What causes the start to feel rough?
 

The 1993 Accord starts up fine, this isn't a no-start or intermittent no-start problem.

The problem is after the car has been left unused overnight, when the car is started up it shakes/vibrates hard and then immediately afterwards it's nice and smooth.

I don't know if this makes sense but it also feels like the engine is going too fast when it starts up. I know for a fact that as soon as the engine catches the idle shoots up to past 1000, maybe even 2000. But after waiting a while it decreases gradually over a span of about ten minutes until it hits 750.

If the car has been used however and then you attempt to start it up after the engine has been off only for about three hours then the car starts up smoothly, not rough at all and as soon as it starts up the idle shoots to about 850 and then quickly goes down to 750 where it should be.

Does this have anything to do with the drainback of oil? I just changed the oil and replaced the filter with a Denso that's supposed to have a silicone drainback valve but this problem has been around for a while.

I don't know what would specifically cause this.

Before you go start your car after it sits all night, turn the key to the II position, but do not try to start the car. Turn off the key and turn to II. Repeat for a total of three times. Then try starting the car. Did this stop the initial vibration?

Initial rough start w/ immediate smoothing is a symptom of leaking head gasket, but could be other things.

If you allow car to sit overnight, remove spark plugs and turn engine over. If you see water spraying from spark plug holes, you have a leaking head gasket.

Other things are weak spark plugs, wires, cracked rotor, or distributor cap.

good luck

I thought if it was a leaking head gasket I would see bubbles in the radiator? I took off the radiator cap while the engine was running (before it got hot) and watched it for about two minutes and saw no bubbles. In addition the exhaust isn't giving off a colored smoke either which I heard was indicative of burning coolant.

I'm going to try both of your suggestions. Is it safe to crank with the spark plugs removed though?

As for the cap, the cap terminals inside the cap are worn somewhat badly, almost as if they've been rubbed by the rotor. The rotor is also corroded and worn, it's missing a bit of the contact surface.

I already have a replacement cap and rotor from Honda but I haven't gotten around to changing it because I wanted to do it when I remove the entire distributor and change the O-Ring also. I think the oil leak I've also been having is coming from there because I thought it was leaking inside the distributor but I cleaned it out and drove it around for a good two weeks, pulled the cap off and there was no oil in there. However, there was oil on the underside of the distributor which I had cleaned up before. This leads me to believe the O-Ring is leaking oil that is pooling on the underside of the distributor.

I'll do all of the testing and replacing the O-Ring, cap and rotor tomorrow. Thanks!

If you are going to try to start the car without the spark plugs connected, unplug the distributor connectors. You don't want the spark you generate grounding through the coil and damaging it.

Head gasket leaks can take many paths and may be intermittent. Exhaust into the coolant system is not always the case. I had a bad HG on 94EX that only showed when car was warmed, driven, and shut-off for 1/2 hr. On restart it would run rough for a few seconds and smooth out. I could not detect exhaust bubbles or white smoke.

You only need to turn engine over 1-2 revs to see water spray, if it's there.

good luck

this also could be a fuel problem . If the car leaks it fuel back into the tank you will get them symptoms. if it was anything else most likely it would happen on every start . two possibilities ,either your fuel press regulator has a small leak or the check vlv in your fuel pump is leaking by.

X2. The bad head gasket caused my 96LX to run rough for three or four seconds after an overnight cold start. The only other symptom was a loss of a quart of coolant every ~200 miles.