1999 4.3L 5spd Silverado 160k has been idling a little rough for a while now, when warm, about 600rpm. The SEL is not on.

A few months ago I replaced a failed fuel pump, runs great but didn't improve the rough idle.
Replaced the fuel filter, feels better but still is a bit rough.
Replaced the plugs, a little perkier on the git go, but still rough.
I plan a new dist cap and rotor next.
If that doesn't smooth it out, then a new set of ignition wires would be next.
After that, my hands will be in the air.

A couple three years ago at about 90k, I replaced the factory plugs.
Engine is up to 160k now.
Here is a pic of the ones i pulled last week.
They ran for about 70k miles.
They gapped a bit over 0.60.

They look ok to me and maybe they were even not due for replacement. Their condition suggests that the cyclinders, valves and fuel injectors are all fine.

any comments?

 

First thing out of the box:

replace all tuneup parts with ac delco parts, wires are a little pricey, but worth it in the long run.
at that mileage you may need to do a compression check and be sure all cylinders have even compression, if you have a weak cylinder you will get the rough idle no matter what else you do, but old truck may run for many more miles.

 

A rough idle can also come from a vacum leak around the intake.

 

wellmax - thanks, yep, i tend towards acdelco. i would have thought that if one or two cylinders had problematic compression, then the spark plugs would show it. yes/no ?

RUFFNECK4LYFE - I'm not sure where or how to test for a vacuum leak, can you be a bit more specific? i did replace the lower intake manifold gaskets about 40k ago, which stop the coolant loss. and they are still tight in that sense (still no coolant loss)

thanks

 

Get some starter fluid and spray in short bursts around everything that sucks air, hoses and stuff. If its leaking the idle will jump up. This will help narrow the problem down, if it is.

 

ok. sounds scary to be spraying that stuff. maybe the engine ought to be cold?

 

You could probably use some WD-40.

 

1999 with 160k it's time for a full service, change out all your plugs, wires, cap, rotor, and all your soft vacuum hoses. Next change your radiator hoses and put in new Dex-Cool and a new serpentine belt. Now look at changing the gear oils in you 5 spd. and rear end and you should be good to go.

jvp

 

try cleaning throttle body,if that doesn't help...egr valve is possible cause