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I have a 94 Civic EX. The engine typically runs great when it is just started or just warm, but when it gets hot (like during a lot of stop and go driving etc.) it develops a miss at idle. It is only every now and then (like every 5-20 seconds), and is much more noticeable with the AC on. It never misses immediately after I stop, but only after the car sits at idle for 30 seconds or so does it start.

When the weather is EXTREMELY hot however (line 98+), the missing is MUCH worse. The engine misses a lot at idle (like every 5 seconds or more) but it hasn't ever stalled. Twice it has bogged down horribly when accelerating from a stop. Both times it felt like the car was running on two cylinders was running on two cylinders, and the harder I pressed the accelerator the more it bogged down....then suddenly it "let go" and the car pulled like nothing was ever wrong, then it bogged down again for a moment, then it pulled again and went away. The missing at idle did not go away however after the car pulled well. Again it is worse with the AC on. The car seems to run like crap in general when it is extremely hot outside.

I do not associate the miss with the compressor turning on and off. The compressor is also only a few months old. The idle speed is fine with AC on or off, just the intermittent miss. I don't notice any missing when driving, but the car definitely looses power when it is really hot outside...seems fine in cooler weather, except still misses at idle, just not as bad. The compressor fan does turn on with the compressor. I have not checked the other fan, but again no obvious overheating based on the dash gauge.

I checked the rotor and cap, and they seem fine (distributor is about 6 years old, as is the cap an rotor). The coil resistance checks out OK, but of course that is being checked when the parts are cool. Screws on coil are a little corroded/covered with white powder, but nothing appears melted or charred in the distributor. My wires are probably 8 years old, but look good, the resistance checks out fine (when cool of course), and I don't see any arching when observed in the dark.

My intake air temperature sensor checked out fine. My injectors are only a few months old and the fuel filter was replaced with them. The Idle Air Control Valve has been cleaned. The radiator is full, and the level is not changing. My temperature gauge is a little below the center line, just like always.

The spark plugs are fairly new, and I pulled and cleaned them just to be safe. They were only slightly dirty with a little black around the rim and a white tint on the electrode. They were not blistered or anything, and looked great after a wire brushing (gap good, electrode shape sharp, no blistered metal, etc.).

I found when this all started that I had WAY too much oil in the engine (like a quart over), and attributed it to a recent oil change (had 1000 miles on change) that was done at a quick lube place. The oil was dark when I removed it, but did not appear to have water in it. It had a slight gasoline smell, but I would have expected it to smell much stronger if I had a quart of gasoline in 3.2 quarts of oil. Could be a coincidence, but could also be a symptom. I have been monitoring the oil level since I changed it about two weeks ago, but so far there is no change in the oil level or the oil color. I suspected that changing the oil and putting in the right amount would fix the problem, but it did not.

My muffler was making a rattling noise, so I decided to have it checked. It was falling apart inside, so I replaced it just in case it was plugged. That did not fix the problem either. The Cat is a Magnaflow, and was replaced only about 8 months ago.

I have a wide band O2 sensor that was installed about 8 months ago. When I feel the miss, the reading goes just a little rich, but jumps back to normal quickly. Almost hard to see because it blips so quickly. I did not notice the a/f ratio the two times the car bogged down.

The engine is supercharged, but I can't attribute any of this to the supercharger. Under load the car seems to run great, except again the couple times it bogged down in extremely hot weather. The computer has a Hondata chip, and the car was dyno tuned about 8 months ago. It ran great for 8 months, until this all started.

Any thoughts?

Thanks,

JT

 
Rep Power: 0

Check fuel pressure,, just went through the same issues with a 95 ex and come to find out it was only putting out 20-24 psi. The pump is supposed to be putting out 40-47 psi on a constant. Hope this helps

 
Rep Power: 0

Thanks, I will check. I have a permanent fuel pressure gauge under the hood, but never thought to check. I have been focusing on electrical stuff since it only happens hot, but I suppose I shouldn't focus too much and miss something obvious.

 
Rep Power: 0

I checked the fuel pressure, and that was not the problem. Based on numerous suggestions, I bit the bullet and replaced the coil despite the fact that it checked out OK when cool. While the engine seems to run smoother in general, this did not fix the hard miss when the engine is extremely hot and at idle.

 
Rep Power: 0

I had a similar issue till this last week and I went about replacing and cleaning a number of things.
Started with the dizzy coil, cleaned the rotor, replaced the cap, moved on.
Replaced the spark plugs, improved missing a little.
Adjusted timing, more miss issues resolved.
I then took apart the throttle almost entirely and cleaned the whole thing down plus all hoses in the area to get carbon crap removed, this smoothed out a cough i had at sudden acceleration.
The last thing I did was to do a coolant flush and bleed, i had air in my system. Not much but enough that I could swear when the engine warmed, the bubble in the line was bobbing around and acting as the issue. Finished the flush and have no cough or missing now. May not be your issue but worth checking since air in the coolant can cause numerous symptoms.
I also removed and replaced the o2, hopefully being yours is young this isnt a problem but may be worth looking at.
Ah before i forget, and to cap this long post. How old is your fuel filter? always a chance though seems illogical. Im banking on coolant or timing myself. The two played on eachother in my 95 and it wasnt settled till i fixed them both. I kept trying to compensate with idle, timing, etc and it never stopped till i got the air all out.