2000 Civic LX. My engine will catch when loaded at low RPM. Gas mileage is 5 mpg less than it once was. This catch happens only when the engine is warm, only when RPMs less than 2000, and especially when attempting to accelerate in these conditions. A good example is on the highway when traffic has slowed to 55 and I try to get back up to 65 in 5th gear.The car will buck and protest. Here's what has been done recently.
-New plugs and wires, good gap, checked for arcing in the dark.
-New distributor cap and rotor (the old one looked perfect though)
-New fuel filter
-New PCV valve
-New air filter
-Oil/filter change
-Fuel injector cleaner through gas tank
-New primary O2 sensor (it threw a code after doing the above, so my fault)

My radiator fluid is original (95,000 miles). I've neglected doing this because the fluid appears fairly clean and free of any particulatematter. I've never lubricated the throttle body or cables, I guess I should. The transmission fluid is likely due as well as the clutch fluid, but this thing does not seem to be related to the drivetrain (or is it?). I'm just trying to think of outstanding maintenance to ring some bells out there.

Where do I go from here? Could this be computer related? Could itbe fuel pump/supply line problem? How do I check these things? What about the exhaust system? I replaced a section of exhause from the resonator back, but the portion from there to the catalytic convertor is original. Please don't suggest this has anything to do with the kitty unless you've got some good backup. $600 I haven't got! Any other ideas?

 

you let it drop below 2k in 5th on the highway?! why?? just downshift into 4th or 3rd.

 

I'm not sure how this answers my questions, but I'll answer yours. Spending a lot of time in fifth gear got me 40 mpg regularly and upwards of 45 on a long trip. I'm not a sporty driver. A gently transistion from 55 to 65 is nice and easy on the car.

 

I'm just saying that letting the RPM drop that low is surely going to cause the engine to bog down.

 

Can't help but wonder if there's an intake leak somewhere. Low RPM, high load will cause those conditions with an intake leak. Certainly not THE only thing, but worth a look see. If it did it under conditions recreatable in the driveway, you could use starting fluid around the intake to see if the rpms changed. Other than a leakdown test, I'm not sure how you would check for this condition.

 

OK, could you be more specific for a novice mechanic. The codition is repeatable, because if I idle the car in the driveway after the engine is hot, I usually will get the occasional engine catch. However, they will be spaced out at random intervals, say 5 to 30 seconds apart. What exactly am I doing with the starting fluid and when? Is the intake the black box to the left of the air filter assembly? I don't fully grasp whata leak there would mean since air goes in there anyway. Thanks.

 

Damn, easier to just do than to try and explain.
Air comes in through the inlet INTO the intake. The intake is where the atomization of the gas takes place, before it is sucked into the combustion chamber for firing. If the seal between the intake and the engine head is compromised, this can create improper atomization of the gasses and throw off the air/fuel mixture. I used this technique back when, *GASP*, cars had carburetors. Problem will arise when you try to spray the "bottom" of the intake on the back of the engine. Hella-hard to get to. Being so new to this whole, transverse mounted I-4 thing, I'm not sure if codes would be thrown during this "catch" if the air/fuel mixture was that off. Honestly I dunno. Your best avenue might be to just visit your local mechanic, and let him/her hear it.

 

Here's what an intake manifuld looks like.

 

Cost dictates that I am my own local mechanic (and I like to learn). So you're saying that if there's a leak there, it will suck in the starter fluid and cause a brief RPM increase. Regarding the codes, none have been thrown except for that O2 sensor thing which I believe I fouled with the FI cleaner. Based on your picture of the manifold, are you saying a problematic leak could occur at those four exit ports after atomization?

 

yes. Though your intake probably won't look like the one pictured, it's just an example. The four ports are the intake ports to your engine's head. Here there is a gasket that seals the intake to the head.

One question though, that just struck me. Did you have this problem prior to all of the aforementioned work? Or did the problem come up after the work was done?