The engine will not idle smoothly
Symptom: The engine will not idle smoothly, or it stalls during idle when the engine is warm. When the engine is warm or hot and you take your foot off the gas pedal, the engine runs very rough and may even stall. When you run the engine at higher speeds, it seems to run fine.
1. If you have a carburetor (gramps), you may have a bad accelerator pump or power circuit.
The Fix: Replace accelerator pump or replace carburetor.
2. There may be a vacuum leak.
The Fix: Check and replace vacuum lines as required.
3. The fuel pressure regulator may be operating at too low a pressure.
The Fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)
4. Idle speed set incorrectly.
The Fix: Set idle speed to specs.
5. There may be some type of ignition problem.
The Fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.
6. There may be a fault in the computerized engine control system.
The Fix: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)
7. The EGR valve may be bad.
The Fix: Replace EGR valve.
8. The engine may have mechanical problems.
The Fix: Check compression to determine engine condition.
9. The fuel injectors may be dirty.
The Fix: Clean or replace fuel injectors,