Cars Technical Articles - Rough Idle, Crank No Start, Extended Crank or Misfire Due to Excessive Carbon on Top of Valves or Sticking Valves

Rough Idle, Crank No Start, Extended Crank or Misfire Due to Excessive Carbon on Top of Valves or Sticking Valves

- Edited: Aug 10, 2022
- Popularity: 149 Views



Vehicles Affected:

  • 2000-2020 Buick All Models
  • 2000-2020 Cadillac All Models
  • 2000-2020 Chevrolet All Models
  • 2000-2020 GMC All Models


Some vehicles will have the following conditions:

  • Rough idle
  • Crank no start
  • Extended crank
  • Engine misfire
    One or more of the following DTCs set:
  • P0300
  • P0301
  • P0302
  • P0303
  • P0304
  • P0305
  • P0306
  • P0307
  • P030

  • Cause:

    This condition may be caused by major carbon build-up on the intake and/or exhaust valves due to fuel contamination or incomplete burning of the fuel as shown below, so the misfires should not have appeared until accumulated at least 8,000 km (5,000 mi) or more


  • If there is no sign of valve damage or cam followers that are out of place, perform the following procedure to free up sticking valves and to remove carbon from the valves and pistons.
  • If valve damage is present or if there are cam followers that are out of place, perform engine mechanical repairs as necessary to correct the concern and then perform the procedure below to prevent the concern from returning.
  • Perform an upper engine and valve cleaning procedure.

    Note: Trying a different, high-quality Top Tier fuel and regular oil changes is sometimes the best diagnostic. Additional gasoline retailers are added to the TOP TIER list when their gasoline meets the TOP TIER Detergent Gasoline Standards.

  • Service Procedure:

    1. Fill Cleaner Kit J-35800-A with Top Engine Cleaner, approximately 473 ml (16 oz), and close the cap of the tool tightly. Set the air pressure to 260 kPa (40 psi) at the service tool.

    GM Fuel Injector Cleaner

    2. Using GDS 2 or a Scan Tool, command engine idle to 2000 rpm to prevent the engine from stalling. Typically, 2,000 rpm will be sufficient.
    Note: Two applications of the Top Engine Cleaner may be necessary to perform a total cleanup depending on
    the condition of the combustion chamber.

    3. In a well-ventilated area with the engine at operating temperature, slowly/carefully induce the Top Engine Cleaner into the engine, which should take approximately 3 minutes.
    ⇒ For best results, it is suggested to induce the cleaner through the throttle body with Fuel Injector Cleaner Kit J-35800-A or equivalent and NEW Cleaner Nozzle EN-35800-20, which has been developed to help atomize the

    4. After the entire contents of Top Engine Cleaner has been induced, continue to run the engine for 2
    minutes at idle.

    5. Change the engine oil and filter, and only use one of the Top Tier to minimize future deposits. It can also be recommended to add a bottle of GM Fuel System Treatment Plus at every oil change.

    6. Test drive the vehicle, using only light acceleration, and clear any DTCs if necessary

    GM Valves Carbon Buildup