1G Cold Idle Surge

[hazzard74]

So I have the dreaded cold idle surge. After it warms up, idle settles down and all is well.
I have searched and read many pages on the subject and I know it could be a few different things.
Here’s the thing: when I ground out the timing plug the idle immediately goes back to normal. And when I remove it, begins surging again.
Anyone know if is this a tell-tale sign of a specific failure?

 

[Tyeler18]

Do you still have the coolant hoses on the throttle body? Grounding the IAC just locks it in place, which is probably why it smooths out, and also sounds like your IAC is functioning fine. If you don't have the coolant hoses, is your FIAV properly blocked off? 95% of cold idle surges on dsms that come through my shop are a stuck/improperly blocked FIAV.

 

[hazzard74]

Yep, all of the hoses are connected. I just finished an engine swap. Thing is, I used the intake and TB from the old motor and never had this problem before.
Is it possible there’s an air bubble up there that’s messing this up?

 

[pauleyman]

Check for leaks

 

[Tyeler18]

BLT would be a good start. Have you set base ignition timing and set base idle as well? How long was the throttle body off before you finished your swap? Coolant sitting in the valve could very well have dried up and seized the valve if it sat long enough without fresh coolant circulating through it.

 

[hazzard74]

This is a non-turbo car.
BISS and timing both done.
TB sat in the garage for about 2 months dry.
Can the FIAV be cleaned if it is just dried up coolant?

 

[Tyeler18]

I would think it could be pulled apart. I've always just deleted them but closing the valve and deleting the lines, so I can't say for sure. I will say the valve is calibrated though so pulling it apart would require some way to mark it's position otherwise you'll spend a lot of time messing with it to get it calibrated again.

 

[hazzard74]

Thanks for all the help.
It’s nice to have a better idea as to where to start.

 

[steve]

Here’s the thing: when I ground out the timing plug the idle immediately goes back to normal. And when I remove it, begins surging again.

I'd have to go back and read the ECU code but I wouldn't be surprised if the ECU routine that causes the idle surge behavior isn't disabled during the timing adjust mode. (Explaining why it goes away) Idle surging is caused by the ECU when engine running faster than the code thinks it should, while the idle switch is closed, and is part of the deceleration fuel cut routine.

If the car stops (idle drops) once the coolant heats up then the FIAV is doing it's job (mostly) and you should look at the whole system since little changes in the idle air bypass make big differences in actual idle speed.

 

[hazzard74]

Started with the FIAV.
The plastic plug under the freeze plug is stuck. Really stuck. Have it soaking in PB at the moment hoping that will help.
Any other tricks/tips on how to get it screwed in?

 

[Tyeler18]

I've never gotten one to free up when they're stuck. I let one soak for a week full of aerokroil, pb blaster, etc