hello there
 

Hi I just bought a 93 civic vx with the d15z1 engine and i love it. There is one problem though it misses and bucks when trying to hold a constant speed which is killing my mileage. I was wondering if anyone here would have any suggestions. Anything would be greatly appreciated.

Maybe an intake air leak somewhere? If your engine speed fluctuates at idle, that might be a cause. What other symptoms do you have? Is your Civic a manual or automatic? If it bucks under load, I'd look into spark (coil packs, plugs, wires). The other thing to investigate is clogged fuel injectors or fuel filter.

its a manual trans and it idles fine, accelerates fine, does great on hills, just bucks on flat ground trying to hold constant speed. i also sprayed starting fluid around the intake and vaccum lines to check for leaks and the idle held constant. it was a little high though but all the time at around 850-900 rpms.

I think I'd get a shop to put a scope on it. It has to be air, fuel, or spark. If it acts up under light load like that, I'd suspect ignition.

It doesn't cost you anything to check the air filter, and maybe $5 for a can of fuel injector cleaner, so do those first. Pull your plugs and check their gap and condition. Lastly, disconnect your battery for 5 minutes to reset the ECM. Those are the cheap checks. You might find your problem there. If not, then it gets more expensive.

Next would be the coil packs and spark plug wires. Maybe you can find someone else with a similar Civic who'll let you swap those parts to identify your problem. Otherwise, price those parts v. the scope check, and make your choice.

Two VXs in our family. When you say constant speed, if you add a little more gas pedal or slow down a little it smoothes out? If so, after all the regular tune-up items, I'd be checking the throttle position sensor. Make sure you have the proper plugs, wires, new cap, all that stuff.

Scott

Yeah, what he said. I was going to say throttle position sensor myself, but he got there before me! Check the computer codes and see what you get.

ok, so this morning i replaced the plugs, dist cap, rotor button, fuel filter, and inspected the plug wires and air filter. Still has the miss so i guess im gonna try the tps. also i was thinking the O2 sensor since the old plugs had pretty decent carbon buildup. i was wondering if anyone knows a good way to clean the sensor since it is the 200 dollar one. another thing the engine light is not on would it still read any codes?