Ωhm

Try swapping both O2 sensors. Make sure problem doesn't follow the sensor. Maybe make jumper wires, PRE to POST and visa versa.

One more thing, that hose clamp looks like it missed it mark. Needs to move up the hose, could cause problems later down the road somewhere.

That vacuum cap has cracks in it. Could be a vacuum leak.

What's your ST & LT Fuel Trim values? Looks like your running LEAN. Check your manifold bolts.

Maybe post a photo of your radio. @Minuit Any insight here. ↑↑↑

Michigan offers both Historical Vehicle Plates and Authentic License Plates. Authentic Plates are plates that are era correct for the vehicle (@Chad R has one). To qualify for a historical or authentic license plate, vehicle must be: • 26 or more years old — based on vehicle model year subtracted from current calendar year • Owned solely as a collector's item • Used only for events such as historical club activities, parades, and car shows. Note: A vehicle registered with a historical plate or authentic historic plate cannot be used for routine transportation, except during the month of August when it may be driven anywhere in the state without restrictions.

Yes Yes. C355. Color coding matches schematic. Don't know why the other end of C115 is missing or can't be found, but the only wire needed is (BLK/YEL) for backup lamps. Other two wires are for AUTO's.

Must not be equipped with Headlamp Delay. C115_H Backup Lamps C115_J&K Auto Trans stuff. Looks like I see a Clutch Pedal. All three (3) circuits use the TRANS fuse (7.5A).

Yes. Pull the connector.

Two fuses, three components. Wiring diagrams can be most confusing, especially when they try to cover all types/combinations of all the parts on a one-page schematic. Try disconnecting, one at a time, in any order, the following: Radio Clock Headlight Delay Module See if this will tell us anything.

Can you setup your meter (draw test) for the Fuse Link (H) again, but this time pull fuses out? Start with ETR, HD LP/DLY. Make sure you're not running any accessory's off of the B+tap next to them. Maybe this can help narrow down faulty circuit and put a name on it. That one single connector wire (photo) is for your Engine Compartment Lamp, if equipped.

Check your Glove Box Lamp switch, if equipped.

IDK. Anyone else.

1988 is used for 89 & 90. Best I got. _mj1988electricalmanual_1.pdf

Check and make sure the TPS wiper arm, is on the correct side of the throttle plate wiper. Sound like it's on the wrong side (0.17vdc).

MJ_1987_Electrical_Manual_1.pdf

Check for proper adjustment on your Brake Lamp Switch.

Just as a quick check look for fuel at the vacuum hose between the Fuel Pressure Regulator (FPR) and intake manifold. Leaky FPR. @brucecooner

Could be just the photo, but hose looks too long, needs trimming. Could be pinched or kinked. Aeration.

If you just “do it”, then you can forget all about it. Hope this helps.

On the end of the fuel rail. @brucecooner With ENGINE at IDLE, vacuum hose connect, look for ≈31psi, with hose disconnected, look for ≈39psi.

Stay positive especially when you want all your test results to be negative.

Tape up that Splice and it sounds like your good to go with those wires.