Cold idle issue

[rickbert]

94 Suburban 5.7 220k miles.....

New issue....

Let me say my Burb runs absolutely perfect in every way...idles great, perfect acceleration, no hesitations, starts and shuts off without a hitch....

EXCEPT when it's been sitting all night and it's colder outside.

When it's colder and it's been sitting overnight it will start right up perfectly but it will idle horribly. Sputtering, shuttering, VERY noxious smell from the exhaust....tach up and down a tad....

THEN after about 20-30 seconds it smooths out and is PERFECT the rest of the time. If I stop somewhere for a bit then restart it it's just fine in the cold...

This only happens when it's colder and has sat overnight.....the other morning I went out and it was in the upper 40's and raining (so very humid) and it started and idled fine without the hesitation after sitting all night. One afternoon after sitting all weekend it was almost 60 degrees and it didn't do this.

It's like it has something to do with something that senses temperature ??

Kind of like an old carb engine and you un-choke it too soon.

Again the keys to the mystery: ONLY when it's BOTH cold outside AND the engine is cold and it only lasts about 20 seconds.

Your thoughts..

 

[zora]

bad engine temperature sensor or the wire harness connected to it.

 

[rickbert]

Now that you mention that.....

I had the intake gaskets changed about a month ago and when the shop did that they said they had to put a new engine coolant temp sensor in because when they pulled the original off the wiring was so brittle that it just broke off.

AND this issue didn't start until AFTER they did all that....so possibly as with the cheap after market EGR valve I mentioned I put in another thread that didn't work right (I replaced it with OEM and it then worked perfect) perhaps maybe they put in a bad one ?

I will give that a try...looks simple enough to do myself as well.

EDIT....I just watched a video on how to do this....and it showed draining the radiator first ? This sensor is at the top of the engine so WHY do you need to drain the coolant ? When watching that video I saw NO apparent reason why ? It's not like if the engine is cool that coolant is gonna come gushing out of there right ?

 

[zora]

if you are sure the sensor is higher than anything else in the cooling system you will be OK. If you do have to drain it probably does not have to be completely emptied.

 

[rickbert]

Pic I stole elsewhere online.....just like mine, right on top next to the thermostat housing....

And I believe THIS is the part you are referring to:

 

[zora]

It is below the hose so some fluid will come out, you can try a quick two handed swap of old and new but probably be best to just lower the coolant level.

 

[rickbert]

Yes you are right.....I've changed the thermostat a few times in the many years I've owned it and a "little" comes out of that hose and the thermostat opening but not enough to worry about....so I imagine even less will come out of that little opening than the thermostat opening and even less seeing how I don't have to undo that hose as with the thermostat. One thing I have a lot of in my garage is old towels.....I'll just lay a few around the area to soak up whatever comes out.

BTW THANK YOU for your advice every time ZORA....I'll post the results whenever I do this in a few days.

 

[rickbert]

Ok....6 months later....I just yesterday swapped out the coolant temp sensor as the weather started heating up right around my last post to this thread and I didn't have the issue all summer. The weather has now cooled so I swapped it out yesterday.

This morning I went out to start it (35 degrees) and still same issue....rough idle for about 30 seconds then runs absolutely perfect...just like when I started this thread.

I've since read that that part only sends a signal to the temp gauge on the dash which is it's only function and does not communicate with the computer....so replacing it didn't help.

Any other ideas ??? Thanks

 

[zora]

there has to be a temperature sensor that communicates with the computer, it is not unusual to have two, one for each function. Look at this NAPA listing, they have a sensor for the gauge/light and a second one for the PCM. Did the sensor you replaced at the thermostat housing have two wires? Do you see a second sensor on one of the cylinders heads with a single wire? Did you test the top sensor with two wire harness with a test light or voltmeter to determine if either wire is hot? If you unplug the single wire sensor does your temperature gauge read zero?
https://www.napaonline.com/en/searc...cation=true&indices=API&referer=nol-veh-conds

 

[rickbert]

The first pic is the one I changed....on top right by the thermostat housing...it has 2 wires and I DID notice it changed my temp gauge by a few degrees when I swapped it out the other day as my temp gauge reads a few degrees hotter before the thermostat opens and it goes back down...so that one does AT LEAST control the gauge on the dash.

The second pic is on the right side of the engine right below the valve cover as you see...looks very similar but only has one wire to it. Is THAT possibly the other one you speak of and what I should have changed ?

 

[zora]

yes that is the other sensor. The strange thing most of the write ups I have seen state the two wire sensor on top is for the computer but based on your results it appears to be hooked to the temperature gauge. You can confirm that by disconnecting it and see if the gauge stays at zero. If that is confirmed then the single wire sensor on the head is for the computer and should be changed.

 

[rickbert]

PROBLEM SOLVED....3 YEARS LATER !

Believe it or not this issue was solved by installing a GENUINE GM A/C DELCO distributor cap. I had swapped the cap out 2 other times and even with a brand new (aftermarket) cap I had the same problem. Last week I installed an A/C DELCO cap and this issue is no longer.

Couple years ago when I had a a bad EGR valve I replaced it with an aftermarket EGR valve and it idled right, no more check engine light but it would hesitate slightly when accelerating after coming to a stop so I took that back and spent twice as much on an A/C Delco EGR valve and THAT problem was totally solved.

SO twice now I've learned my lesson.....DON'T BUY AFTERMARKET PARTS....at least not electrical parts or parts that are sensored by your vehicles computer.

After installing this new cap my 27 year old Suburban runs like freaking brand new....smooth quiet and perfect idle from the get go.

It wasn't that the cap I had on there was bad.....it just wasn't genuine GM. AMAZING

 

[zora]

Do you recall if the metal contacts in the aftermarket cap were different from the Delco cap?
I can only guess you had condensation in the cap and had spark scatter in the aftermarket cap while the Delco cap due to different materials or design was resistant to.
Thanks for the update.

 

[rickbert]

Do you recall if the metal contacts in the aftermarket cap were different from the Delco cap?
I can only guess you had condensation in the cap and had spark scatter in the aftermarket cap while the Delco cap due to different materials or design was resistant to.
Thanks for the update.

Well, AS SOON AS I would install that aftermarket cap and start the truck it would have the crappy idle ....so I'd say (not to be argumentative) it didn't have time to gather condensation that fast when it was brand new. So I don't know !

 

[zora]

Well, AS SOON AS I would install that aftermarket cap and start the truck it would have the crappy idle ....so I'd say (not to be argumentative) it didn't have time to gather condensation that fast when it was brand new. So I don't know !

Ok, based the condensation on your first post.
Any chance the aftermarket cap was made in China?

 

[rickbert]

Ok, based the condensation on your first post.
Any chance the aftermarket cap was made in China?

I wouldn't know....but I'd not be shocked if it was.