First road test in a while went horribly wrong....

Hello members. Unfortunately, my road test late last night went awful. To make a short simple forum post, here are the symptoms. Any input is much appreciated. This is a 95' 240sx SR20DET on a Haltech 1500 (I will include my diagnosis up to this point after all the symptoms)

Initial idle went great no problem getting up to op temp

0 Cruising in neighborhood, my idle would drop to about 600 (normal is 1000), correct itself, and idle like normal again.

During road driving, car acted fine for 10 mins, then went crazy. Any more than a hair on the throttle, and the car would spaz out, (missfire, buck, almost like a launch control but in all the wrong ways)

Put it in neutral during a turn, car fell on its face, and could not correct for the super low idle. Died, and would not fire back up. Crank, but no fire.

So far, I have done a Leakdown test, fuel pressure test, and checked my plugs. No signs of failure except a very white plug on cyl 4.

Please, any help would be appreciated, and I would be more than happy to give any information I can. Im also open to video calls or whatever else to help get this car home. Thank you everyone.

Parker,

If one cylinder looks very white compared to the others, I would check items specific to that cylinder. You've tested the engine, so I'd look for intake or exhaust leaks at manifold, gaskets, etc.

Perhaps the coil has an issue.

Is the plug porcelain cracked?

Are the injectors known good?

As Mike said, if one spark plug is different, that strongly suggests it needs investigation.

But that would be expected to drop the cylinder, and not produce the symptoms you suggest - except a misfire will mean that cylinder's air is going to be passed through the exhaust and be registered as a very lean condition by the lambda. Depending on the way your ECU is set up, there's a good chance the ECU is going full-rich to try and compensate for this, and this will cause the engine to run very poorly.

What were the other sparkplugs like?

Hello Gord and Mike, Unfortunately I have been at it all week after work. I have data logged a drive, and have plenty of run time. It seems to be fine except a couple persistent issues.

The car drops lower than I would like when pushing in the clutch. 690-740, then raises back up to a stable ish 1000-1040 idle. Weird.

Another issue that occurs is a solid missfire at higher rpms when held at 3k or 4k.

Would anyone be able to look over my logs or seen anything like this before? Thank you all for the help. It is very much appreciated.

I can take a look, but the misfire you're describing sounds like an electrical or mechanical fault rather than something we'll sort out via tuning. Did you figure out why a single cylinder was running differently?