Whisper

iTrader: (12)

So I have a M6 98 Z28 with some MMS 220 heads, a 226/230 cam, FAST 92mm intake, etc. I had the car SD tuned for the heads and cam and the car always ran great. But, back in April, I had the car retuned for the Fast intake install (previous was an LS6 intake), changed the plugs to BR6s, and went to 42 lbs injectors instead of the original 36s. Tuning was done at the same shop. The car idled and drove fine for a month or two but now every morning for the past 3 or 4 months the car wants to die at every stop. The odd thing is that it isn't immediate. Backing out of my driveway and the first two stop signs, the car is fine- maybe the occasional stumble. But like clock work by the third stop and for the entire 2 miles to work, the car is dying at every stop unless I feather the throttle. As long as I'm moving, the car runs perfectly. Its only when the car needs to idle at a stop that it wants to instantly cut off. Allowing the car to warm up doesn't seem to help either.

After the car has pulled this stunt the entire way to work and died 6 or 7 times if I drive it anywhere else, its perfectly fine. Its as if the idle issue never existed. I'm not sure how long the car has to sit before the problem arises again but its always back to the same issue by the next morning. I know SD tunes can be weather sensitive but this problem has persisted through the summer, not the winter. Could this be some form of idle relearn issue? Could it be a vacuum leak? Is there anything to check for before I call the tuner back up and have them fix it?

JakeFusion

iTrader: (7)

Well it could be a few things. Without being able to data log, it's a shot in the dark along the lines of airflow is now off (FAST manifolds leak... ask me how I know) and the injector tuning could be off.

Or it could be the IAC tuning and Throttle Follower/Cracker tables are jacked up with the 92mm TB, which would pose airflow problems (the IAC port on the FAST brand is smaller than stock, so you have to tune the IAC more aggressively to allow enough bypass airflow). If it's dying even when warm, it leads me to believe you need to crack open the TB blade more (and retune the RAF/base airflow) and tune the follower so it allows more bypass airflow in the <1600 columns to keep the car from stalling out.

Whisper

iTrader: (12)

Thanks for the reply Jake. The car doesn't have a high dollar 92 mm TB (I refused to get gouged for something so simple) but I am using the best of what was available on Ebay. The seller even seems to be gaining a following on External Engine.

One thing that I did change eventhough the car had problems before and after is the rubber hose connecting the Fast to the TB. The first one I got and that the car was tuned with was a ribbed and angled rubber hose. In retrospect, it was the stupidest purchase I could have made considering the rubber is flexible and ribbed.

I changed this out for a straight and ALOT more rigid intake hose from intakehoses.com. But it did not resolve the idle issue.

Boosted53F

if your SD ... mechanical changes before the TB would not be your issue. A correct SD tune with your pcm should not be weather sensitive. Maybe your tuner missed something. If you clear fuel and idle trims by disconnecting battery does it seem to idle and drive better on startups for the first few drives?

-have tuner check to see if adaptive idle is turned off. If your PCM has a SD operating system written then you wouldnt have this.... but just check.
-how do fuel trims look with LTFT turned off?
-do you have access to a wideband?