1990 Chevy 1500 pickup 5.7 liter V8 it starts fine but wont idle if you give gas its let goes from a low to high couple times then dies is the ecmchip?

It's highly unlikely that a bad ECM chip is the sole cause of your 1990 Chevy 1500's problem. While a faulty ECM *could* contribute, the symptoms you describe (starts fine, revs high then dies) point to several other more common issues first.

Here's a more likely breakdown of potential culprits:

* Idle Air Control (IAC) Valve: This is the most probable cause. The IAC regulates air flow at idle. A dirty, sticking, or faulty IAC valve prevents the engine from maintaining a consistent idle speed. Cleaning it is often the first step.

* Throttle Position Sensor (TPS): The TPS tells the ECM the throttle's position. A faulty TPS can send incorrect signals, leading to erratic idle and stalling.

* Mass Airflow Sensor (MAF) Sensor: (If your 1990 model has one, some didn't). The MAF measures the amount of air entering the engine. A dirty or faulty MAF sensor will give the ECM incorrect data, affecting fuel mixture and causing idling problems.

* Vacuum Leaks: Vacuum leaks disrupt the engine's air/fuel mixture. Check all vacuum lines and hoses for cracks, leaks, or loose connections. Pay close attention to the intake manifold gaskets.

* Fuel Pressure Regulator: A faulty fuel pressure regulator could cause inconsistent fuel delivery.

* Distributor (If equipped): Issues with the distributor cap, rotor, or ignition coil could lead to misfires, especially at idle, resulting in stalling.

* Cranking Sensor: A faulty Crankshaft Position Sensor prevents proper timing signals, impacting idle and overall engine function.

Before Replacing the ECM:

1. Check for Diagnostic Trouble Codes (DTCs): Your 1990 Chevy likely has a method for retrieving trouble codes from the ECM. A code reader (available at auto parts stores) can help diagnose the problem.

2. Clean the IAC valve: This is a cheap and easy fix that often solves idling problems. Spray it with throttle body cleaner and work the valve manually to remove buildup.

3. Inspect vacuum lines: Carefully check for cracks or loose connections in all vacuum lines.

4. Test the TPS and MAF sensor (if applicable): These often require a multimeter and some knowledge of testing procedures. Consult a repair manual for your specific vehicle.

Replacing the ECM is a last resort and more complex. It's best to systematically check the more common and easily accessible components first. A repair manual specific to your 1990 Chevy 1500 5.7L will be invaluable in diagnosing this problem.