Idle Adjustment Problem

After dropping in my new engine and working the problems out, I’m left with this; I still have a high idle “hot” or cold”.

The timing is set at 10° BTDC and the car idles at around 1400 rpm in park. I tried adjusting the minimum idle by: linking the “A” and “B” terminals under the dash via the diagnostic port, turning the ignition to on for 30 seconds, unplugging the idle air control valve connector, starting the car, and backing out the throttle adjustment screw.

The throttle blades themselves only moved very slightly while the adjustment screw started to move away from contact with the throttle. They appear to be closed visually and cannot rotate any further. The TPS is properly lined up. Idle only dropped about 100 rpm.

My guess is that I may have a bad IAC valve. Any suggestions?

I have a new 10.5:1 compression 383 speed density tuned port injection motor:
Prepped 350 4-bolt main block
Eagle internally balanced rotating assembly
Wisco pistons
Trick Flow aluminum heads (195)
Comp Cam hydraulic roller cam:
Comp Cam XR276HR, duration advertised in 276 ex 281 @ 0.050” in 224 ex 230, lift in 0.503 ex 0.510, lobe 112°
Comp Cam roller lifters and rockers
Accel ported intake base
AS&M intake runners
Ported plenum
Ford 30# injectors
New distributor, rotor, cap
All new sensors
Etc.

Original set-up was a 305 sd tpi all in my 1991 Trans Am.

 

So, what did you do about the 305 ECM? You have a 383 now (and I think you will really love it once you get it to run correctly, as I love my 395).

You need a custom Eprom chip to run that thing right.

The biggest problem that I had with my 395 was user caused vacuum leaks. Once I got the vacuum leaks identified and sealed and completed the minium idle routine and set the static timing correctly, the engine idled very nicely. And it did not hurt that I program my own Eproms.

 

I had a chip burnned per my engine specs, enough to get me going and in the spring I'm going to get it dyno tunned. It runs very smooth and I know traction will be a major issue.

 

Some people have gotten the runners/gaskets mixed from side to side and that cuased a very high idle. Just check for vacuum leaks. Could even try blocking the TB off with a stiff board or plate, and see if it still idles. It might let you hear where the leak is.

 

Thanks, I'll give that a shot.

 

Just as a reminder, you should be using a separate diagnostic tachometer, and not a dash mounted unit to test/set the minimum air RPM.

Good places to look for "hidden" vacuum leaks are EGR, PCV, loose trim plate on the TB, debris preventing the IAC from closing fully, and the brake booster.

 

Thanks again, I'll look into all of this in hopes of finding something good.

Jim