96 Civic - Car loses acceleration, doesn't start, shuts off

That era civic had problems with the relay board that powers the fuel pump. Often worse in hot weather, it can intermittently lose power to fuel.

Lots of sites have tips to diagnose and/or replace. Good place to start because it's pretty easy to test and a fairly inexpensive part.

I'm taking a different approach to this. First, there may be multiple problems here.

First, if replacing the spark plugs temporarily solves the problem, and the car was randomly misfiring on all cylinders, then I can think of only two possible scenarios that fit that description.

1. Either the tips of the plugs are getting fouled
2. Or there is high resistance in the secondary circuit causing the spark to look for another path to ground causing carbon trails to form inside the spark plug boot, along the porcelain to the block.

There are a number of possible reasons for #1.

1. Engine running too rich: This could be due to a stuck open thermostat, a defective ECT ( Engine Coolant Temp ) Sensor, a defective oxygen sensor stuck lean, the engine burning allot of oil, and less likely a defective fuel pressure regulator or fuel pump.
2. Burning excess oil could itself foul the plugs and cause misfires, even without causing the the engine to run rich

The primary reason for #2 would be the engine running extremely lean. This could be due to either a vacuum leak, insufficient fuel pressure, or a dirty MAF sensor.

On the other hand, I can't think of any reason why fouled plugs or plugs with carbon trails would cause that crazy revving behavior and intermittent loss of power, or how that behavior could be solved by replacing said plugs. In fact, that behavior sounds allot like a defective camshaft position sensor. A defective CPS could also causing misfiring.

However, the bigger point is that it's unlikely you'll be able to properly diagnose this yourself, without a scan tool, potentially an oscilloscope and allot more knowledge than you have. My recommendation would be to take this to a competent mechanic, and in general that means one who has an oscilloscope and knows how to use it.

There's two possible things that come to mind about that Idle Bobble you're experienced, that I didn't see mentioned...

Idle Air Control (IAC)

Here's a Replacement Video from YouTube Here's a Cleaning Video from YouTube

The other thing is seemingly Honda-Specific. It's called a Fast Idle Thermo Valve.

Here's a Honda-Tech Forum Post about cleaning the FITV

The FITV can cause hunting/surging Idle, aka Idle Bobble. As far as I know it's specific to Honda. The IAC can also cause this issue.

Here is a link to a Forum post with some basic diag to determine between the IAC vs FITV

This is also one of those times where I would recommend a Motor Treatment/Detergent be introduced into the Intake/Top-End. Something like SeaFoam Motor Treatment. I URGE you to read the instructions carefully, as inducing fluid through vacuum can cause harm if you put in too much. Just given the age of the engine, I feel that it could benefit from this treatment.

I am not sure if this is the answer, but the IAC nor the FITV was mentioned, so I figured I'd throw it out there.

Obligatory clean and tighten your battery terminals, grounds, and check all fluids etc.

I hope this helps.

It could also be a vacuum leak. If you get unmetered air into the engine, it can be detected by a lean air-fuel ratio at the lambda sensor, which means the closed loop control will respond by injecting more fuel, hence the revving.

Also, a vacuum leak can definitely cause the condition of being hard to start. Too much air for the amount of fuel that is usual when starting the engine can mean there is no combustion (gasoline being combustible only at certain air-fuel ratios). No combustion, thus no start.

Because the vacuum lines are rubber, they can very well be failing on a car that is as old as 20 years old.

Maybe it could be the fuel injectors or the fuel pump that has gone bad or is clogged, are all 4 cylinders getting good compression? It could be a valvetrain problem but with the spark plug situation I highly believe it to be the fuel system if it's getting spark.

Edit: did you check out your fuel filter? Not enough fuel means not enough power!!!!