Honda Civic 1.5 vtec Sport 2000 year uneven idle Help Please
 

Hello all,

I'm new to this forum hope this has not been posted anywhere else. I have a problem with my car which is hunting me for 2 months now. Basically it is like if one of the cylinders wouldn't work. When the engine is in idle the RPM fluctuates between 500 and 1000 but this is very random. Also sometimes when I press the throttle gently I get uneven acceleration the engine looses power. If I put my foot down normally the engine revs up nice and fine. Also when the throttle is fully pressed and I let it go the rev doesn't go back to idle immediately. Or when I accelerate and quickly release the throttle and press the clutch the engine revs up the quicker I press the clutch the more. It goes up about 500-1000RPM. The mechanic reckons that this is to do with the throttle body. I don't know if these two problems are related to each other.
Now I've checked the HT leads the injector leads have been replaced. Also the distributor has been replaced as well and I'm still getting the same problem. The car just had a full service with the cambelt replaced as well so spark plugs are not an issue. All the things which are related to the ignition system have been checked now. Also a diagnostic on the on board computer has been carried out shoing no problems.
I've taken the car to two different mechanics now but neither of them could fix the problem permanently. I think they couldn't find what might cause the issue.
If someone could give me some advices regarding what to do I would be really happy. Maybe a good place to take the car near Brighton area ?

The car is X reg and is the 1.5 vtec engine - D15Z6 I think.
Thanks for the help
Csaba

Try and see if it has consistently one bad cylinder by disconnecting the fuel injectors one at a time while idling. Disconnecting a good cylinder makes the engine slow down and run worse. Disconnecting a bad cylinder has no effect. This is the standard test when you think the engine is running on only 3 cylinders.

Is it a mechanical throttle cable, or "drive by wire"? Mechanical cable versions have an idle air control valve that gets dirty. Also the cable can get sticky and cause failure to slow down when the pedal is released.

@MK378
Thanks for the advices. I've tried taking of the HT lead to see which cylinder has a problem. There is one where removing the HT lead causes noticable less drop in power then the others, but there is some drop in power which lead me to think that the cylinder is running somehow.
The cable is mechanical I think however I will check this. Also good idea on the idle air control valve I'll check that.

What do you think can cause symptoms like this other than the ignition system ?

Thanks
Csaba