Ok well I had this problem last summer when my car was stock when it got warm it would idle really low and just jump back and forth when I would sit at a light or whatever, but it would never stall. Now after i rebuilt everything and with the vortec heads and LT4 hotcam its doing the same thing. I haven't got a new chip burned for it yet. So my ? is the chip causing this or soemthnig else b/c its doing the same thing when the car was stock. I replaced all the vacum lines when we did the rebuild. Any idea's anyone?

 

May be a vacum leak, causing the idle surge up and down.

 

I had a bad surging idle problem similar to what you described and In my case, it was a couple of bad fuel injectors. I had my injectors rebuilt before assembling the motor so I didn't even think to check them, so it took me awhile to locate the problem

If you have access to a multimeter It is easy to check the Ohms of the injectors and it's something you can eliminate as the cause. Also make sure the check the injectors when the car is warmed up, because on my car the Ohms values change a lot when hot.

 

Thats what i was told it could have been last summer but now I have all new injectors so I don't think its the injectors.

 

i gotta go with the vacum leak as well.

i just had this problem and it was a vacum leak. wasn't much fun to find it, but it cured the problem.

good luck!!

 

I kinda have a stupid question. I work on cars a lot, but I am stupid when it comes to electronics. How do you use the multimeter correctly to test the injectors. I think I have the same problem and I already checked for vacuum leaks and the idle air control and a bunch of other stuff.

 

Anyone? I would like to test these things out

 

the only tests you can run on injectors with a dvom is an ohm check, you set the meter to read resistance & then measure across the terminals where the harness plugs into. also, you use it to see if the injectors are shorted from both terminals to the
body of the injector. this should be done with them both hot & cold.

the next 2 parts are dangerous,... NO smoking, NO sparks, NO fires, or any other sources of ignition of any kind.
to check them for leaks, you have to pull them out & pressure them up.
also needed is an injector trigger, even though i use mine once or twice a week i forget the actual name of it, but it hooks to the battery & to the injector. most have 3 setting on them, you can use it to see if an injector will click when triggered, & also when the injector is pressured up to check the spray pattern, pressure drop & volume. after checking the volume & pattern you then check them for leaks again.
2 other tests that can be done requires a scope, which is not cheap. the cheapest single channel scope is i think around 500.00.

 

you can also test for leaky injectors by

1. hooking up a fuel pressure guage
2. blocking off the return line from the fuel rail
3. turning on the ignition

if your fuel pressure goes up and holds your injectors should are ok. if the pressure goes up and then drops off quickly you have leaky injector.

this test will not work with a holly AFPR, it will 'leak' down on it's own. holley said they designed it that way to releave pressure from the system.