The engine seems to start fine and will normally accelerate fine. As you are driving and maintaining a steady speed, the engine seems to "speed up" slightly or it seems to miss and buck.
If you have a carburetor (there are still a few out there), the choke may not be set properly, or the choke may not be working correctly.
The fix: Check the choke plate and make sure it is opening completely.
The engine may be running too hot.
The fix: Check and repair cooling system.
The fuel pressure regulator may be operating at low pressure.
The fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)
The ignition timing may be set wrong.
The fix: Adjust ignition timing.
Ignition system problem.
The fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.
- There may be a fault in the computerized engine control system: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)
The fuel filter may be partially clogged.
The fix: Replace the fuel filter.
Torque converter (automatic transmission only) may not be locking at the right time, or it may be slipping.
The fix: Check lock up circuit or replace torque converter. (Not a DIY job)
There may be a vacuum leak.
The fix: Check and replace vacuum lines as required.
Possible internal engine problems.
The fix: Check compression to determine engine condition.
EGR valve may be stuck open.
The fix: Replace EGR valve.
Drive axles may be loose or worn.
The fix: Check and replace CV/universal joints as required.
The fuel injectors may be dirty.
The fix: Clean or replace fuel injectors.