rough idle when stopped in Drive and cold weather

[barneytoe]

99 Silverado with 170k miles.

 

Idles just fine when in Park, but when I shift it in to Drive and then come to a stop in traffic or stop light the idle is rough and seems like truck is about to stop.

 

I'm guessing this has something to do with clutch not fully engaging?

 

I should add that the cold weather in Colorado has made this problem appear. I hadn't noticed this issue until the last few days where it's been around 2 degrees out.

 

Thanks,

chris

[Red Clay]

What are your rpms at? Do you have 4wd engaged during this?

 

 

Im in the springs. Are you close by?

[barneytoe]

Didn't notice RPMs but will take a look. Didn't seem to make a difference whether 4x4 was engaged or not, I tried that. Just now at lunch it actually stopped on me while idling at a light so I guess I'm going to have to solve this sooner than I hoped.

 

Another new development is today the "service engine soon" light came on.

 

I'm in Denver.

[oldscsc]

The light coming on is a good thing. Get it scanned and the code should lead you in the right direction as far as troubleshooting the culprit.

[Red Clay]

Go to autozone and have them scan the code.

[barneytoe]

Thanks for the advice, auto store scanned and it came up P0171 and P0174 which is "system too lean bank 1 & 2".

 

RPMs at 500 when at stoplight.

 

I filled up with premium gas today and she's running like a beauty. Also added a can of fuel injector cleaner.

 

So MAYBE it was a combo of cheap gas with ridiculous low temps. Today was a balmy 5 degrees instead of -8.

 

Service engine light has not come back on so I'll just wait and see now.

[txab]

I'd check the fuel filter as well

[mawint]

This may be way off base but check O2 sensors. I was having a rough idle condition once that the upstream O2 sensor on the passenger side went bad and my MPGs tanked.

 

It may eventually set a code but if you put a scanner on it you can see what the last reading was for all O2 sensors. Some scanners can do it real time.

[barneytoe]

Yeah, guy at car shop said same, O2 sensor.

 

If codes come back I think that'll be the next step. Thanks.

[efritz]

You very well could have bad intake gaskets, I know this sounds dumb, but I have seen and fixed it many times, and it always comes up with lean codes too. What happens is when it gets very cold out, they shrink (as they are a bad design to start with), this causes air to leak by and cause the engine to run lean. I would replace your fuel filter too, as it might be the problem and is cheap anyway.

[barneytoe]

Thanks efritz. Fuel filter was replaced around 17k miles ago, and less than 2 years ... so I'm inclined to leave it be. I did hear about intake gaskets as well.

[barneytoe]

This guy had almost exact same issue and solved by replacing intake gasket:

 

http://chevroletforum.com/forum/silverado-fullsize-pick-ups-21/1999-chev-silverado-5-3-code-p0171-p0172-p0420-25872/

 

I'm positive that's the issue here. I'll probably leave it alone until reappears though ;)

[jblakeney]

Sounds like your getting air flow in the engine after the MAF has read the volume of air entering. Leaking intake gasket, cracked intake, or a vacuum leak. Lean both banks go look for where its getting extra unmetered air.

[white1500]

My truck has difficulty with cold starts (sitting overnight), the idling is rough and I need to keep it stable using the throttle for about half a minute.

 

After the 30 seconds or so it will be completely fine and it feels like it finally "wakes up". No rough idling at stop lights or anything once that "sleepy" idle is gone.

 

Not only is this a little annoying because I can't just reach in and start her to warm up while I do something else in the bed or whatnot, but I don't feel comfortable letting anyone else use. I can't stand the thought of someone not knowing what to do when she's idling rough and in need of a little throttle modulation to "wake her up".

[txab]

Have you looked into cleaning the MAF, throttle body, as well as checking for intake leaks?