Engine Noise Combined With Acceleration Vibration

[Tydirium]

Good day. May I please have some guidance and thoughts regarding an issue with my 1991 300ZX Z32, twin turbo, automatic:

-After sitting for a few days, last weekend the car started up fine, drove on back roads, maybe five minute drive going 45mph. When I got to a stop light, the engine was making a "dub dub dub dub" sound almost like a cylinder was misfiring. When I let my foot off of the brake to creep into the intersection the car was lightly jerking in time with the "dubs", not a smooth coast.

-When I accelerated the car vibrates; higher the speed / RPM the worse the vibrations. When I let my foot off of the gas at speed and let it coast, the vibrations cease. So the vibrations are being caused when the engine is being asked to work.

Today I spent a few hours changing the spark plugs, checking all coil packs and coil harnesses (harnesses are a couple years old, look fine), changed the vacuum tube o-rings. Started it up and the same thing: it ran great then within 5 minutes of driving / warming up going 45mph the "dub dub" was back as well as the vibrations.

No warning lights on the dash, not overheating, fuel & air filters changed in March, oil level fine, antifreeze level fine, no weird smells. The only other thing I have seen over the past couple months is slow drip liquid near the driver rear area; the window washer fluid tank is back there and as the liquid does not feel slippery nor have a distinct odor I assume (maybe falsely?) it is washer fluid. Thanks very much for the help.

[Daspyda]

Did you check the injectors? It seems you have one cylinder bad.

[Tydirium]

Injectors, not yet. I started with the spark plugs / check coil packs etc. This week I changed out the fuel damper and fuel regulator as both were quite old, fuel temp sensor is arriving this week & will also be changed out for the existing old one.

Any advice please on how to check the injectors? Thanks for the help.

[Daspyda]

With age comes degradation.

https://conceptzperformance.com/wiki/in ... or_Testing

[Daspyda]

Your washer fluid drips from the front, and you can add colored liquid to test. Your A/C condenser/system always drips after a drive, and I think it drips about where the wheel distance from the front bumper is, on the right passenger side of the engine.

[Tydirium]

Thanks Daspyda. My last two steps in trouble shooting the fuel system is the replace the fuel temp sensor and add some Chevron Techron fuel injection cleaner with fresh 93 octane gas to see if that helps.

I just pulled a couple of the more easily accessible injector cable connectors off and they looked pretty clean and the "new" style i.e. they have been replaced within the past few years. Will check the others & ohm check all of the injectors this week.

You brought up a very interesting point. The AC has been long dead, depleted & no longer used. However I have noticed what appears to be a slow windshield fluid leak somewhere on the driver side of the vehicle. I have not recently washed the windshield however are there any specific points near the tubing routing that could directly affect the injection system, or more of a general comments towards potential for added humidity / liquid under the hood? Thanks again for the help.