For the past few months, my car has had intermittent voltage drop issues where it would randomly stop charging altogether. I recently replaced the alternator and that seemed to have fixed that issue.

However, now when I start up the car when it's cold, the engine will sometimes sputter, catch itself from stalling, and the idle will fluctuate between 700-1300 rpm for the next few minutes. It will eventually stabilize around 1000, but the idle will still dip too low sometimes and want to stall when on the brakes approaching a stop. The deceleration when letting off the gas doesn't sound smooth.

After driving around longer and the car is fully warmed up, the problem goes away. The idle won't hunt anymore after starting when the engine is still warm as well. Turn the car on after it's cooled off and the problem returns. I have a Power FC and haven't touched any settings on it. What could be the issue?

Thanks

 

Sounds like you need a tune.

 

Did you cut the 4 wires necessary upon PFC install, or are the pins removed (I don't recommend this second option)?

Have you set the TB properly? Ie air bleed screw, idle adjustment screw etc.

Also, go into the 'sensor/switch' menu on the commander and check your VTA1 and VTA2 voltages with the throttle closed. If the TPS is out of spec you'll have issues. From memory, you want 0.40 and 1.00 to be completely in the middle of the ranges, which are 0.10 to 0.70 and 0.75 to 1.25.

Let us know what's up, Canuck!

 

The car came with the PFC already installed and had no issues prior to my voltage drop problems. I haven't adjusted any TB screws.
Unfortunately I don't have a commander so I won't be able to make the changes myself. Perhaps I could borrow a friends and check out what the values are.
Could the voltage drop problem I had somehow make the PFC lose it's tune?

Thanks for the responses!

 

Yep. Stop ******* around and just get it tuned

 

I have very similar issues, also running a PowerFC (base map) but fingers crossed, after going through the rats nest just last night, it seems to have been mostly resolved.
My mods are minimal, catback, dp, 99 spec turbos.

During my troubleshooting, I had tried the disable O2 F/B and idle control features in the PowerFC but it did not help with my hunting idle (they are done through the commander fyi).

I did verify the TPS voltages via my commander (before I installed it, I stuck a pin into the grommet for each wire on the back side of the connector and took readings from there). Since it's a cold start issue, you'll have to actuate the fast idle cam (replicating the wax rod being warmed) when taking the readings, otherwise your voltages will be skewed high.

I got some idle fluctuation when the air screw (flat head recessed in the throttle body) was closed (at 1/4 turn) a little too much. I opened it up a bit more (probably at 3/8 turn) and on cold start this morning, I noticed it hunting just the tiniest bit (between 950 and low 1000s). I may try to adjust a little bit more open again to see if it resolves the issue.

I hope it's something simple like mine. good luck!

 

Valuable info - cheers! Hopefully we both solve it fully