Rough Idle when cold

ThirdgenTa

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98 LS1 runs like crap on start up once we dip into these lower temperatures. I just did a tune up on it (Plugs and wires).
It sounds like its missing and surging and sometimes it dies. It does this until the car warms up.
Any idea? Could it be the O2 sensors?
 

ThirdgenTa

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Vac leak?
Wouldn't it do it all the time regardless of temperature? It ran fine all summer on start up but once it got below 45 degrees it did this. It did it last winter too.
 

IZZy

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having the same issue with my XJ, i was told to check the MAF sensor
 

wolfe

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Wouldn't it do it all the time regardless of temperature? It ran fine all summer on start up but once it got below 45 degrees it did this. It did it last winter too.
Oh, I didn't know it did it last winter. I was wondering if it was maybe a small one that when it was warmer out didn't cause that much of an issue and now that it's getting colder it is. Hmmm....
 

blck10th

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If this was a ford thread I'd ask if kurgan tuned it. Rolf!
 

Eagle

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clean the MAF, clean the IAC, reset fuel trims.

what did you gap the plugs to, and what type of plugs did you install?
 

daturbosix

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since cold, my shitbox has like a dead spot at part throttle while leaving a stoplight, sign, ect... if i go WOT im fine...

i think im just gonna spray it, that should clean it up.
 

Turbocharged400sbc

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98 LS1 runs like crap on start up once we dip into these lower temperatures. I just did a tune up on it (Plugs and wires).
It sounds like its missing and surging and sometimes it dies. It does this until the car warms up.
Any idea? Could it be the O2 sensors?
runs like crap in what way surging wise? runs even then starts to surge when in closed loop?
almost like a partial mis? one or multipkle cylinders contributing say 50%?
if surging occurs in closed loop and they are near 50k+ id look at o2sensors soon. typically cold start issues are clogged/streaming injectors that until the fuel rails/fuel and engine get hot the fuel doesnt vaporize well.


since cold, my shitbox has like a dead spot at part throttle while leaving a stoplight, sign, ect... if i go WOT im fine...

i think im just gonna spray it, that should clean it up.
check your tps signal for dropouts esp if its in the same lower sweep of the tps (most of a tps's wear is at the bottom end of the travel)
 

ThirdgenTa

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runs like crap in what way surging wise? runs even then starts to surge when in closed loop?
almost like a partial mis? one or multipkle cylinders contributing say 50%?
if surging occurs in closed loop and they are near 50k+ id look at o2sensors soon. typically cold start issues are clogged/streaming injectors that until the fuel rails/fuel and engine get hot the fuel doesnt vaporize well.

It does it for like the first 5 minutes or so. The rpms will jump all over the place. I think the computer senses that it is about to stall and then corrects it and it jumps way up. Sounds like someone is revving it. And like I said, runs like a champ in the summer and when it starts to get cold it runs like shit.
 

RICH17

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What plugs did you use and at what gap?
 

ThirdgenTa

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What plugs did you use and at what gap?
NGK tr55s I think I gapped them at .55 maybe. Whatever was recommended on LS1tech.
Like I said it did this last year too and with the stock plugs in.
 

RICH17

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iirc I thought stock LSx and truck motors were .040?
 

PANDA

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Does it "run better" if you give it a few more hundred RPM at idle?
 

ThirdgenTa

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Does it "run better" if you give it a few more hundred RPM at idle?

Not really, until it actually warms up.


I tried to get a video of it today. I started it up and I recorded it for about a full minute or so. Then I stopped recording and was about to go inside and it suddenly almost died and the rpms jumped up. Started recording again and it smoothed out.

Here it is with a slightly rough idle but not too bad. I don't think it was cold enough this morning.
http://www.youtube.com/watch?v=/_YvUsL5BPM8
 

Aron

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Start with cleaning the IAC and MAF. I can come over and do it for you if you want/need. Just use a good carb cleaner on the IAC and electronics cleaner on the maf
 

Pewter-Camaro

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Still may be a Vac Leak. Check the hoses around the PCV valve really well. They are known to go bad around there. When its cold it may be allowing a leak but as it heats the rubber softens and Vac will have enough force to pull it shut.
 

ThirdgenTa

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So I cleaned the IAC and the MAF. Gonna wait until it's really cold out to see if it's acting up.

Before

After


MAF
 

Eagle

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:rofl:

Ya, I assume that's going to make a significant difference for ya! :x:
 

Pewter-Camaro

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Yeah all that crap on the screen of the maf will do it. Let me guess.. running a K&N drop in filter? the K&N filter gaskets are way too small and don't seal again the lid so all kinds of crap gets in there.
 

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