92'STOCKER

My 92 Z is stock with a 5.7. Here's the problem I am having intermittently; the car will crank but not fire until I pump the gas. It will then start, but I have to keep feathering the gas. It will die when you make the first couple of stops and then runs normally. I had two different shops look at it and neither could find an issue. Here are the items that were checked. Fuel pressure, hooked up and analyzed, no codes, clean fuel. Half of the time it starts instantly, the rest of the times it's a pain. Thanks for any help.

92'STOCKER

My IAC valve plug is covered in oil. Is this normal or is there an o ring that may be damaged?

jaychevyman

I would start by checking the pcv vavle and verify that there is vacuum. Just pull it out while the car is idiling and put your finger over the inlet...your car should want to die if its good. I had the same problem with oil all over my air filter as well. Turned out bad pcv and a clog backed up all the way into the intake manifold..Just drilled it out

TwinTurboROC

1 Clean up the IAC plug, and check and make sure there is a good connection to the IAC. There is an article on how to clean the IAC, its a good place to start. I will post it below this.

2 How is the tune up?

3 Does this happen at specific Motor temperateures? Outdoor temperatures? You have a typical bad coolant temperature sensor complaint on the simple end.

Idle Air Control Cleaning

You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.

DON'T do what I did the first time! I removed the IAC, plugged it back in to watch operation, then turned on the ignition. The IAC stepped the pintle out to full extended position until the spring took over and launched the pintle across the garage. A while later, after moving a couple of other cars and several pieces of equipment, I found all the parts I needed to reassemble the unit.

You can gently rock the pintle back and forth and allow the spring to extend it until it comes apart in your hands. Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation.

When the worm gear on the pintle shaft is clean and dry, apply one drop of clean light oil to the shaft and work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.

While the IAC is out, clean the air passages in the throttle body. The oriface in the TB where the IAC resides is the seat that the IAC valve closes against, and it can accumulate a lot of carbon, dirt, and debris. The easy way to do this is with carburetor cleaner and a small stiff brush. Another "DON'T" - don't use your sister's toothbrush.

When everything is clean and dry, replace the gasket if it is damaged, apply a little anti-seize to the threads, and torque the IAC to the proper specs. (13 ft/lb for '85-'89 , 30 in/lb for 1990-on.) Proceed with setting the TPS and minimum air position.

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Cut and form a paper clip into a "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' sockets. Turn on the ignition, but don't start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. Under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector is your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.

Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400 RPM with the transmission in "DRIVE" on an automatic transmission car, 450 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.

Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.

-courtesy of lord Vader

Azrael91966669

i will agree check the iac

92'STOCKER

Thanks for the input everyone:

1 Clean up the IAC plug, and check and make sure there is a good connection to the IAC. There is an article on how to clean the IAC, its a good place to start. I will post it below this. (I am going to buy a new one to eliminate any doubt)

2 How is the tune up? (74,000 original miles, plugs, wires, etc. changed at 60,000, scoped twice in last year and everything is good)

3 Does this happen at specific Motor temperateures? Outdoor temperatures? You have a typical bad coolant temperature sensor complaint on the simple end. (Temperature does not seem to be a factor. This has happened in Phoenix and in California in different seasons.)
Idle Air Control Cleaning

You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.

Can the IAC be removed without removing the throttle body, I don't see a way to get a wrench in the area?

TwinTurboROC

You have to remove the TB. Easy 5 min job. U can re-use the tb gasket. Try cleaning the iac first. Also clean the tb since you'll have it off.

92'STOCKER

New IAC valve, cleaned the Throttle Body, 180 deg. thermostat, changed the bypass hoses.

Car starting fine so far! Thanks for the help.

Unfortunately I found another problem after cleaning everything up; the intake manifold in the drivers front corner is hissing when I turn the car off. When I put water on the area it bubbles. I had the gaskets changed around ten years ago for a leak in the exact same area! Any suggestions to keep this from happening again? New manifold?