Extreme negative fuel trims at idle, bogging accel at cruising speeds

1999 Honda Civic EX 1.6L D16Y8 5-MT

Can a stuck open evap purge solenoid (the one on the fuel rail) cause my Short Term numbers to go negative? They are going all the way negative (-30) and only clear up when accelerating hard. Then when I'm in 4th or 5th gear at cruising speeds (40-60mph) it bogs down whenever I want to accelerate a little bit more. It has new fuel injectors, a new fuel regulator, a new distributor and new oxygen sensors. There are no vacuum leaks that I can find and my timing is correct (double checked this past weekend). Any help or suggestions is appreciated before I spend $300 on a oem purge solenoid.

The purge solenoid is normally closed valve. Unplug the electrical connector, to remove any computer control from it and it should be closed. Then remove the hose that goes to the back of the car from the purge valve. If you feel vacuum at the purge solenoid, then it's stuck open. 

It's location top center of engine, not the fuel rail: 




You're right, it's on the fuel rail:
 

 

Ok I'll give this a try tomorrow and report back. Thank you!

Ok so I disconnected the electrical connector and the hose going to the evap canister, and at idle there is some vacuum on it. I left the electrical connector unplugged and put the hose back on and pinched it off. Check the short term fuel trims and they are the same. Could I also have a bad pcv valve?

Stuck open EGR.

The d16y8 doesn't have an EGR valve as far as I know.

What's coolant temperature? What's the running vacuum? Smell the dipstick for fuel. Pull the brake booster hose and make sure the o2 is capable of getting pulled low. What does the o2 volts drop to when you're in decel fuel cut off (injectors shut off during braking). If it doesn't go low, then fuel is some how getting burned. Check your regulator vacuum hose for fuel leakage. I know you replaced it but doesn't hurt to check any way. Check fuel pressure too, there could be a restriction downstream of the return line maybe, so a new regulator won't fix that. Block off the PCV too and see if the trims change.

Pinch the vacuum hose going to the regulator, no need to remove it, and see if trims correct.

For restricted return possibility try disconnecting the return hose on the regulator. That the one that's not connected to the fuel rail or vacuum. Then attach another hose to collect the fuel into a container. Do that before you start the car, lol.

Ok had a chance to change the evap purge valve and it helped with fuel trims a bit but still -20. I was doing some visual inspection and found out the harness for the upstream O2 sensor was redone and im wondering if whoever did it, didn't use a shielded wire for the signal wire. Could that cause problems with inaccurately reading the o2 sensor?

What's your MAP sensor voltage reading at hot idle with no loads on? Less than 1.0V is what we're looking for. Much more, and I'd start to suspect a valve lash issue.

You stated you're looking at -30% trims at idle, but improve under hard accel. What do they read at 2500 RPM in Park, and during normal cruising? Does the upstream O2 switch, or is it stuck rich? Asking because both the rich trims and the bog match a stuck rich O2, causing a false lean condition.

Can you post a photo of the upstream O2 wiring? To answer your question, no, I doubt that a lack of shielding (as in, RF shielding) would cause your symptoms.