1999 Chevy Silverado engine missfire

  • 3 POSTS

Engine Performance problem
1999 Chevy Silverado V8 Four Wheel Drive Automatic 170000 miles

I recently asked a question about my chevy missfiring. You said to clean the injectors I just ran a bottle of injector cleaner through it and it did not help so I took apart the throttle body and cleaned it but it still does it. At first startup it runs good but after 20 minutes of running it starts to miss at idle, or it idles fast at about 1000 rpm.

Do you
have the same problem?
Tuesday, August 5th, 2008 AT 11:43 PM

1 Reply

  • 77,149 POSTS

Check the fuel pressure to rule out the fuel filter, fuel pressure regulator and fuel pump make sure its within specifications-

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.

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Wednesday, August 6th, 2008 AT 3:27 AM

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