recently (nov-dec) replace the top-end on the motor. heads, cam, everything. went with a weiand intake. kept having idle problems (rpm's would hang momentarily while accelerating when parked, tuner unable to get the rpm's below 1000, engine would sometimes surge when i turned on the heat/air, and the rpm's would stay high while it was moving) that seemed to be related to unmetered air. my tuners says that the iac keeps kicking in to compensate for the air.

tried to re-seal the weiand and the problems were still there. blamed the weiand and went with an ls2/ptm set-up. did the install. same thing (idle problems) as before.

found a cracked vacuum line that ran from the intake to the "t" by the pcm. repaired it. now the problem is a little worse. decided to plug all vacuum related ports on the intake to see how it would behave. still the same.

now something that i dont understand......i have the vacuum line plugged that runs to the hvac control, but the engine will still surge when i turn the ac/heat on. now if i pull the fuse it wont surge. this has me really confused. how can it still surge if there is no vacuum running to it?
anyone that might have a idea as to what my problem is, please let me know.
i just want to be able to drive my car again.

 

no opinions on this?

 

the surge you get from turning the a/c on, is coming form the compressor adding a load to the motor, and it doesn't like it. I'm gonna guess that you have tuning problems, if you are 100% that you plugged every possible vacum source on the motor and intake, and have still got surging issues it's probably tune related.


What did you put on for a h/c setup? A big cam, is gonna have some surge... how much usually has alot to do with the tune

 

heads are just hand ported/opened up with 2.02's/1.60's & 918's, f-13 cam, type r lifters, harland adjustables. and i am sure that all sources of vac/air are plugged. the surge i mentioned happens any time i use the hvac control at all. not just the a/c. i am just extra confused as this has happened with 2 different intakes.

 

Several of the heat modes, like defrost and bilevel
at least, do run the compressor. Compressor adds
drag torque and the PCM tries to model it, but on
a high-mods car the torque-airflow relation and the
airflow value itself have to be suspects. The vacuum
operated diverters would present an air surge to the
manifold and perhaps bother fueling and RPM, but
I think only if the thing was not robust to begin with.
Like it was already over-lean and you snuffed it. If
rich the RPM would surge with a shot of air and
lean it will drop. Here you have to distinguish the
initial response from the yo-yoing that may ensue.

Presumably you are confident about the MAP and
vacuum port seals at the back of the manifold,
and have chased down every line. Might not hurt
to plug it all at the source leaving only the MAP.
Check and maybe cap both of the PCV ports
(manifold and TB).

Now one thing that might be good to do is use
bidirectional controls to direct-set the IAC
position (aim high if in doubt) and step up to
not-nice and down to can't-live. Open loop
idle should hold a steady RPM with a steady
airflow. Now if you have instability look at who
is doing it. The RPM-loop spark control could
play badly with you; you can flatten that out
and the loop gets even more opener Still
got a wandering idle? Look at the O2 sensors,
proportional fueling, and like that; put fueling
open loop by the ECT threshold and now you
should be full rock steady, wherever the IAC
puts you. Now you can look at the fueling;
clean or whack? Timing, low or high? Bump them
individually, learn what it likes and make the
changes.

All tedious time consuming stuff that you would
really rather do as a hobby than pay shop rates
for, unless you are one rich sumbitch or work
there.

The motor wants to run, it's just that prancy
he-bitch of a PCM won't fvcking shut up long
enough to get its mind right.