High idle especially during cold weather

[VictoryRed]

normally i idle at like 600ish but sometimes in the cold i get like 1k at idle 5.7 vortec 99 tahoe i do have a tiny vacuum line that is currently taped together could it be that?

 

[GoToGuy]

Fix known problems. In colder temps the idle will be higher as air temp is a factor in engine management.

 

[mattillac]

Info from my 99 5.7 factory tune.

Target idle RPM @ engine coolant temperature:

950 @ 25 F
925 @ 46 F
875 @ 68 F
800 @ 90 F
775 @ 111 F
725 @ 133 F
700 @ 154 F
675 @ 176 F
625 @ 196 F
625 @ 208 F

Food for thought.

 

[someotherguy]

Info from my 99 5.7 factory tune.

Target idle RPM @ engine coolant temperature:

950 @ 25 F
925 @ 46 F
875 @ 68 F
800 @ 90 F
775 @ 111 F
725 @ 133 F
700 @ 154 F
675 @ 176 F
625 @ 196 F
625 @ 208 F

Food for thought.

So in other words,

Measure actual coolant temperature, compare to reading from CTS, replace CTS if needed.

Richard

 

[Keeper]

Make sure your coolant is full also. CTS works best with C

 

[someotherguy]

Make sure your coolant is full also. CTS works best with C

This is true! Much like the sender for the dash temperature gauge, they don't seem very good at measuring air/steam.

Richard

 

[NMNorsse]

In this vein-

In park at full temp in a heated garage my '88 k1500 5.7 idles pretty high. I'd guess 1,200 but I don't have a tach. Put it into drive and it idles around 700-ish, which seems fine. It is the fast idle that I'm not so sure about.

To deal with a variety of issues, including age, in the last year I've replaced PCV, CTS, TPS, O2, EGR, IAC, AIR pump, Intake Gasket, TBI base gasket & fuel line o-rings, pressure regulator diaphragm & spring, fuel pump assembly, fuel filter, plugs, wires, cap, rotor, water pump and hoses. MAP tested good and checked for vacuum leaks with propane and carb cleaner without finding anything. Unplugging the brake booster does make idle go up. I also pulled the ECM fuse for 5 minutes, put it back in, turned everything off, set the brake, put it in park and let it idle for 20 minutes to relearn. It idles smoothly at all times, no stumbles or surges.

Is that fast idle in park at temp the way it ought to be, or am I missing something? It seems too high and I'm out of ideas.

 

[someotherguy]

What temperature is your garage heated to? 195F? If the vehicle sat overnight in a heated garage, at say, 65F - the coolant temp at start time will be near ambient, and idle will be correspondingly high.

Richard

 

[NMNorsse]

What temperature is your garage heated to? 195F? If the vehicle sat overnight in a heated garage, at say, 65F - the coolant temp at start time will be near ambient, and idle will be correspondingly high.

Richard

Thanks for responding here. I started a new thread on this in case anyone has the same problem.

I drove the truck for 15 minutes and then idled it in the 72 f garage for 20 minutes while I was refilling the coolant after the intake gasket change to make sure it was at full operating temp. It went to 210 and then dropped back to 195 and stayed there while I did a 20 minute ECM relearn.