2002 Tahoe has a misfire at idle

[JohnnyK]

My 2002 Tahoe misfires at idle. I've replaced everything from plugs, wires,coils, injectors, purge valve and MAP sensor. Nothing has changed. All it's giving me is a. misfire code. It's a inexpensive test but I can't spend a fortune trying to get this thing running

 

[mattbta]

P0300 or P030x where x is a number 1-8?

 

[JohnnyK]

My scanner was only giving me a PO300. I've also done a fuel pressure test on it and when I hit the ignition it's at 58 pounds

 

[mattbta]

So random misfire. Does your scanner have the ability to show counts on each cylinder? If so, is one more than the others by a large margin?

No upgraded camshaft in there?

 

[JohnnyK]

It doesn't have that ability and it has the factory cam in it

 

[rockola1971]

Pop intake snorkel off and with engine running, spray mists of water from a spray bottle into throttle body. Keep doing it without killing the engine for 5-10mins. This will cause any carbon buildup in combustion chamber and piston crowns to dislodge and shoot out the exhaust. Put it all back together, clear codes and see how if misfire comes back. High mileage engines typically have alot of carbon buildup.

 

[JohnnyK]

Pop intake snorkel off and with engine running, spray mists of water from a spray bottle into throttle body. Keep doing it without killing the engine for 5-10mins. This will cause any carbon buildup in combustion chamber and piston crowns to dislodge and shoot out the exhaust. Put it all back together, clear codes and see how if misfire comes back. High mileage engines typically have alot of carbon buildup.

Pop intake snorkel off and with engine running, spray mists of water from a spray bottle into throttle body. Keep doing it without killing the engine for 5-10mins. This will cause any carbon buildup in combustion chamber and piston crowns to dislodge and shoot out the exhaust. Put it all back together, clear codes and see how if misfire comes back. High mileage engines typically have alot of carbon buildup.

The misfire is so bad that it won't stay running after startup. The Tahoe was running great up until I stopped at a red light. Then all of a sudden it died. No signs of any problems. I have to put my foot on the throttle for it to start.

 

[afpj]

If you pull the vacuum line off the fuel pressure regulator, does any gas drip out?

 

[JohnnyK]

No fuel comes out of the vacuum line.. I put my finger over the hole and I can feel a small suction while it is running

 

[Fless]

What's the fuel pressure when you make it run?

When was the throttle body last cleaned, and how does it look now?