Background & Context
I have a 2003 Vibe base model equipped with the 1.8L 1ZZ-FE engine, FWD, and the automatic tranny. Odometer currently reads a little over 190,000 miles. My wife and I purchased the Vibe with 91,394 miles back in 2013, and it's been the best vehicle we've ever owned.
For the better part of the last two years, I have been trying to track down the cause of a maddening rough idle that is most notable when the vehicle is stationary and in gear. I'm cursed with a DIY addiction and as a result am pretty comfortable under the hood, so I have been methodically working through an exhaustive list of possible causes as time allows — which I'm afraid is a separate thread for another day.
I had initially considered the ignition coils as a potential cause, but had given them a green light after considering the following:
1) There were/are no pending or confirmed check engine lights or misfire codes visible via my various OBD-II scan tools.
2) Multiple cylinder balance tests performed by disconnecting one injector connector at a time bogged the engine equally across all four cylinders.
3) A visual inspection of each ignition coil for cracks, burn marks, or oil down the spark plug tube wells came up empty.
4) Testing ignition coil resistance with a multimeter revealed no major outliers, with resistance roughly the same across all four coils.
5) Fuel economy was/is still the same as it always has — 30-32 MPG at 55-60 MPG (winter gas), 34-36 MPG at 55-60 MPG (summer gas).
6) Fuel trims were/are somewhat lean, with net STFT + LTFT which climbs to +3-7% at idle but drops to 0% at 2,500 RPM. If one or more coils were weak and causing incomplete combustion, I would expect the ECM to be compensating with a negative fuel trim.
The above body of evidence was enough to initially convince me the coils were not an issue. However, after having since ruled out many other potential causes of a rough idle (dirty air filter, throttle body, IAC valve, PCV valve, or MAF; leaking intake manifold, throttle body, and valve cover gaskets or vacuum lines; worn spark plugs, clogged fuel injectors or clogged VVT-i oil filter; failing VVT-i solenoid, motor mounts, harmonic balancer, or torque converter; low compression, incorrect idle speed, etc.) I am returning my attention to the ignition coils themselves.
Specs Needed for Definitive Ignition Coil Performance Test
This brings me full circle to the reason for this post. Having already performed all basic tests of ignition coil function, I'm now looking to test them definitively to identify any coils which may be failing intermittently, but infrequently enough to avoid setting a misfire code. I believe the two parameters which would enable me to perform such a test would be the following:
— The resistance value between the two outside pins of the 4-pin male connector
— The voltage output of the coil, expressed in kV
Denso's product catalog doesn't specify either of these values for the OEM coil, Denso P/N 673-1300. I did reach out to Denso via email, but have not yet received a response. The Factory Service Manual for the Vibe and its sister Toyota Matrix don't specify these two values either — the coil troubleshooting workflow simply calls for checking resistance between the ECM and coil connectors to rule out an open or short in the wiring loom.
I did check the resistance of all four of my current coils between the two outer pins of each 4-pin connector in search of an outlier. At an ambient temperature of 65° F. (resistance varies with temperature), I obtained the below results by cylinder:
#1 — 22.1K Ohms (22,100 Ohms)
#2 — 24.3K Ohms (24,300 Ohms)
#3 — 22.7K Ohms (22,700 Ohms)
#4 — 23.6K Ohms (23,600 Ohms)
I just purchased the Lisle 20700 COP Spark Tester from Amazon, which should enable me to not only test and view the spark produced from each coil, but also check the voltage output by adjusting the spark plug tester's gap to determine the relative spark strength in each coil. The spark plug tester has a scale marked in kV for exactly this purpose.
While I may be able to use this to compare the spark strength across all four coils, I don't currently know what the spark strength is supposed to be on a new coil for sake of comparison. If anybody has new or new-ish OEM Denso coils and would be willing to test the resistance of the two outer pins of all four coils with a multimeter or the kV voltage output of the coil with an adjustable spark tester, I would be indebted!
Why Not Just Buy New Coils?
I'm not usually a fan of just throwing parts at a problem, and even though my current coils are likely original and now have 190K miles on them, I'm reticent to simply replace all four due to the cost ($200+) as well as the supply chain issues of the last year or two which seem to have reduced the quality of even OEM parts and given rise to many hard-to-spot counterfeits.
I'm pretty fed up with buying replacement parts (even authentic OEM from authorized dealers) and installing them only to find that they work less well than the old, supposedly worn out parts that they replaced. I've had really bad luck with replacement parts the last 2-3 years.
I've considered purchasing a single OEM Denso coil and swapping it into each cylinder one at a time and monitoring the rough idle condition to see if it improves. This would work if my problem is only a single coil, but likely wouldn't if the rough idle is a result of slow degradation across all four existing coils. I could also purchase a single coil and test it for primary resistance as well as kV output to use as a baseline against my existing coils, but thought I'd consult the collective hive mind first to see if anybody has previously tested specs on a new Denso 673-1300 ignition coil.