Recently completed a head/cam swap on my 88 GTA, 350 engine. Heads are vortecs, cam is GM lt4 hot cam, SLP runners and a SDPC vortec/tpi base. Custom chip from PCMFORLESS. My question is regarding idle speed. When cold, desired rpm shows as 1182 RPM, using my Auto Xray EZ Link scanner, and actual rpm is around 650 and fluctuating, car wants to stall. As the engine warms up, the desired rpm slowly drops to 900 and the actual rpm increases to 850, still fluctuating. Tuner said to expect 850 or so when warm, so that is in the ballpark. Should I start with the "minimum air" adjustment? Should the spec for this adjustment still be 425 +/- 25 rpm? At present, fuel pressure is 43 psi, vacuum disconnected, TPS is at 0.54 v (engine off) and 0.56 v (engine running), vacuum is 15 inches and timing is set at 8 degrees advanced.

 

What are the IAC counts doing from cold start to best idle. They usually start at 140-160 and drop as the rpm raises and raise if rpm is below target speed.

A normal cold start would be 160 (depends on the bin) and expect a change in IAC steps (down) with every drop in target rpm till at hot idle where they are at about 40 steps or so.

 

Here is some data. Before startup, I measured the intake temp, it was 65.5 degrees, the CTS showed 65.3 and the IAC was at 144 (engine off). I started the engine, IAC went to 160, desired RPM was 1162 and the actual RPM was 875-911. After 2 minutes, CTS was 107, IAC still at 160 and Desired RPM was 1100, actual RPM was 650 - 700. After 4 minutes, CTS 132, IAC 120, Desired RPM 987, actual RPM 1000-1050. After full warmup, CTS 198, IAC 66, Desired RPM 900 and actual RPM 860-920. In closed loop at that time.

 

You need to open the min air up, the screw that is the throttle blade stop.

This will raise your idle rpms and lower the IAC steps.

You can use a small washer or screw driver blade between the arm and the stop, just for a quick check.

After changing the stop position recheck the min TPS volts, more air means more volts. Reset to .54 volts.

 

Thanks, I will try that this morning. After the neighbors wake up.

 

Did the idle setup this afternoon. Could not get it to idle below 500-450 rpm. Seems to run smoother, still not right, but better. Will check the cold idle tomorrow morning.

 

Set your min idle when warmed up to the idle rpm in the chip

 

Would that be the desired RPM value when warmed up? If not, where can I find that value?

 

The idle at 500 is fine for the min rpm, if you have an auto 550 rpm in gear.

A stick will be higher, as will park and neutral. Min idle rpm can be set 50 rpm below the normal idle.

Mine idles at 650 P/N and 550 in gear, much below that and your Alt wont be charging as much and oil pressure starts to drop. Also need vacuum to run things.

 

Yes

 

Tried the desired RPM value ( 900 rpm when warmed up) and took the car for a ride. Didnt like the adujustment, car would not idle below 1200 after all components re-attached. Re-adjusted the idle to 650 rpm, re-attached all the components and car idles around 950 in neutral and 850+/- in gear. Think that is the sweet spot for this combo. Time to continue on with the fine tuning. Thanks, for the help.