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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
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Experience:  Have owned a repair shop for 25 yrs.
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1997 s10: pickup..rough..runs parts and napa wires and it

Customer Question

1997 s10 pickup rough low idle runs fine on the road or engine rpm increase. I have had it to automotive dodge and chevy shops and they can not fix the problem. I keep getting a spark error I replaced the sparkplugs with gm parts and napa wires and it idles much better but still rough. I was told it could be a bad lobe on the cam. What do you think?
Submitted: 7 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 7 years ago.


does the engine light come on?if so,can you give me the computer codes?


Customer: replied 7 years ago.
The error is a spark error I will have to take it back to chevy to get the exact code.
Expert:  Tim's Auto Repair replied 7 years ago.


yes,i would like to have the dont need to take it to the dealer,auto zone and most parts stores will scan it and give you the codes for free,,,,let me know


please ACCEPT my answer so I can get credit for my work.i don't receive commission unless you do ..i'm not always going to be giving you good news,so please dont let this stand in the way of you accepting my does not cost you more money.we will still be able to communicate.. Bonuses and positive feedback are appreciated!if you are not satisfied with my answer,please do not leave bad feed back,i will gladly opt out and let another expert handle the question.PLEASE ASK IF YOU NEED MORE HELP

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Customer: replied 7 years ago.

The error code is PO300


Expert:  Tim's Auto Repair replied 7 years ago.


the problem may be the ignition module...some auto parts stores can test these if you take it off and take it to them.....also,low fuel preswure can cause this...please print and use the charts below to fix this code




Diagnostic Chart
Diagnostic Chart
Diagnostic Chart
Wiring Diagram

System Description
The Powertrain Control Module (PCM) monitors the crankshaft and camshaft position in order to detect if the engine is misfiring. The PCM looks for a quick drop in the crankshaft speed. The PCM executes this test in blocks of 100 camshaft revolution tests. The PCM may take several tests in order to store a DTC and illuminate the Malfunction Indicator Lamp (MIL). Under light misfire conditions, the PCM may also take more than one trip to set a DTC. A severe misfire will flash the MIL, indicating that catalytic converter damage is possible.

Conditions for Setting the DTC


  • Misfire total is greater than 12 counts.
  • Engine speed is between 469 RPM and 6406 RPM.
  • Battery voltage is between 9 volts and 17 volts.
  • Engine Coolant Temperature (ECT) is between 7°C (20°F) and 123°C (254°F).
  • Engine has been running more than 15 seconds.
  • Throttle Position (TP) hasn't changed more than 8% in 1 second.
  • DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0401, P0404, P0405, P0502, P0503, P0601, P0742, P1133, and P1404 not set.

Action Taken When the DTC Sets
The Malfunction Indicator Lamp (MIL) will illuminate if the fault is active within the same conditions for two out of eighty ignition cycles when there is misfire.


The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.


The MIL will illuminate immediately and flash if a misfire is severe enough to cause catalyst damage. The Torque Converter Clutch (TCC) will disable whenever a misfire is being detected with or without a misfire DTC set. (automatic only)

The PCM will record the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. A history DTC is stored.

Conditions for Clearing the MIL/DTC

  • The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed.
  • A history DTC will clear after 40 consecutive warm up cycles without a fault.
  • A scan tool can clear the DTCs.

Diagnostic Aids
An intermittent DTC can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the crankshaft sensor mount hole. Check the porosity and the condition of the reluctor wheel. Whenever the DTC is an intermittent, refer to the Driveability Symptom Tables. See: Testing and Inspection

Perform the fuel Injector Balance Test. Refer to Fuel Injector Balance Test . See: Component Tests and General Diagnostics\Fuel Injector Balance Test Procedure

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. This information on the scan tool can be referred to later.
  1. A visual/physical inspection should include checking the following components:
    • The wiring for proper connections, pinches or cuts.
    • The PCM grounds for being clean and tight.
    • The vacuum hoses for splits, kinks and proper connections as shown on the Vehicle Emission Information label. Check thoroughly for any type of leak or restriction.
    • For air leaks at the throttle body mounting area and intake manifold sealing surfaces.
  1. When all the accumulators are relatively equal, then the misfire is being caused by something that affects the entire engine. When they are not then the misfire is being caused by something that is specific to two or more cylinders.
  2. Whenever the misfire is not present operating the vehicle may be necessary to duplicate the conditions in the Freeze Frame Data in order to detect misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. Whenever the misfire accumulators starts to increment, then misfire is present. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared.
  1. Check fuel for water, alcohol, etc.
  2. A basic engine problem that affects all cylinders is the only possibility at this point. (I.e. cam timing, throttle body leak, restricted air flow etc.) Refer to Engine Mechanical .
  1. Tests the ignition system voltage output using spark tester J 26792.
  2. Replace any spark plugs that are worn, cracked or fouled. Refer to Engine Mechanical if any plugs are fouled or damaged due to an engine mechanical malfunction.
  3. Checks for voltage at the ignition feed circuit.
  1. Whenever the driver circuit is shorted to ground, the light will be ON steady. When the driver circuit is shorted to voltage or open, the light will be OFF.
  2. Since voltage is supplied to the fuel injector on a single circuit, the malfunction could only be a poor connection or open in the fuel injector harness. An open before the harness would result in a Cranks But Will Not Run complaint.
  1. Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCMs must be reprogrammed. Refer to the latest Techline information for programming procedures.
Service and Repair


Ignition Control Module

Removal Procedure


  1. Disconnect the negative battery cable.
  2. Raise the vehicle. Suitably support the vehicle.
  3. Remove the ignition coils from the module.
  4. Remove the module from the assembly plate.

Installation Procedure

  1. Install the module to the assembly plate.
  2. Install the ignition coils. Refer to Ignition Coil.
  3. Lower the vehicle.
  4. Connect the negative battery cable.
Ignition Control Module
icon_note_blank.gif Notes Engine Wiring, RH Side