Rough Idle After Installing New ‘Spider’ Injector (GM 4.3L, 5.0L, 5.7L)

So, you replaced the fuel pressure regulator, or the entire ‘Spider’ fuel injector assembly and now, when you start the pickup (SUV, van or mini-van) it idles very rough! If this is happening to you, then let me tell you right off the bat that the most likely cause is a major vacuum leak caused by a broken ‘Spider’ assembly O-ring (see photo above).

This is one of the most common problems, encountered after replacing the fuel pressure regulator or the ‘Spider’ fuel injector. So, whether you have replaced the Spider fuel injector assembly (or the fuel pressure regulator) and are experiencing a rough idle that wasn't there before or you're about to take the intake manifold apart, this article will:

  1. Make you aware that the Spider fuel injector O-ring can break and/or slip off causing a major vacuum leak that'll provoke a rough idle condition when you start the engine.
  2. What precautions you can take to avoid this common problem.
  3. And if you're currently experiencing this issue, I'll give you some tips on how to troubleshoot it.

Symptoms Of A Broken ‘Spider’ Assembly O-ring

The most common symptom is a rough idle condition. You could also see one or more of the following:

  1. Loud vacuum leak noise coming from the area around the Spider's electrical connector.
  2. Lean Diagnostic Trouble Codes:
    1. P0171: System too Lean (Bank 1).
    2. P0174: System too Lean (Bank 2).
  3. MAP Sensor Diagnostic Trouble Codes:
    1. P0106: Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem.
    2. P0107: Manifold Absolute Pressure/Barometric Pressure Circuit Low Input.
    3. P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High Input.
  4. Engine stalls.
  5. Bad gas mileage.

Thankfully, there's a pretty simple test you can perform to find out if the Spider assembly O-Ring is the one that's causing the rough idle and/or misfire condition... Let's take a look at the next heading and find out more.

How To Diagnose The Rough Idle Condition Using Carburetor Cleaner Spray

Rough Idle After Installing New ‘Spider’ Injector (GM 4.3L, 5.0L, 5.7L)

As I mentioned at the beginning of this article, the rough idle condition you're experiencing (if you have replaced anything to do with the Spider fuel injector assembly)... is usually due to the rubber O-Ring around the spider's connector breaking, or slipping off, as you installed the plastic plenum and causing a vacuum leak.

Checking to see if this is indeed what's happened in your particular case is pretty easy. All that you have to do, to confirm the vacuum leak, is spray carburetor cleaner spray around the Spider's electrical connector and see if the engine's idle changes.

These are the test steps:

  1. 1

    Start with a cold engine.

    If you've had the engine idling for any length of time, let it cool down. This is important, since you'll be spraying carburetor cleaner spray (which is very flammable) around the upper intake manifold plenum and intake manifold itself and you don't want to risk a fire by spraying on a hot engine.

  2. 2

    Double check that all vacuum hoses are connected to their respective places.

    Checking to make sure you have all vacuum hoses connected will speed up your troubleshooting by eliminating any loose ends.

  3. 3

    Start the engine and lightly spray carburetor cleaner around the Spider Injector Assembly's electrical connector.

    NOTE: The area you're gonna' spray is the one where the orange arrows are pointing to in the photo above.

    If the O-ring broke (or slipped out of its groove) during the plenum's installation... the vacuum that's leaking here will suck the Carb. Cleaner into the intake manifold and you'll see/feel the engine's RPMs stabilize.

Let's take a look at what your test results mean:

CASE 1: The engine's RPMs stabilized when you sprayed carburetor cleaner around the Spider's O-ring area...

...This test result confirms that the O-ring broke or slipped off during the installation of the plastic plenum.

The solution here is to remove the plenum (and replace if necessary the O-ring) and install it again following the suggestion in the next heading: Precautions to Take When Installing the Intake Manifold Plenum.

CASE 2: The engine's RPMs were NOT AFFECTED at all when you sprayed carburetor cleaner around the Spider's O-ring area...

...This test result tells you that the O-ring, around the Spider fuel injector assembly is not broken, nor has it slipped off during the installation of the plenum.

If your vehicle is suffering a rough idle condition (after replacing the spider or fuel pressure regulator), take a look at the section: Spider Fuel Injector Assembly O-ring is Not Leaking Vacuum, What Next?.