bigken

iTrader: (8)

Ever since I had my Trans Am tuned for the converter I started having problems with the idle air control. I have taken it to a shop to be fixed and now I am not getting any codes for the IAC but when the car is cold the RPM's surge up and down and will constantly stall out until they finally catch. Even then for the first few minutes will driving it will stall out once or twice. When the car is warm it really doesnt do it, but if it has been sitting for more than an hr or so it will. I do not really drive the car all that much but no matter how many times I take this to get fixed I am having the same problem, does anybody know what may be causing this? Does this need a re-tune? I never had this problem before the converter.
thanks for any help!

98z28bitcha

iTrader: (22)

I would say It's something with the tune.

bigken

iTrader: (8)

I guess I will just have to get it re-tuned but I have no idea why getting a tune for the converter would affect this?

jimmyblue

iTrader: (11)

Lower converter mass makes the setup less forgiving
of other errors. I would bet your idle mixture is over-
rich (esp. if there's a cam in the picture).

bigken

iTrader: (8)

yes it has a comp cam with 566, 568 lift at 222/224 duration and the converter is a FTI 3600. Upon initial startup the car blows black smoke and the wall where the *** end meets the garage is covered in black. I was told that they tend to fire up a little rich when they are cold, is this true?

Mart00SS

iTrader: (19)

When the engine is cold it does require a slightly richer mixture to run properly but blowing black smoke on startup?.... NOT normal.

Im not sure who said that was ok but it sounds like you may need to find a new tuner.

bigken

iTrader: (8)

Im not sure who said that was ok but it sounds like you may need to find a new tuner.[/QUOTE]

Yea you are probably right

maverickmk

iTrader: (10)

The black smoke means it's running too rich.

bigken

iTrader: (8)

could that also mean that I have some fouled out plugs?

maverickmk

iTrader: (10)

From running too rich. Unless you have some problems with the heads leaking oil into the combustion chamber.

bigken

iTrader: (8)

I am installing a new suspension this weekend and I am going to pull the plugs and replace them since the car has had a few crappy tunes and the plugs have never been changed. It cant hurt and for what it is going to cost it will be cheap insurance, all i have to do is find someone somewhat local who can tune it.

jimmyblue

iTrader: (11)

Cam like that makes an over-estimated air mass at low
RPM. That overfuels the motor to begin with.

The elevated idle MAP when cold, indexes you into a
higher open loop enrichment. Compounded by airflow
errors.

Overfueled means the motor is slow to respond to IAC
air changes so the RPM control loop becomes unstable
and over / undershoots.

Getting the low end airflow metering right is job 1, and
then shave back on the EQ vs ECT vs MAP table to
get a lesser enrichment (once you have the basic facts
straight, air-wise).

bigken

iTrader: (8)

Can you recommend someone who could fix it? Right now my garage wall is covered in a black soot or carbon and the fumes could kill you. What I don't understand is that aside from running very rich becauase I have had the black smoke issue for awhile I never had the cold start issue until the stall?