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Rough idle when cold

Rough idle when cold

Postby derbydriver [OP] » Oct 18 2012, 2:00am

Need a little help. I have a 99 1500 with 5.3L. When first started in cooler weather the engine misfires, runs rough. Then it will rev way up and back down to almost stall and sometimes it will stall and I half to restart the engine. After running for a while and the engine warms up it runs great. I was thinking that the O2 sensor might be bad but not sure. If anyone can help I would greatly appreciate it. Thanks.
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Re: Rough idle when cold

Postby CAMO RAGE 42 » Oct 18 2012, 1:56pm

Hey man you might want to check you'r timimg or timeing sensor or maybe you'r cam sensor.There is alot of things this can be my truck did the same thing,btu this was when i put a new cam in it.It sounds like the same problem thow,my truck would do he same thing.hope this helps you.
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Re: Rough idle when cold

Postby country1911 » Oct 18 2012, 2:49pm

Any codes?
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Re: Rough idle when cold

Postby tankrat » Oct 18 2012, 5:32pm

I'm having a similar problem with mine right now, the more the temps drop off in the mornings, the harder it is to start the first time after sitting overnight. Temps are in the low 60's when I go to work & when I crank it it catches about the same time it normally does but it sounds like it's only firing on about 4 cylinders for the first 10-15 seconds. After that it snaps out of it & runs fine. The only thing I can think of for mine is that it's got a 1-bar MAP in it when it should have a 2-bar & I'm thinking it's throwing off the computer at start-up. Mine has never thrown a code or even had the CEL so much as flash.
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Re: Rough idle when cold

Postby RNGRDVE » Oct 18 2012, 8:36pm

Sounds like a bad intalke plenum gasket. When these gaskets fail they get a crack that lets air in causing a misfire. As the engine warms up the gasket expands allowing it to seal up. On a cold start spray a can of brake clean around the base of the intake plenum and see if the condition changes, if it does replace the gasket.
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Re: Rough idle when cold

Postby masterem88 » Oct 18 2012, 8:48pm

i agree with RNGRDVE. i would check intake gaskets first. it wouldnt be an 02 sensor if cold start problem. your computer does not use 02 sensor input until 02 sensors are at operating temperature.which with yours having heaters in them would take about 2 min minimum. also could be a fuel delivery problem too. when engine is cold it runs rich til it gets to operating temperature. Do you notice hesitation or misfire under hard throttle at all? without scanning for codes or watching sensor data on scanner. its a guess unless you start testing. thats whats hard about trying to answer problems without vehicle in front of you. can only give suggestions or possibilities
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Re: Rough idle when cold

Postby tankrat » Oct 18 2012, 10:16pm

Applicable to mine as well or only to the OP? My plan this weekend was to try to rule out the MAP as the issue & then go from there.
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Re: Rough idle when cold

Postby derbydriver [OP] » Oct 19 2012, 12:45am

There are some codes for O2 sensor malfunction and other emission stuff like bank 1 and 2 running lean. I will check the intake gaskets. Just throws me when it revs way up and then back down. Thanks guys.
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Re: Rough idle when cold

Postby country1911 » Oct 19 2012, 12:47am

Could be a maf sensor with the lean codes. Try unplugging it and see if it improves. If it does, try cleaning to see if that fixes it, if not, replace it.
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Re: Rough idle when cold

Postby RNGRDVE » Oct 19 2012, 12:24pm

tankrat wrote:Applicable to mine as well or only to the OP? My plan this weekend was to try to rule out the MAP as the issue & then go from there.


I was sending more towards the o.p. If your avatar is whats under your hood I have no expreience with blower motors so I couldn't even try to address your concern.
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