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kylebigbucks

What RPM does your 5.7 vortec idle at?

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I have a 98 GMC sierra 5.7 vortec. I am curious as to what other mechanically sound 5.7s idle at becuase I think mine idles to high for some reason. It idles at about 700 when warm. My dads truck idles at about 500 and seems to run a lot better. I would think that all mechanically sound 5.7 vortecs would have the same idle speeds if everything is stock on them...right?

 

Kyle

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Are both trucks automatics?

Idle speed depends on many things. Among them: AC on/off, air temp, engine temp, etc.....

If you consistantly see higher Idle RPMS with your truck under "identical" conditions (this will never really happen, but you know something close), check the IAC (Idle Air Control) valve.

Other things to check for incorrect idle RPM:

Faulty Park/neutral safety switch

Leaky injectors

sticking TPS or throttle blade

faulty battery cables leading to erratic computer compensation

compressor load through AC signal

Malfunctioning MAF sensor

 

Some things to check out there. :jester:

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Mine idles at 700 RPM when warm too! Nothing else running except the motor. 500RPM seems a little low?? :jester:

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I think care needs to be taken here. I always thought the first mark on the tach was zero but I was actually reading the owner's manual (either of a 94 or a 99, can't remember) and it said the first mark on the tachs is 500, not 0. Using this mine idles at about 750 RPM when warm in gear (auto). If the first tach mark is assumed to be zero then it looks more like 500...Bryce

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Fully warmed up, in park, no accessories on= 650 rpm at idle. Truck is 98 Z71 5.7 4L60E all stock. No mention in owners manual that 0 on tach is not 0.

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I just looked at some 95+ dashes and they clearly have a zero as the lowest position on the tach. The 94 and earlier of that body style have 500 as the lowest number.

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I just looked at some 95+ dashes and they clearly have a zero as the lowest position on the tach. The 94 and earlier of that body style have 500 as the lowest number.

:rolleyes: when you turn the key on before you start the engine the needle moves to zero

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when you turn the key on before you start the engine the needle moves to zero

No, mine stays put all the way down when turning to run.

 

94 K1500

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Doesn't the "Emissions" Sticker in the engine bay give specs for that exact engine? Otherwise, the owner's manual will say. :rolleyes:

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when you turn the key on before you start the engine the needle moves to zero

No, mine stays put all the way down when turning to run.

 

94 K1500

Yeah....but yours is a 94, I am talking about 95-98 (00)

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4.3 (3/4 of a 350) idles about 6 here

 

And 992door is right about the tach going to 0 when the key is turned

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500 RPM here. actualy more like 490? Cleaned the throtle body about 3500 miles ago. the gas pedal was sticking. :D:rolleyes::lol:

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