88 civic running rich, stalling at idle, ideas?
 

The car is an '88 DX 4 dr D15B2 5-speed. There is a code 1 (O2 sensor) that shows up only after driving for at least 30 min. on the highway, and if the engine cools it usually takes +30min of driving before it will show again.

Probed the O2 pins on the ECU with a meter while driving, and the O2 sensor voltage appears to fluctuate correctly. Many crossovers 0.3-0.7v and quick response. The only thing that did not pass the troubleshoot from the Helms is when decelerating closed-throttle from +5000rpm, the voltage does not drop low to show fuel cut, it just hovers ~0.8.

Pulled the O2 and bench tested it with a propane torch. All the way to +1.0v with the sensor under the flame, and immediately to 0.1 or 0 when torch is removed. So, reluctantly, the sensor was replaced with another universal Bosch, and no change.

Sometimes when coming off the highway after a long drive and the engine goes down to idle, it will stutter and stall, but start right back up. When this happens, the car is running very rich which is why it is stalling (smell of unburned fuel). Also MPG is down from ~37 mpg to ~30.

The plugs, plug wires, cap, rotor, and timing all check out fine, fuel filter was also replaced.

Unplugging the bottom injector (green one, Honda refers to as auxiliary injector) doesn't seem to help, but unplugging the top injector (brown) does eliminate the rich idle / stalling.

Replaced both injectors with different used ones, no change.

Fuel pump reads ~40 psi when primed with engine off, and ~35 psi at idle with FPR vacuum line connected. Fuel volume measured at FPR return line w/key on for 10 seconds is ~6 oz., Helms spec is 7.8 oz. minimum.

TPS, MAP, and 2-wire ECT sensors all check out within spec with car idling and off, engine cold and hot.

Replaced EACV, ECU, main relay with those from another running D15B2, still no change.

Any ideas?

did you test the compression

compression wouldnt have anything to do with him running rich and stalling at idle..... hmmm thats quite the mystery tho you got me home you get it figured out tho man

check your FPR, the diaphram likes to rip sometimes and leaks fuel through the FPR to the vacuum line, causing the vehicle to run rich, while decelerating, engine vac. is high and will pull more un metered fuel through the FPR

thats what i would start wit gl man

Thanks for the replies. I've tried a different FPR, didn't help. Looking into the possibility of a wiring issue (short, grounds, etc.) currently.