Here's a breakdown of troubleshooting and potential fixes:
1. Diagnose the Cause – Don't Just Adjust: Before attempting any adjustments (which are unlikely to help and could harm your engine), you need to identify why the idle is pulsing. The most common causes are:
* Vacuum Leaks: Check all vacuum lines for cracks, loose connections, or holes. Pay close attention to the lines going to the brake booster, the intake manifold, and the EGR valve (Exhaust Gas Recirculation). A simple spray bottle with carb cleaner (carefully!) near suspect lines can reveal leaks by causing a change in idle speed if sprayed near a leak.
* Dirty or Faulty Idle Air Control (IAC) Valve: This valve regulates air entering the engine at idle. A dirty IAC can stick or cause erratic air flow, leading to a pulsing idle. Cleaning it with a suitable cleaner (often carb cleaner) is a good first step. If cleaning doesn't resolve the issue, it might need replacement.
* Dirty or Failing Throttle Position Sensor (TPS): This sensor tells the ECU the throttle's position. A dirty or faulty TPS can provide inaccurate readings, causing the ECU to adjust the fuel mixture incorrectly. Cleaning the TPS with electronic contact cleaner is recommended; replacement may be necessary if cleaning fails.
* Mass Air Flow (MAF) Sensor Issues (If Equipped): Some 1987 Nissan pickups might have a MAF sensor. A dirty or faulty MAF sensor will cause inaccurate air flow readings, leading to a poor idle. Cleaning (with MAF sensor cleaner, *not* carb cleaner) is recommended; replacement may be needed.
* Faulty Engine Control Unit (ECU): While less common, a faulty ECU can cause a range of problems including idle issues. This is usually diagnosed last after other components have been checked.
* Fuel Delivery Problems: A clogged fuel filter or other fuel delivery issues can also lead to an erratic idle.
2. Troubleshooting Steps:
1. Visual Inspection: Start by visually inspecting all vacuum lines, the IAC valve, and the TPS. Look for anything obviously damaged or out of place.
2. Clean IAC and TPS: Clean the IAC and TPS with the appropriate cleaner. Refer to your vehicle's service manual for specific instructions and precautions.
3. Check Vacuum Lines: Carefully inspect and test all vacuum lines for leaks as described above. Replace any damaged lines.
4. Check Fuel Filter: Inspect and potentially replace the fuel filter.
5. Advanced Diagnostics: If the problem persists, you may need to use a scan tool to read diagnostic trouble codes (DTCs) from the ECU. This will help pinpoint the exact problem. A qualified mechanic will have the right tools and knowledge to interpret these codes.
3. Important Note: There's usually no "adjustment" for a pulsing idle on a fuel-injected engine. The ECU manages the idle speed based on various sensor inputs. Focusing on fixing the underlying problem is crucial, not attempting to force a change.
If you're not comfortable working on your vehicle's engine systems, take it to a qualified mechanic. Improper adjustments or repairs could cause further damage. A service manual specific to your 1987 Nissan Pickup will be invaluable in this process.
