. I had turned off the dome light but forgot about the foot well lighting. Battery died so charged it and now have the idle hunting issue. I didn't even open the engine cover. The dead battery is our common denominator. Does the ECU have to "learn" something? I'll let you know if I find something.

 

[TomCat]

My (nearly) same symptoms (after CTSC install) turned out to be an unplugged EACV (which is hard to see as the plug is on the bottom of the air control valve).

 

[Old Guy]

I think that the only thing a dead battery would do is wipe out stored error codes. May or may not wipe out trim settings - I can't remember whether those are in flash or SRAM. Did you charge the battery with it still connected in the car. If you have a good charger that should not present a problem; but, if you had one of those rapid charge things I don't know how high the charge voltage gets, could present a problem; but, unlikely.

I don't have my service manual handy so I can't check to see if fuel trim is reset on a power loss. If it is and your car was running close to the limits on fuel trim before the battery was killed, the loss of trim may result in the engine running lean and suffering from some lean surge. 'If' it is trim, driving the car will gradually restore the trim settings and make the problem go away. If it does fix it self, I would be inclined to investigate why the car was running with so much trim.Personally, I think this is a lower probability possibility. If you have an early non DBW car, I would definitely be giving TomCat's suggestion a check and have a look at the EACV to make sure that it is operating correctly.

As an observation, I disconnect my battery every fall and reconnect it every spring and the car starts and runs perfect. Loss of power to the ECU does not normally result in operating problems. Something else is in play.