Ok...heres the story: 98 civic with a D16Y7. For about 6 months, had a progressive problem. Seemed like it was misfiring, or skipping, and the idle would wander from 500 rpms to about 1200. Wasnt real bad for awhile, has gotten worse in the last month. It doesnt throw any codes (no CEL light), and my scanner says 0 codes.

Here's what I have done: When the problem first started, I changed the plugs and fuel filter. Didnt fix it. Also replaced the timing belt (for mileage sake, no issues) and water pump. Also replaced valve cover gasket just ffs.

Had a thermostat go bad on me last week, so changed the thermostat, and replaced the radiator. Took the IACV off, and cleaned it with brake cleaner. Filled and burped the cooling system (parked on incline, and kept filling radiator with the heat on until no more air bubbles). Had hoped the IACV being dirty or clogged would be my idling issue. It wasnt. Possibly the IACV has gone bad and needs replaced?

Checked the plug wires, and dist cap, all good, and get a nice spark. So idling problem still occurring, and it gets worse after I drive it 10 to 15 miles. It starts stalling out when I release the throttle (such as going around a corner, or coming to a stop) after I have been driving a bit. Doesnt do that until I drive for 10 to 15 miles tho.

I havent hooked a fuel pressure guage to it (have to create a port, ugh) but I replaced the fuel pressure regulator today. Still having same issues...seems like it misfires or misses a cylinder when warm, then after driving for a 10 mile plus, it idles hard, and tries to stall when I take foot off accelerator. While accelerating, is fine.

Fuel pump works fine upon start up. But this seems to be a fuel issue to me. I poured some sea foam in the tank today, in hopes it is a dirty injector. if I see some improvement, might indicate the fuel system is dirty or clogged somewhere. Well, truth be told, I have had some ideas, but not found the problem yet. Anyone have some ideas on what could be causing it to run so rough it stalls, and why the idle goes up and down while sitting? All happens after it warms up, and gets worse the more I drive it. Oh, and I have seen the mpg go down over the last three months to where it gets about 30-35 on the hwy, and used to be closer to 40 mpg.

Any thoughts would be greatly appreciated. Thx!

 

have you tried to adjust the distributor some times if it is off it will cause it to misfire and i dont know if that can lead to the idling of the car.

 

As it drives and accelerates OK, fuel and spark seem to be OK. Quit wasting money there. Valve clearance too tight will cause misfiring at idle, so check and adjust the valves. The valves get tighter as the metal expands when the engine warms up, consistent with what you are experiencing. See if the misfiring is related to one cylinder by disconnecting the fuel injectors one at a time.

The IACV could be just plain bad. Throttle body cleaner should be used, not brake cleaner, there is a difference. Clean the passages that the IACV attaches to as well. You can try adjusting the idle air screw on the throttle body, if that keeps it running but you still have inconsistent idle speed / stalling (but not due to misfiring) IACF may need replacing.

 

i had an issue where the idle would drop while warmed up. idle stayed at 1200 and would drop to 500 and go back up.
so i loosened the throttle cable while running, and it went to 750 and stayed there.

 

OK, cleaned the passages of the IACV where its connected, they were pretty dirty. Didnt change anything. Tried to start it last night after test driving it for 30 minutes (it has sat after driving for about 2 hours) and it wouldnt start. Got it to start a few times with lots of throttle, but then it died out, in spite of me pressing the gas.

Makes me wonder about the valves being off, the way it wouldnt start and kept dieing from a cold state. Is it possible the timing belt is off? what would being off 1 gear/tooth either forward or back do/look like?

Gonna isolate each cylinder by fuel injector to see if I can find out which one is misfiring. Should I be surprised that no codes or CEL i on during all this?

 

Make sure CEL works for the bulb test (turn key on and don't start), someone may have taken the bulb out. Timing belt off by a tooth will do this kind of stuff, you should check it.

 

Turned out to be the ignition coil...ten minutes, and a new coil, and its driving like a new car. Anyone else having an issue like this, there u go.

 

I am having very similar problems with my 2002 civic. I have tried all the things you have tried even changed main relays and all that but my car still stalls/ stops after driving for 30min Please any body who knows how to fix this problem please help us out, I have my post updated frequently with everything I have done so far.
Please if you find the solution please post it here and pm me so I can also try to use that to resolve mine

thank you....

 

I am having the same problem but theidle sometimes gets low like 500 rpm I have a hx 1.6

 

do you have a hx thanks atlanta