I have a 98 honda civic ex that only misfires in the morning what could it be?

It turns on fine at any other time of the day and once it gets warmed up the misfire also goes away and drives fine. I have.replaced the fuel pump, fuel filter, spark plugs, distributor cap. Could some one please help narrow it down to avoid me spending alot of money trying to fix it?

Have the car check out at your local Auto Zone or Advance auto part stores for free. They'll read out the code and give you a print out with the recommendations of repair. You'll need the code(s) to guide you to the right path of diagnose the misfire problem. Was it misfire or running rough or irregular idling when cold? Any smoke upon cold starting? Did you replace the spark plug cables? Or have you checked out the ICM (Ignition Control Module). Fuel pressure reading?

Anyway, the sensor(s) responsible and control upon cold start will be the IACV (Idle Air Control Valve), the ECT (Engine Coolant Temperature ) and the IAT (Intake Air Temperature) sensors. I would check into these three sensors first.

I know that it is only happening cold and most likely with fast idle, once the car warms up, and steady idle with no misfire, what is the MAP voltage, should be just a hair under 1V DC, can be just a hair over but anything other than this tight range will require engine valves adjustment.

Simply running rich as cold start will be a clogged induction system and IACV bypass airway and dirty throttle body as a whole and / or an out of range, severely cold, ECT sensor, its in its operating range even it it says minus 40 degrees so it will not set a code, monitor the voltage from start to about 1 minute (or more) and look for a major change in voltage at about the 30 second mark. Old school as I don't know what test equipment you have, see which cylinder is misfiring, change that plug to different cylinder the next AM prior to starting, does misfire follow plug, if not, injector swap is in order, if did not follow injector again, then low compression looks like your culprit on cold start. Is only one cylinder or multiple misfiring, random? Start checking the condition of the new spark plugs in AM and see if it has oil. Oil in the cylinder will smoke but fresh plugs should not misfire without over rich mixture from ECT sensor too cold initially.

Also focus on the fuel system. What is coolant temp readings before start up & also check you static fuel pressure by priming the injectors(cycle the key for 3 seconds) & pinch off BOTH the return & feed lines. Watch for fuel pressure drop. 10psi in 10 min is too much. I have solved many misfired codes and related issues by cleaning injectors on the inside clean the carbon off the injector or do an injector balance test.

Another thing is the O2 sensor (Before CAT) It should read ranges from 0.18 to 0.92 vlts when engine speed are held at 2500 Rpms. Snap throttle and it will range from 0.0 to 0.99 vlts. Have a scope will help, scoped the sensor and it matched the scan tool. In the morning, test drive while monitoring the O2 with the scan tool. While driving at a steady speed of about 50 mph the O2 should go from ranging between 0.20 v and 0.85 v, to between 0.4v and 0.85v. Push on the throttle and the O2 will climb to over 0.98v. Let off the throttle and it will drop to 0.0v. If not, replace the O2.

Have a compression test or leak down on engine as sounds like hair line crack in head gasket between cylinders causing misfire or intake gasket leaking and sealed off when the engine warm up.

There are more, but update the needed to know information and E mail me so I can be more helpful as I'm guessing right now. At least get the code(s) read out. HTH

Edit: Just in case you need for testing, this link contains all wiring diagrams for your Civic Ex. The figure #3 is for the sensors that I have mentioned above:
http://www.autozone.com/...528018f8b2

It's a problem in the start plug. You should take it to a Honda mechanic and have it fixed.

Go out at night with a bottle of windex. With the vehicle running, saturate the ignition system on the car, you know, plugs wires distributor cap. Do you see fireworks? I'm betting dew is causing your ignition to go to ground causing a miss, and when it dries, its fine.

Hi, I've heard the oxygen sensor on you manifold does not allow the car rev to it's minimal revs from a cold start to let the computer adjust the fuel/air mixture… Build up from the sulphur from the fuel… Do not clean, better of replacing the sensor… Hope this helps.

Its the problem of start plug…