With my new H/C/I combo, it idles at 750 in park. My IAC is clean, and completely maxed (160 position at idle) to hold the 750 rpm idle. It idles great at 750, but when you put it in drive/reverse, the rpms drop to around 600 and the car wants to stall. Ed Wright told me at this point, you have to raise your idle with the screw in the throttle body. Just curious as to what you guys think. Thanks

Most EFI systems idle at around 1000 rpm. I think 750 is too low.

For whatever reasons, if you need to increase the idle speed, adjusting the screw to open the butterflies is the only way.

What camshaft? What converter stall?

Camshaft: http://www.compcams.com/Cam_Specs/Ca...?csid=188&sb=2

Stock 1600 stall. I am going to do gears and a stall. But I just finished the engine yesterday.

what do you base this statement on?
stock tpi could be made to idle at 450 rpm, at least in a brand spanking new 87 firebird...

my lower limit is around 600. my cam wont let me go lower than that without randomly shutting off.
i keep mine at 700 warm 650 cold.

When stock, my TPI idled at 1000 cold/750 warm in park and like 650 in drive. The new combo does not like this 650, lol.

i guess it depends on the condition of the motor and related components.
my uncle bought a 87 firebird brand new back in 87 when he graduated college.
his had a 350 tpi and he told me about how he could turn the idle down to 450 just for fun.
his car was a bit peculiar though i guess.
apparently he had a dual fan setup that never turned on... even from day one.
he said that when he was driving it home, he noticed the temp gauge pegged at 260 after sitting in traffic, and the fans werent on.

point is, quality control in the 80's isnt what it is now, and its entirely possible that some cars came drastically different than others straight from the factory.
is it possible that one 350 tpi will idle at 450 with ease, and another struggles to hold 750, of course.
i dont know if the change to speed density had anything to do with it, but that is another factor i suppose.
FWIW, my owners manual specs idle at 600 rpms in gear

My IROC idles at 750 in park and about 600-650 in drive. I thought it was a little low but it seems fine so far. I have put a lot of mods into the engine etc. check out my Stats! I also got a custom chip from Ed Wright. Now if only I could only figure out my starting issue.

I'm new to the TPI world but in reviewing literature (article in Hot Rod) and the Factory Shop Manual for my 1988 GTA 350 (57,000 miles) the adjustment of the idle speed involves more than just adjusting the position of the throttle plates. I also thought that my idle speed was low in drive (750 rpm neutral) so I adjusted the TPS using the shop manual instructions which involves setting the correct timing first, putting the computer in diagnostic mode, unplugging the IAS, setting idle speed with the screw adjuster (I think the factory setting in this mode was 450 RPM in neutral), unplugging the timing wire from the distributor (had a heck of time tracking that one down) then measuring the voltage coming from the TPS at idle. To further check the condition of the TPS you can view the voltage rise as the throttle is opened. Voltage reading at idle for the 1988 is .5 volts.

Before starting any of these procedures I performed a complete tune up of the ignition system (cap, rotor, wires and plugs) and cleaned the fuel system by using 3M's DIY fuel injector cleaning system.

This seemed to help but honestly after it was all said and done the idle speed remained about where it was before I started but the engine certainly was crisper and runs even better than it did before I started.

Good Luck!

The idle speed is set in the engine computer and the engine computer tells the IAC valve to make adjustments until that rpm is reached.

And the engine computer would detect a change in the park/neutral switch and then lower the RPMs to put less wear on the transmission.

Or if it detects that the A/C is on, it will increase the idle speed to provide additional power.

Various engine computers have inputs for various things like A/C, headlights, rear window defrost, heater fan on high, electric engine cooling fan on, etc. and when these things are running, it will up the idle a bit. Some will detect a drop in voltage because an energy hog has been turned on and then increase idle to increase the alternator output (may be newer vehicles only???).

But the question is if it will also increase the idle speed when out of park or neutral and one of the above is also on?