My car is a 1990 DX, but I have a single cam ZC engine in the car with DPFI. The engine was originally carbureted before it came to me.

I have been dealing with an idle issue for the last several months. When I start the car from cold, it idles fine - high idle as expected. However, after a few minutes, it will start to act like it is running on only 2 or 3 cylinders...the idle drops way down, runs extremely rough for about 5-10 seconds, but then it recovers. When it recovers, the idle will shoot up over 2,000 RPM, then try to lower back to a more normal idle speed. Sometimes it maintains a normal idle for 15 or so seconds, then the cycle repeats, with the idle dipping very low and rough like it isn't running on all 4 cylinders. There are no CELs either. Another related symptom that makes me think it is ignition related is that right before / right as it starts running rough, the tachometer needle starts flicking down to very low RPMs. I had tachometer needle issues in the past (different Civic) when my ignitor in my distributor was going bad, but I have had three different distributors present this same issue in the last year or so. I ran a Distributor King distributor from 2010 / 303K miles all the way to February 2017 / 400K miles. That was when I swapped in a World Power Systems distributor, but it only lasted 3K miles before the rotor came apart. I ran the old Distributor King until Rock Auto could replace the faulty distributor for me, and I have been running the new WPS distributor for about 4 months. All that to say all 3 distributors have given me the same idle issue.

I'm also having issues with my car eating spark plugs on the #2 cylinder. See the picture below. These plugs were brand new in August of this year, and 4 months later, it looks very pitted. Also, it was a bear to get out...I though it was going to break off in the head. This is the second set I have put on this year. I have also put in a new fuel filter 2 months ago without that solving the issue.

So...my questions:

1. Has anyone seen spark plugs get eaten like this before, especially on just one cylinder? What could cause the plug to corrode / get so beat up in such a short amount of time? Could it somehow be related to poor fuel distribution to the #2 cylinder from the DPFI system? I'm planning an MPFI swap, but still need just a few more pieces.
2. Does anyone think the spark plug issue and idle issue are related? If so, how?
3. Does anyone have any idea about the idle issue and the related tachometer needle dipping quickly? What could it be besides distributor components going bad? Grounds?

 

Well, I ended up putting in a set of new plugs and all new vacuum lines. I also took off and took apart the DPFI throttle body to see if there was anything obviously wrong there. I did notice the inside of the plenum was sparkling clean and covered in gas - is this normal for throttle body injection? I put everything back together and took it to get emissions and failed (just barely) for hydrocarbons. The car did run better with the new plugs, but the tachometer needle did flick a few times. I bit the bullet last night and went ahead and picked up a TD02U distributor, which is the last thing I need to complete my MPFI swap. I'm going to swap over this weekend and hope that corrects all of the above issues. However, I'm still curious if anyone has any input on the questions above.

 

Old car.
That spark plug is dirty! Very fouled.
Pull your new spark plugs and have a look at how they are doing. My guess is you will find that same #2 cylinder is already starting to show signs of fouling again.
Hydrocarbons are basically unburnt fuel so i'm not surprised by the fouling.

You could have a number of things going on here.
It could be something in the ignition like a bad spark plug wire or a cap/rotor issue. Best to just replace all on an old motor.
There could be damage in your #2 cylinder which you should be able to verify with a compression test.
A leaky head gasket can also be the culprit.
There may be an issue with your valves with a guide or seal being worn out.

 

Well, I completed the MPFI swap and the car idles and runs so much better. I'll be pulling plugs along the way to see if that issue improves as well.

 

Almost a year later, and the plugs look good. MPFI swap has been one of the best things I've done for how the car runs in every aspect.