Rough Idle

[ace903a]

Hi;

I have a 1999 z71 4x4 5.3 and in very cold weather (-20c) the check engine light comes on and it idles very rough. Engine rpms surge badly. The truck seems to run ok at speed, but idles badly. This seems to clear up when the weather warms up.

Any ideas, could it be an o2 sensor problem?

[facn8me]

Several things it could be. Having the code would be the most help. Most everything else is guessing. Try a couple of local part stores and see if they can read the code the let us know.

[ace903a]

Thx.....I'll try to get the codes and get back

[bigredexpress99]

Yeah I have the same problem. Same truck actually, 99 Z71 5.3. the code I get is a misfire on cyl 5. I have replaced all spark plugs (NGK TR55) , checked all wires, they are all within spec (if it aint broke dont fix it), The injector is pulsingand getting a signal. I have swapped out the coil with another buddy's and it still did it. Maybe its a 99 pcm problem or something? Kinda like the false knock.

[budhayes3]

Still could have an injector problem...even though it's pulsing, it may be partially clogged or have a poor spray pattern. I've seen injectors break the pintle off and still "appear" to be working...the electrical part still does it's job, while the mechanical portion is rendered inop.

 

But yea, first thing you need to do is get a code.

[Shaners]

A good "top-end" cleaner like Sea Foam may cure the problem. You may also want to check the throttle Body for dirt and carbon build-up and clean it too...