2002 Silverado rough idle at start up

[Aldon247]

When I first start my 2002 Silverado in the morning, it chatters like a diesel until it warms up. It almost sounds like it's missing a cylinder and knocks a little the colder the temperature is outside. It only lasts 15-30 seconds. Any ideas? Bad plugs or wires?

[diyer2]

Some more info for a good answer.

How was it maintained?

Is the scheduled maintenance up to date?

Check eng. lite on?

Any codes?

How many miles?

What engine?

[Aldon247]

5.3, no engine light or codes, 71350 miles. Very well maintained, bought last February with 60000 miles on it

[Supreme Pizza]

Piston slap.

 

No easy fix

 

No fix needed

[Jsdirt]

Could be intake gasket leak. Classic symptom is it only happens cold, goes away once warmed.

 

Need to see your fuel trims - if they're all positive, then it's an air leak.

[Supreme Pizza]

Could be intake gasket leak. Classic symptom is it only happens cold, goes away once warmed.

 

Need to see your fuel trims - if they're all positive, then it's an air leak.

 

 

You probably already know this, but you can use starting fluid to find intake gasket leaks. It also pinpoints the exact spot of the leak. Spay it around the manifold and of the RPM's go up, you have an intake leak.

 

 

 

[Jsdirt]

Water is even better. Doesn't cost anything, and you'll hear the leak loud and clear.

 

Poke a hole in a soda bottle cap, and you've got a dispenser.

[Supreme Pizza]

Water huh? Never heard of that one. I assume it makes a "sipping" sound if it hits a leak? What I like about the aerosol is that it can get into hard to reach places, like down under tubes & wires. I suppose a smoke machine might work as well in a pinch.

[Jsdirt]

Yeah, it's pretty loud. I've found leaks I never would've found any other way.

 

Flammable stuff evaporates too quick - even worse on a hot engine. Usually with air leak troubleshooting, you want to get at it before there's any heat in the engine, though. Heat usually makes those intake leaks disappear. Still evaporates too fast though.

 

Smoke works too for the bigger leaks. Has to be REALLY calm to find the small ones. Water is quick and easy - no setting up the machine, blocking off intake tubes, etc.. - just squirt and listen.

[Supreme Pizza]

The flammable vapor is what results in the RPM increase. If it did not vaporize, the RPM's would not increase. As we all know, gasoline will not burn. Gasoline vapor mixed with air on the other hand, burns very well.

 

Its interesting that completely different tests can result in the same outcome.

 

1. Water - audible indication
2. Flammable Vapor - Sudden RPM increase
3. Smoke machine - Visual indication

 

Water would be safer for sure. If you use starting fluid, obviously you want to have a fire extinguisher handy, have a cold engine, and make sure no one is smoking.

[diyer2]

Water is even better. Doesn't cost anything, and you'll hear the leak loud and clear.

 

Poke a hole in a soda bottle cap, and you've got a dispenser.

A spray bottle set to stream spray wouldn't work?

[Supreme Pizza]

A spray bottle set to stream spray wouldn't work?

 

[Jsdirt]

A spray bottle set to stream spray wouldn't work?

 

If you're in the field, you use what you've got on hand.

[diyer2]

 

If you're in the field, you use what you've got on hand.

Yep

[Black02Silverado]

Sounds like piston slap, especially since it only lasts a few seconds.

 

The other option is oil filter change. What brand is on it now? Just change it out, no need for an oil change. Go with a Wix or AC Delco and see if that makes a difference.

 

My 2002 tap's pretty loud for the first few seconds after is sits over night and is a cold start up. Once warm it is good to go. No taping sound on start up. Just when it is cold. It has done that pretty much since day one and now has 175k miles on it.