Rough Idle After Replacing 'Spider' Injector or Fuel Pressure Regulator

Rough Idle Was Always Present And What I Replaced Did Not Solve The Issue

If the rough idle problem was there to begin with and whatever you replaced did not solve it, I suggest the following:

1. Check all vacuum hoses are connected and in good condition.
   • Repair or replace as necessary.
2. Check the intake manifold gaskets for vacuum leaks.
   • Spray around the intake manifold, where it contacts the cylinder head, with carb. cleaner with the engine idling.
   • If the intake gaskets are bad and leaking vacuum, the engine's idle will improve (as long as you're hitting the vacuum leak spot).
   • IMPORTANT: This test must be done with a cold engine.
3. Check to see if the intake manifold gaskets are leaking coolant.
   • This is a very common problem with the Spider Fuel Injector equipped V-6 and V-8 engines, since they use plastic intake manifold gaskets (and they are prone to leak).
   • If they're leaking coolant, then they are also leaking vacuum and causing a rough idle condition.
   • You can find out more about this here: Coolant Leaking From Intake Gaskets (GM 4.3L, 5.0L, 5.7L).
4. Do a fuel pressure leak down test.
   • There's a good chance that the fuel pressure regulator or one of the fuel injectors is leaking fuel (and this will cause a major rough idle condition).
   • You can find out (without tearing anything off) by doing a fuel pressure Leak Down Test.
   • You can find this fuel pressure leak down test here: TEST 1: Fuel Pressure Leak Down Test.
5. Perform an Engine Compression Test.
   • You can find the tutorial here: GM Engine Compression Test (GM 4.3L, 5.0L, 5.7L).
   • I have personally diagnosed cases, where the rough idle was due to uneven compression across several cylinders. Unfortunately, the owner had replaced a ton of stuff (and in the process, spent a lot of money) trying to solve it, when the solution was to rebuild the engine (or buy another vehicle).
6. You power-washed the engine, and the rough idle started.
   • You'll need remove and distributor and let everything dry out or blow out the water with compressed air.
   • More than likely the power wash cooled down the spark plugs so fast, that their ceramic insulators broke. You'll need to find them and replace them (if applicable, cause it doesn't happen all of the time after power-washing the engine).
7. The engine needs a tune up.
   • If you haven't replaced the spark plugs, spark plug wires, distributor cap and rotor in like forever, then you need to check these items or schedule their replacement.
   • The cool thing is, is that you can check these items to see if indeed they are causing the rough idle/misfire or not. You can find the tutorial here: How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04) (at: easyautodiagnostics.com).

As you can see, there are several things that can cause a rough idle (misfire condition). Don't let this discourage you, because this is something that you can test/diagnose yourself. You'll need to arm yourself with a bit more knowledge but you can do it. Here's one more resource that may help:

• How To Diagnose Misfire Codes (GM 4.3L, 5.0L, 5.7L).

Where Can I Buy The Parts I Need?

You can buy everything you need at your local auto parts store but if you're like and saving money is on the priority list. Here's the alternative that'll save you a few bucks:

4.3L V-6 intake gasket:

V8 intake gasket: