99 Silverado C2500 rough idle
 

All,

I bought a 99 3/4 ton Silverado work truck. It's a one owner work truck that I picked for cheap and has about 160k miles on it.

It's not a bad truck,it looks like it's done a few rounds with Joe Frazier but that's OK :)

It's got a vortec engine which seems to have a rough idle. I replaced the plugs which did not help and I squirted carb cleaner around the intake in search for vacuum leaks but it appears that there are none.

It's not throwing any codes.

I'm hoping that I get some insight at what the problem is before I start throwing money at it.

Thanks

Al

Re: 99 Silverado C2500 rough idle
 

You should look for a dead cylinder first and foremost.

Vortec's go through caps and rotors like Hitler through Poland. Unless you know what the complete history of the engine is, you should do a complete and thorough tune up. That includes what I just mentioned as well as wires, ignition coil, fuel filter, PCV valve, and front O2s. Plugs you already did. Spray clean the MAF.

If you look at the coil, you could see tell-tale white spots on the insulation body. These are usually from what I term, side firing to the laminations. One night, check under the hood with the hood bulb pulled out and look for fireworks. The coil is considered a tune up item.

The other thing you want to look at is fuel pressure. Vortecs require about 60 PSI.

The last thing is the spider injectors used in the CSFI system are crap. You cant even clean them.

Re: 99 Silverado C2500 rough idle
 

yeap 99s sucked!! had terrible luck with aftermarket plug wires, only got that miss out with factory dealer pruchased plug wires..

Re: 99 Silverado C2500 rough idle
 

Thanks again. I'm almost certain that it's the intake manifolds as they can leak internally. I seem to also have lost a tiny bit of coolant.

Re: 99 Silverado C2500 rough idle
 

All, I wanted to update everyone on this deal which is now fixed.
I cleaned the throttle body and EGR valve as people suggested that this could be the problem but it wasnt.

The pinging issue was caused by corroded contacts on the cap which was causing the engine to misfire. Once I replaced the cap, the system ran better but still had a rough idle so I went on to replace the rotor and wires.

When I replaced the wires, I realized that the wires on the left side were crossed so I put that right and it began to run great. It still has a slight rough idle but this could be engine mounts or fuel system related. As the truck sat for many months prior to me buying, I'm going to run a few tanks with fuel system cleaner before I take any further action.