RamAir LS1

Here is my situation. My car is (was) basically stock until last weekend. Stock tune, stock throttle body, stock injectors, stock MAF, stock bottom end, stock top end, and it is an M6 car if that's relevant. I have a lid and a catback, no headers (yet). I got a BBK SSI intake and replaced my LS1 intake with it. I kept egr. The swap took me a while but it is now completed. The car starts up and idles fine while its cold (open loop). As soon as it gets to about 160 degrees (and switches to closed loop) the car starts to surge while it is idling. It will rev smoothly above 2000 rpms. As soon as the throttle is released it starts surging again. At first, from about 800 to 1000 rpms. After about 60 seconds it will be surging between 500 and 1500 rpms. If it is shut off for a few minutes and started back up it will run smootly for about 60 or so seconds, the switch back to closed loop and start surging. It has me stumped.

Here's some stuff i've ruled:
-vacuum leaks (i sprayed carb and choke cleaner behind the manifold and all over the other vacuum connections. I also sprayed it between the manifold heads and the idle didn't change so i feel confident the intake gaskets seated well.)
-map sensor is plugged in
-cam position sensor is pluged in
-pcv does not have any broken lines and is all hooked up
-egr valve is relatively new
-no ses codes
-IAT is plugged in
-intake air valve is plugged in but i am going to replace it just to be able to rule it out
-MAF is plugged in
-all injectors are plugged into the corresponding plugs
-the two big plugs by the valve covers are plugged in
-throttle position is plugged in


I've gone over it all like 5 times and have been dwelling on it for like 2 days. I keep coming back to the idle air valve and am planning to replace it just to make sure. Please chime in with ideas.

On a side note I did drive it and it definitely increased the power significantly.

jim ravencraft

Hi,
i had a similar issue with intake change.check bump stop/iac voltage/tps voltage. The hole in throttle body - mods will create idle issues. Pull a vacuum check.. See if readings are normal or indicate issues. If all is well a tune should do the trick.......... have a blessed day! Jim

edcmat-l1

iTrader: (10)

Data log. Without it, you're just guessing.

RamAir LS1

I changed the idle air valve and it did not fix the problem. I did a lot of research around the web, a post on this section of LS1tech that I stumbled upon helped fix the idle.

https://ls1tech.com/forums/pcm-diagn...e-relearn.html

Great stuff. Thanks to all.

gofastwclass

iTrader: (2)

I agree. Some of the best car related money I ever spent was on tuning / scanning / logging software.

01ssreda4

iTrader: (96)

Cant you do an idle relearn on f bodies by unplugging the tps, turning the ignition on for 1 minute, then shutting it off and replugging the sensor back in?

ringram

just pull the pcm fuse...

jimmyblue

iTrader: (11)

You can't check for vacuum leaks with the IAC plugged
in because it will fight any change faster than you can
hear RPM dip - especially if it's already surging. Get it
running and pull the IAC connector, it should just stay
put at whatever RPM. Now the PCM won't be working
to hide any RPM change.

I prefer propane for leak checking, you're not stuck with
line-of-sight (-spray), which can miss things like the
underside of manifold runners. Got a weed burner that
I took the head off, nice long neck and a straight stream
of the gas.

johnson73801

iTrader: (3)

if you are doing this without scan data you can try unplugging maf.. if it smooths its probably dirty or shot. thats what mine was. but also ran into one that the iac screws backed out and it couldnt adjust to compensate. but also agree with out computer data its all a quess.