Possible causes for high idle in a 1987 Chevy van:
* Fast Idle Cam: Older vehicles, especially those with carburetors, may have a fast idle cam mechanism. This cam is designed to keep the engine running at a higher RPM when cold to help it warm up quicker. If the cam is sticking or malfunctioning, it might keep the engine at a high idle even after it's warmed up.
* Vacuum Leak: A vacuum leak can disrupt the air/fuel mixture, causing the engine to run rich and possibly increase idle speed. Check for cracked or loose vacuum hoses, especially those connected to the intake manifold and carburetor.
* Choke Problems: If the choke is stuck in the closed position, it will restrict airflow, leading to a rich fuel mixture and high idle.
* Dirty Idle Air Control (IAC) Valve: If your van has a fuel injection system, a dirty IAC valve can cause it to stick open, resulting in a high idle.
* Throttle Position Sensor (TPS) Malfunction: A faulty TPS can send incorrect signals to the engine control unit (ECU), leading to an irregular idle.
* Engine Sensors Issues: Other engine sensors, such as the oxygen sensor or temperature sensor, can also influence the idle speed if they are malfunctioning.
* Improper Fuel Mixture: If the fuel mixture is too rich (too much fuel), it can cause a high idle. This could be due to a faulty fuel pressure regulator or a dirty fuel filter.
How to troubleshoot the problem:
1. Check the Fast Idle Cam: If your van has a fast idle cam, make sure it's functioning correctly and not sticking.
2. Inspect Vacuum Hoses: Check for any cracks, leaks, or loose connections in the vacuum hoses.
3. Examine the Choke Mechanism: Make sure the choke is opening properly and is not stuck in the closed position.
4. Clean the IAC Valve: If your van has a fuel injection system, clean the IAC valve with a specialized cleaner.
5. Check the TPS: Use a multimeter to test the TPS for proper voltage output.
6. Inspect Engine Sensors: Check other engine sensors for proper operation using a multimeter or scan tool.
7. Adjust Fuel Mixture: If necessary, adjust the fuel mixture to ensure it's within the proper range.
Important Note: If you are not familiar with automotive repair, it's recommended to take your van to a qualified mechanic for diagnosis and repair. They can use specialized tools and knowledge to pinpoint the issue and fix it properly.
