Misfire and Rough Idle
 

I am having a problem with misfire at idle and a rough idle on my 2000 Civic LX Manual Transmission (D16Y7 engine). I have replaced the spark plugs, wireset, distributor cap, rotor, to no avail. The car was misfiring in cylinder 1 (ECU code P0301). I then replaced the distributor and adjusted the ignition timing, and this stopped the misfire for about a week. When it returned, I was receiving misfire codes on all of the cylinders, but primarily on cylinders 2 and 4 (P0302 and P0304). I have checked the resistance across the fuel injectors, and all were to the specification shown in the Hayne's manual. I have checked the vacuum lines for leaks, to the best of my ability, and none were found. The misfiring only happens at relatively low RPMs (600-1200), and then the car smooths out. The short term fuel trim when first started hovers around 10%, but after holding the car at 1500RPM, it drops to about 3% when returning to idle. When accelerating, the short term fuel trim hovers around -20%, increasing to -5% or so when being held at a constant speed, and higher RPMs (about 1500+). The fuel economy has dropped from 38mpg on average to 32mpg on average. Any help determining the problem would be appreciated.

Re: Misfire and Rough Idle
 

Hmmm this could be a couple of things. Do you have the spark plug wires in the right firing order. It could possibly be the fuel pump or filter.

Re: Misfire and Rough Idle
 

I'm not going to say that I know what the problem is, because I don't, but I have some suggestions about what to look at anyhow. I would double check the spark plugs. Look at them to see the condition and gap and if they are the correct plugs. Just because you took out plugs with the same model doesn't mean the correct plugs(and gap) was in there before. Another thing to check is your distributor rotor and cap. I have heard a lot of people say that some of the aftermarket ones are not very good, and to go with Honda OEM parts there. I personally can say that my aftermarket ones worked fine in my case. Good luck with your troubleshooting!

Re: Misfire and Rough Idle
 

Sounds like a clogged injector. "I have checked the resistance across the fuel injectors, and all were to the specification shown in the Hayne's manual." Doesnt mean the injector is not clogged up. Just shows you its working . A small percentage of block can make a huge difference. Do a compression test too.

Re: Misfire and Rough Idle
 

I had put Seafoam into the fuel to try to clean the injectors, but the misfire is still happening. I do realize that I should take them off of the car and get them professionally cleaned. I replaced the fuel filter with no luck. I will check the compression as soon as I can get hold of a gauge. Thanks for the help.

Re: Misfire and Rough Idle
 

Try using real injector cleaner, not that sea foam crap. Chevron makes a good one.

Check your coil, and see of it has a weak spark.

Could be a clogged fuel filter. These are often overlooked and can make a huge difference.

Your injector could be damaged/cracked take em all off and inspect them. If you are going to look into getting them professionally cleaned, sometimes it is cheaper to just buy new ones.

If none of that stuff helps, then you might want to look at the fuel pressure regulator.