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B+ Latch Relay is acting as designed.

Check B+ Latch Relay. Connect DVOM or testlight to D2-5. When KEY is cycled ON should have B+. When KEY is cycled OFF, should hold B+ for a few seconds afterwards. Does fuel pressure drop to 31psi at idle?

Any luck on downloading the Electrical Manual?

Click on your username (upper righthand corner). Click on Account Setting. Under Overview, click on Signature. Add your Year and Engine and anything else about your vehicle. Press Save.

88 Electrical Manual Click on and download the above link. Once downloaded, open file (.pdf). We need to get on the same page.

Yes WOW! What a mess, both under dash and under hood, I hope you live next door to a fire station. Which of the cavities are in use on C236? Your wiring might go 'beyond me and my keyboard'. Also with C235 disconnected, that's trying to tell you something. Follow them wires.

Disconnect C236 at the AC Mode Select Switch (climate control panel) and leave it disconnected. Determine if Blower Fuse still blows. You may have to drive vehicle around for a while, since fuse fails to blow instantly.

Just re-read your first post.

Not going to tell you not to swap out the CTS(ECT) sensor, but if engine was at normal operating temperature, 199° seems like a valid reading. Too bad on no TESTER being around. Would've liked watching FT for awhile. Your STFT reading shows INJ PW (4.6mS) going LEAN. If this is true, suggest the following: Fuel rail pressure could be HIGH. Check vacuum hose from manifold to fuel pressure regulator. Connect fuel pressure gauge. With engine running look for 31psi at idle and 39psi with vacuum hose removed/plugged and engine running. Make sure fuel rail hold pressure for at least 30 minutes (leaky injector(s)).

When O2S heats up (O2 Heater) and starts rapidly switching (RICH/LEAN), ECU should go into CLOSED LOOP. Not sure how TESTER calculates Throttle(%) or TPS(V), could be normal readings, but the TESTER should display only what the ECU sees. You did recheck values with a DVOM? Does the parameter for EXHAUST switch for RICH to LEAN quickly?

STFT (45) shows engine running RICH, engine is in closed loop, so ECU is within its range of authority. That means good. Look into Throttle(%)/Throttle(v), readings seem low. Faulty ECU or faulty TESTER, man tough call there.

It's a 8 slotted grill, if that matters.

Does Blower Fuse (25A) melt regardless of fan speed setting (LO M1 M2 HI)? Blower Fuse also feeds (B+) to the AC Compressor Clutch.

Yeah, suspect radiator temperature switch.

Your very kind, but I can also burn your vehicle to the ground. That what worries me the most.

KEY OFF. Disconnect Radiator Temperature Switch connector. On the harness side (connector), using a fused jumper, connect the two terminals together. Cycle KEY ON. BEWARE, FAN SHOULD COME ON.

YR? ENG?

My reference was for a 4.0L. Sorry, didn't read the fine print.

Difference between 715 and 750 is 35. That's 35 rpm's. That number is calculated and per minute. Divide by 60 to get rps's (per second), like the way your reading it. Now it's not such a big deal.

AC ON or AC OFF, your idle speed should be the same. Your idle is high. My understanding is that 750 will be the target RPM's with engine at normal operating temperature.

That throttle blade adjustment is a calibrated air leak. That setting puts the IAC in its best position for controlling airflow and idle. Do you think the first TPS could've been set to 17% or did you need the extra swing to set it to 17%? Either way, good news.

Values you posted are all good and normal readings. I would now suspect the ECU itself. Let others chime in, maybe I'm missing something.

Need to check powers and grounds to ECU. Your readings seem to be all over the place. Check for voltage (connect one lead at battery negative): D1-5: B+ at all times D2-4: B+ with KEY ON/START/ENGINE RUNNING D1-6: B+ for 2-3 seconds when KEY is turned ON or B+ at all times with ENGINE RUNNING Check for path to ground (connect one lead at battery negative) KEY OFF: D1-3: 0 ohms D2-8: 0 ohms