it happens all the time. it started as just studdering randomly once in a while, and sometimes the tach would die randomly too. it progressively got worse and worse. at first it would die, then start right back up, the i'd have to wait 5 minutes to restart it, now i have to wait 10+ to restart it. it does it all the time, temperature doesnt matter. it's done it when it 90*, it also does it when it's well below freezing.
I presume you are talking about the temperature of the weather outdoors not the temperature of the lower engine block. This is important, because your engine temperature gauge only tells you what the temperature of the coolant is at the transmission side of the upper engine block (where the coolant exit hose is), not the temperature of the lower crankcase or the much hotter temperature of the cylinder heads. (heat rises)
Due to the tach readings I would strongly suspect that the tiny magnet of your "CPS" Crankcase Position Sensor is fouled and malfunctioning.
The CPS is a transistor Hall Effect magnetic sensor on/behind the large lower pulley on the bottom left side (passenger front wheel) of the engine. It can be replaced but you need a special puller to yank the pulley off (through the passenger wheel well) the crankshaft to get at it.
Unfortunately, what happens, over time (mileage like 180k) to these otherwise very reliable electronic solid state "timing points" replacements (that also provide the rpm tach signal) is that the magnet in it attracts metal filings from the brake discs. In other words, there is nothing wrong with the sensor it just looses sensitivity because small metal brake rotor filings (steel dust) somehow gets sucked into it and sticks to it's exciter magnet, enlarging and miss shaping the magnetic field that the slots in the pulley vanes are supposed to open/block for timing/rpm/index signals. It's not just from your own rotors, big trucks and other cars in front of you also stir up road dust containing metal filings that end up in your engine compartment.
The small tip of this sensor has a permanent magnet on a post between two transistors like so:
Sensor| gap |Magnet| gap |Sensor
The back of the main crankshaft (indexed by a slot-key) steel pulley has two cylindrical sets of notched-metal vanes, one that registers a full rotation (one notch for RPM that is also the fire order index point) and the others that register the six TDC cylinder/crank position timings (six notches for sequential timings). Without this sensor's two signals the tach and/or ECM/sparks cannot function, and a limp (lost tach-index count reference) will eventually lead to a backfire.
What happens to the sensor is these foreign metal filings (shown here as
>==<) get stuck to the magnet, progressively and randomly fouling, weakening the (apparent) strength of the modestly strong tiny embedded-in-plastic (alnico?) magnet and corrupting the (apparent) size of the magnetic gap like so:
_ _ _ _ _ _
>>======<<
Sensor| gap>|Magnet|<gap |Sensor
_ _ _ _ _ _
>>======<<
Like anything electronic, the Hall Effect Transistors lose sensitivity as they get warmer so once the lower engine block warms up a bit (especially in city driving or at a stop/light where there's suddenly way less cooling air flow at the bottom of the engine) they no longer produce a strong enough signal and the system suddenly fails. More importantly the 6X timing signals can become inaccurate/erratic causing rough engine run, degraded fuel economy and higher pollution. The engine computer, thus being fooled by these erratic (chronically delayed and/or erratic) mis-timing signals will falsely (and consistently) assume that these rotational timing aberrations are happening because your coils (or wires or plugs) are at fault. Depending how big a metal filing is on what side of the magnet it can affect either the just the tach or just the ignition system firings or both.
So basically you have to replace a perfectly good sensor, simply because it's center magnet is covered with steel (iron) brake rotor filings, there is really nothing else actually wrong with it. When you remove it and examine it closely you will clearly see these small steel brake rotor filings all built-up on it's center-pole "exciter' magnet. Larger filings are an even bigger problem, and time/mileage on the road need not be a factor if you have recently done the front brakes.
If you either replace it with a new, unfouled one or just use a more powerful magnet to remove the filings in/from it (and put it back in) all will be well again, save it will inevitably happen again, especially if you are a big (city driving) brake user or upgrade to metallic pads.
The permanent cure for this is to obtain several EXTREMELY powerful flat quarter-arc
Samarium Cobalt or Neodymium (NdFeB) Magnets from an old computer hard disk drive head-arm actuator (thus totally destroying it before you throw it out, they all have two of them inside) and stick them (three or four of them) to the engine block close as possible to/around the base-back air space-slot of/behind the crankshaft pulley!
These incredibly powerful Neodymium or Samarium Cobalt hard disk arm-motor permanent magnets will quickly and easily capture almost all of the brake rotor dust from the dusty road-air around the area of the block behind the pulley, preventing air turbulence created by the spinning crankshaft pulley vanes from inducting metal filings along with other harmless dirt and dust into the engine's all-important CPS sensor forevermore.
GM provides a cheap plastic "foreign object guard" on the engine block around the back of the pulley to minimize air flow back there but it has no effect on brake (and bumper to bumper metallic rush hour road) dust, you need powerful magnetic "traps" to capture this sort of dusty-metal air-turbulence pollution before it ever gets close enough to the pulley gap to get sucked-in there. This will hopefully be the last of your engine's annoying CPS sensor problems, for a long long time.
TIP: Similar single-element Hall sensors are also used (one each) on the two front axles behind the brake rotors to provide the TCS/ABS control with front wheel RPM detection, and must likewise be cleaned of filings/rotor dust regularly during brake or front end bearing axle repairs or the TCS/ABS will similarly, eventually also appear to fail or go intermittent.
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