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autotech2612

Idle Quality - Low To High When During Cold Temperatures

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I do appreciate your help thus far, and I have expressly thanked you many times. I don't know why, however, you express such a poor attitude. I asked logical questions in my previous post, but your response isn't mature.

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Temperature is not low enough to warrant blocking the radiator. Even at sub zero temps - after a few minutes of cruising, engine should get up to temp pretty quickly.

 

The way it is cooling down when the engine is not loaded, but gets up to temp just fine after some cruising. That almost sounds like s cooling system issue. The ETC sensor could have been a red herring the whole time. Even brand new thermostats can go bad. Could even to a worse problem, like a blown head gasket or damage to the water jacket, cooling system.

 

Best thing to do to nip this in the butt. See if you can get your hands on an auxiliary temperature sending unit - something complete independent of the car's system. The OEM temperature sending unit doesn't have the best resolution or response - so it can be tough to pickup the transient temperature swings that can point you in the right direction.

 

I won't completely rule out any electrical gremlins. From how you described the issues - sounds like this one will be tough to pin down. You need to add a independent control point, ground or absolute truth sensor to see what is really going on.

 

In the meantime, as long as you haven't noticed any issues with driveability, heat from the heater core, and MPG seems to be consistent - just drive the car.

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Thanks, fish.

 

How do I go about installing an auxiliary temp. sending unit? And where do I find one?

 

Today it did the same thing with 35 degree temperatures. After a 14 minute highway drive, I was at a stop light and the needle went down a little.

 

This behavior was evident even before the thermostat was replaced.

 

What about a water pump? And, would a clogged heater core have anything to do with this?

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Any aftermarket one will do - them make ones that tap into the into the same place the OEM sending unit plugs in. Some run inline with a radiator hose. In any case - need to find a baseline for the coolant temperature - see if it is really fluctuating as much as the OEM temp sensor is saying it is.

 

I've seen them on JEGS, Summit Racing, other online retailers (Amazon, etc.). Some trailer hitch companies might also have links to them. At retail stores - probably hit or miss, if they do have a SKU for that item, they might have to order that in. At the very least - a different gauge to the sending unit you have. As the OEM cluster gauge doesn't have a very high resolution. I've even used a K-type TC probe from my multimeter - wired it into a bung, sealed it - then attached it to a t-fitting, coming off the original port that goes the OEM ECT sensor.

 

A bad water pump (cavitation damage) could explain some of what you are seeing. Sludge in the heater core, inside some of the water jacket or bottom of radiator is another possibility. Heater hoses (suction side) that collapse internally can also be a potential issue. Sometimes the hoses can visually look fine, but be ripped up internally. An auxillary temp monitor will let you know.

 

No sense jumping to conclusions, swapping parts until you verify that the temperatures are good. If it is - then that points to a bad ECT sending unit, as the ECM uses that to control idle speeds, etc. If the temperature of the coolant really is all over the map - then you can focus on the cooling system. Look for signs of corrosion, sludge in the radiator - check the integrity of the hoses, then look into the possibility of swapping the water pump.

 

I'd throw in a compression test and UOA - just for good measure, as these are low cost compared to swapping parts out. This will rule out anything catastrophic internal to the engine. Depending on the outcome of these two quick tests - tells you that the engine is good to go or to stop and reassess the situation.

Edited by fishexpo101

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Another update:

 

Still no cardboard in front of the radiator. 18 degrees tonight (coldest so far this winter). Took a seven minute trip on cold engine. Arrived at destination, and needle moved an inch, but I had decent heat

 

an hour later, 18 out, I drove seven minutes home. Was throwing out good heat, but needle was only 1.5 inches from the bottom.

 

a friend had stated maybe the temp. gauge is correct, but the heat was really good to the point that I don't think I have any radiator obstructions or water pump issues.

 

Will be changing back to the SMP sensor tomorrow to see what changes as our temperatures are going to range from 22 during the day to 15 at night until Friday.

 

Also filled up two nights ago and my fuel economy registered at 34 miles per gallon, so I don't think this issue is really affecting my gas mileage. Due to the cold, this is about normal. However, tonight, even though the car was throwing out good heat, the idle was at 1200 - 1250 because it thought the car was needle was low, thus, car thought it wasn't fully warmed yet.

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Yeah, sounds like you have good heat and the car is warming up like it should. Gauge and/or sending unit is still suspect in my mind - even in subzero weather - my 2002 always came up to temp and stayed there, no grille block needed.

 

Could be the thermostat is opening too soon or not rated at the temperature that it is stamped. As your symptoms sounds like running a cooler t-stat.

 

Can't eliminate an ECM issue or wiring issue - but those can be a nightmare to track down, even with a multimeter on hand.

 

Sounds like a plan - changed out to the better SMP sensor. I'd just drive around and bit, see what it does. Noting fuel economy and what your idle speeds are doing. Unfortunately, once it closed loop mode, the ECM will rely on the ECT temperature measurement - if it is reading too low, your fuel economy will suffer as the engine will be set to fast idle and (automatic) transaxles set to not go into overdrive/higher gears.

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Another update

 

We have lows of 7 right now. I swapped out the ECT sensors before heading out and now have the aftermarket installed. I went for a 15-minute drive consisting of 75-percent highway (50-55 mph) and the rest city. The gauge moves quicker than the OEM. Arrived at destination and I was at the half-point, but idling at 950.

 

Car sat 40 minutes.

 

Re-started and drove back home. In garage, car idled at 800. Turned off. Sat for three hours. Outside temperature didn't change. Left for a another highway drive (50-55mph) with I'd say 85-percent highway and the rest city. Arrived at destination. Had hot heat and gauge was at halfway point, idling at 950.

 

Car sat for 45 minutes. Drove back home in same 85/15 percentage above. Heat was very hot and when I arrived home, car was idling at normal 800.

 

Note, I did flush the heater core twice in November. There is no cover on my radiator. Last year my heat was never hot -- just warm to very warm with cover on my radiator.

 

Temps will remain this way until Friday, with a low of zero Wednesday night.

 

Based on this performance, I have to agree it's an electrical issue. Also, with the aftermarket ECT sensor re-installed, the needle on the gauge is not going lower when idling like with the OEM.

 

Will upload visual images starting later today of outside temp and idle, while manually reporting miles and minutes.

Edited by autotech2612

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Okay, I like visuals. Photo one is taken after a 7 minute city drive, speeds up to 35 in fifth. Car sat for 18 hours before taking off. Right upon parking, I snapped the photo. Heat is actually decent (warm, not lukewarm). I'd say this is about normal -- if not better.

 

002_zps1fa19ecd.jpg

 

 

Car sat for one hour and ten minutes. Upon starting and idling for a few seconds, this is what it looks like:

 

004_zps910d2be0.jpg

 

 

 

Drove 7 minutes home, same speeds and some coasting. This time, I noticed the needle starts falling when I'm coasting to the stoplight. Heat is just lukewarm. Upon pulling into the garage, I snapped this final photo.

 

005_zps3169a635.jpg

 

 

Ever since I replaced the intake manifold, my CEL has disappeared (no, bulb is not burnt out). Odd, since I had EVAP codes as you know.

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That needle moves around way too fast. Even mine doesn't really move that much until it starts to get in its operating range.

 

It was 7 degrees this morning for me - mine warmed up fairly normally. That fact that the temp drops when coasting (low load) and goes back up when under load - makes it sound like a bad t-stat or even a blown headgasket. Really need to put an independent temp gauge on there and see if the coolant really does heat-up / cool-down that quickly.

 

There is a possibility that this is electrical - but when you mentioned that when the temp gauge is low - the heat output is lukewarm - that doesn't sound electrical to me.

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^^^ I'll do my best to get you some specs tonight to help you buzz the sensor out.

 

There is a remote possibility that the wire is broken inside the jacket - every time you mess with the sensor and move the wire around - it will read different each time.

 

This is pretty common on some older GM cars - wire would be resting on the valvecover or touch the EGR - intermittently short out. Like in your case - once you know the engine is warmed up - heat output from HVAC system is good, car seems to run normally otherwise.

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