What RPM does your 5.7 vortec idle at?

kylebigbucks · December 10, 2003

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

99-2door · December 10, 2003

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.

Lou'sZ · December 10, 2003

I'm at work now. I'll check my 98 5.7 tonight-will get back with you.

HDChuck01 · December 10, 2003

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

HDChuck01 · December 10, 2003

OOPS! I have a '96 5.7 Liter.

XR Man · December 10, 2003

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

Lou'sZ · December 11, 2003

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.

XR Man · December 11, 2003

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.

99-2door · December 11, 2003

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.

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