Bennitoapplebum

Not to complicate things further, but your spark plugs 1&2 are very lean. The +12v power for the INJECTORS are wired from the center. A heavy gauge wire splits into 4, feeding each injector. Meaning 2&4 gets dibs on power. When you plug in your CTS, the ISV reactivates and draws more current. Just something to think about.

You can adjust that all the way down to full continuity (0 ohms). By then, if you can't get the AFR's within a good range, it's safe to say the problem lies elsewhere.

Yes I remember. That is definitely a lean misfire. The next steps would be to: 1. Fully warm engine up. 2. Leave CTS plugged in. Adjust CO pot to obtain a decent idle AFR. 3. Go for a drive and record the driving AFR. 4. Report back with the results of changes. Ex. drive smoother, misfire, kicked ass, blew away a MK5, etc.

No apologies needed, this is all great info for others to read. The resistance readings for the CO pot and air temp sensor sounds reasonable. Pins 9 and 5 would be a combined resistance of the CO pot and air temp sensor together. For the ISV, the 12v is constant(ignition). The ground is a pulse modulated signal from the ECU. The voltage will always vary ~3-12volts, depending on how far off idle target is, engine on or off, etc. You say you had an idle mixture of 15-18. Was it idling decent at all? That doesn’t sound too bad of a mixture at idle.

It can be confusing at first. The sensor reads oxygen 02 content so a higher number means more oxygen (lean). I’m thinking your CO pot adjustment of ~80 ohms might be where you need it. It was giving you a decent idle and driving air/fuel ratio.

Did the idle raise when you plugged in the cts? Or drop? You might have to play more with the bypass screw to find a sweet spot, where the idle doesn’t change much from plugging back in the cts. With the cts plugged in and the engine fully warmed up, record the idle rpm(ECU target rpm). When you unplug the cts, the idle will raise, or drop. Play with the bypass screw in the direction needed to match the recorded target rpm. You need to find a good air/fuel ratio to reach this target. Plugging in the cts will turn on the idle stabilizer back on. And the afr will change a bit, but the idle stabilizer won’t be working too hard to reach the target rpm. If your CO pot is that far off I’m thinking the problem is elsewhere.

Was all this with the CO pot at ~500ohms? Your CTS sensor might be out of range, or your engine may have been still warming up, while unplugging the CTS. By any chance you have the factory thermostat in there?

This type of fuel injection system fires all injectors at once per engine cycle. It requires a slightly richer idle. 13.5-14.5 is probably the leanest it will idle smoothly. Anything leaner will surge and hunt for stability. 14.7 is ideal, but not realistic with this injection system.

Actually your #5 pic (ground bus) is not the correct one. It’s above the fuse box. I can see it in your other picture, after the aftermarket switch picture. It’s bolted right above, has around 10 “fast-on” type connections, with about 4 brown wires occupied. I also see a thin black wire connected to it (looks shaky) kinda burnt. Might wanna check out what that is.

I remember why the CTS needs to be unplugged while adjusting the CO. The ISV idle stabilizer is inactive while the CTS is unplugged. You get the idle speed close to ~800 using the bypass screw. And adjust the CO using a wideband. After the adjustments, you plug the CTS back in and the ISV will hold the idle speed closest to 800rpm with the varying load, power steering, fans, acc, etc. So in your video, your idle was too high. When you plugged your CTS back in, the ISV pulled the engine back to its target idle speed.

Also another thing to point out: The injector flow. I recall you had purchased a new set of injectors. If the flow rate deviates from factory, you may be having to compensate with the CO pot. I’d say wait for the wideband installation to help simplify some things.

Was the car fully warmed up while the CTS was unplugged? You could’ve bee adjusting the CO while the engine was warming up, or cooling down. I don’t know what function unplugging the CTS serves while adjusting CO. I do know that both CO pot and coolant sensors are important for fueling equations within the ECU. I kind of remember unplugging the CTS at one point, for adjusting CO. But eventually ended up leaving everything plugged in while making any adjustments. Does anyone here know why the procedure calls to unplug the coolant sensor?

Shutting down the engine after a drive causes an engine to go into “heat soak” mode. The entire engine heats up due to the cylinder’s heat not being transferred to the radiator, fuel cooling, etc. When you restart the car during this stage the ECU delivers an increased ASE(after start enrichment) for a period of time~30 sec. Judging from the symptoms you explain and from the color of your plugs, your issue seems to be fuel related. Any ignition system will have a hard time lighting a mixture as lean as yours, especially during increased load. A quick test would be to crank that CO pot up by a large amount and see if she drives better or worse. I’m betting it will run way smoother and consistent.

Would you say that your engine has reached a higher temperature while sitting? If so, then heat related intermittent problems are, guess what... ground related. When metal expands under heat it sometimes increases the current capacity in poor grounds. This may not be your case. Just something to think about.

Yes you can tune the idle that way, the mixture and idle speed go hand in hand so constant back and forth adjustment might be required. Yes getting a wideband will definitely help with tuning and diagnostics.