Hi, Nudge_uk and the usual suspects are:
1. Spark plugs in bad condition or partially fouled.
2. Spark plug cables in bad condition and leaking check for spark leakage in the dark.
3. Spark plug gap too close or too wide.
4. Faulty ignition coil, module, and or sensor.
5. Battery nearly discharged.
6. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
7. Intermittent short circuit due to damaged wire insulation.
8. Intake air leak.
9. Water, dirt, or rust in the fuel system, fuel pump and/or filter.
10. Old dead or bad fuel.
11. Faulty fuel pressure regulator
12. Pinholes in the in tank plastic convoluted tubing from the pressure regulator to the quick disconnect check valve.
13. Fuel tank vent system plugged.
14. Throttle body controls misadjusted.
15. Damaged throttle body or intake seals.
16. Loose, dirty, or corroded ignition module connector at crankcase.
17. Faulty TPS, MAP, CKP, O2, and/or CMP sensors.
18. Incorrect valve timing.
19. Weak or broken valve springs.
20. Damaged intake or exhaust valve'
21. Control module may be in "LIMP" mode
22. Check for engine trouble codes.
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