camz383

Hi all,

I am having some trouble with the idle on my Z28 which I hope someone can atleast help point me in the right direction on where to start troubleshooting.

When I first start the car cold, the idle drops to about 500 RPM and will sit there and bounce around a little bit. If I hit the throttle a little bit and rev it up, the idle then jumps to 950 RPM and will idle pretty decently.

From there once I take off and drive around a little I have been experiencing some terrible idling. It drops down to about 500 RPM and then eventually will die if I do not repeatedly give it gas. Unlike when it is cold, reving it does not help, after I rev it, the RPM will drop back to about 500 RPM and it will eventually cut out.

I am in search of some help on where to start looking. I know about checking the TPS voltage, which should be correct, but I havent checked in about a year. I did the modification so I could adjust the position by slotting the mounting holes.

My set screw on the TB is cracked open quite far (almost all the way the screw will allow), can this be part of the cause? Should I drop the set screw back to closed off and then procede from there on adjustments?

Thanks for all the help!

95Blackhawk

Do you have the ability to datalog? I use Datamaster. With such a nice setup, that is radical from stock, you really need this software. It is just part of the cost of producing more HP effectively.

Injuneer

What RPM did the tuner set the idle to? A4 or M6 - that will help determine the correct idle setting?

Sounds like the IAC motor is not responding, or the IAC passage in the TB is plugged. Did it ever idle correctly? If it did idle correctly earlier with the same setup and tune as you have currently, that would rule out tuning problems, related to an agressive cam.

You really need to provide more details on the engine mods.

Scanning/datalogging it is pretty much the only way to go. That allows you to examine the TPS voltage, IAC counts, idle air flow, coolant temp sensor, MAP, timing, etc, all of which can affect the idle.

camz383

I have a PCM4Less tune and he set the idle at 950rpm for my M6.

The car did idle nicely at one point, even after the new tune.

My mods are as follows


ENGINE

383 stroker
Scatt 9000 crank
6.0" rods
Srp forged flat top pistons
Race prepped and race balanced using race quality bearings
Custom Comp cams camshaft(nitrous stick)

CAM SPECS

Gross lift .540 intake and .562 exaust
duration @ 50 ... intake..242 and exhaust..248
Lobe seperation 113.0

MISC. SPECS

Stock casting heads
Cut for 2.02 * 1.60 manley sportsman valves
Comp Cams 650 lift springs
Mildly ported
Bowls smothed not cut into
Intake smothed not cut into
Vaccuum canister (brakes)
Mezerie electric water pump
Cloyes true double roller timing set
Comp Cams lifters and pushrods

IGNITION

Taylor custom over the valve cover wires
Billet wire looms
NGK TR6 plugs
MSD Digital 6 Ignition

INDUCTION

Holley 58mm Throttle body
Arizona Speed and Marine CAI
Trick Flow ceramic coated intake elbow
Stock Ported mass air meter

EXHAUST

Flowmaster 40 series
Custom Y pipe
Hooker long tubes Jet Hot coated

FUEL SYSTEM

42lb Racetronix injectors
255 ltr Motorsport in tank pump
Adjustable pressure regulator

NITROUS

Nitrous Works Wet set up
Nozzle injection
Custom electrical for safety
75 to 175 adjustable

camz383

You say that the coolant sensor can affect the idle??? I may have just found the culprit! I have a low coolant light on, yet my coolant is full...

A bad sensor can cause the rough idle??

bw_hunter

The low coolant light is driven by a sensor on the radiator. It doesn't report to the PCM, only to the light on the dash. Unfortunately, it isn't the problem in this case.

rclearyiii

Temp coolant sensor can affect idle...not the coolant level sensor.