LeeM
New Member
The short story is, our 2004 Honda Civic with 250,000 freeway miles and all synthetic oil and timely maintenance must have the EGR valve removed and cleaned every 9,000 miles.
I have tried many "fixes" and I conclude I am getting light soot buildup that makes even the best quality EGR valve leak fumes and cause rough idle. I am going to focus on cleaning the valve as soon as my wife notices a problem. That will be about 9000 miles I estimate.
If you have not done it already, I suggest that this vintage Honda should have the intake manifold removed and the EGR valve gas distritution passageways should be completely cleaned. The passages must be cleaned manually. A new EGR valve and long squirt of carb cleaner only lasts a few weeks.
From reading the 7th generation Honda forums it looks to me like the unit-coil ignition system and platinum tipped spark plugs are not the usual cause of engine misfire and rough idle. Here is what I think is going on: the 2004 vintage Honda is set up to idle with a very lean fuel mixture. The slightest leak of exhaust gas or air into the intake manifold upsets the fuel mixture and causes rough idle.
Our car dies or idles rough after climbing a mountain and going downhill with throttle closed. The climbing event causes the EGR valve to stay open and pick up soot. When going downhill with throttle closed the EGR valve is supposed to be closed. What happens to my wife is rolling downhill the engine dies due to EGR valve leakage upsetting the idle mixture. I can start the engine by jabbing the gas pedal and extended cranking, like from the days of the accelerator pump on carburetor engines. The car will not idle, so I pop it into Drive and take off. The EGR valve was really leaking a lot. After 5 or 6 miles of jabbing the gas pedal, some of the crud got cleared away and the engine would idle on 3 cylinders, sort of.
If you are fighting rough idle, here are two things to try: With engine off, unplug the EGR valve and see if idle improves. Another way to test if the EGR valve is leaking exhaust gas when it is supposed to be closed is make an aluminium blocker plate out of a soda can and put it between the EGR valve and the gasket. If your rough idle problem improves then your EGR valve is leaking.
The intake manifold is made out of plastic, If you still have rough idle after eleminating the EGR valve then do the classic tests for an air leak: Check bolts for even tightness. I sprayed WD-40 on the intake manifold flanges of a cool idling engine looking for air leaks. No leaks.
Over the last 20,000 miles, the biggest engine problem has been the EGR valve being replaced, then cleaning the EGR valve gas passageways. About 10,000 miles ago the engine began running rough yet again and the clear culprit was EGR valve gas leakage at idle. So I bought a Honda Dealer EGR valve to ensure I had a quality part with a guarantee.
For the last 6,000 miles the engine has been progressively getting worse with rough idle and a really scary tendency to die and refuse to restart in heavy downhill mountain commuter traffic.
Following an earlier clue in the Civic Seventh Generation forums, I adjusted the engine valves 4,000 miles ago. I paid particular attention that none of the valves were tight. The plugs showed even combustion and temperatures all around and the cooling system passed a pressure test.
I have tried many "fixes" and I conclude I am getting light soot buildup that makes even the best quality EGR valve leak fumes and cause rough idle. I am going to focus on cleaning the valve as soon as my wife notices a problem. That will be about 9000 miles I estimate.
If you have not done it already, I suggest that this vintage Honda should have the intake manifold removed and the EGR valve gas distritution passageways should be completely cleaned. The passages must be cleaned manually. A new EGR valve and long squirt of carb cleaner only lasts a few weeks.
From reading the 7th generation Honda forums it looks to me like the unit-coil ignition system and platinum tipped spark plugs are not the usual cause of engine misfire and rough idle. Here is what I think is going on: the 2004 vintage Honda is set up to idle with a very lean fuel mixture. The slightest leak of exhaust gas or air into the intake manifold upsets the fuel mixture and causes rough idle.
Our car dies or idles rough after climbing a mountain and going downhill with throttle closed. The climbing event causes the EGR valve to stay open and pick up soot. When going downhill with throttle closed the EGR valve is supposed to be closed. What happens to my wife is rolling downhill the engine dies due to EGR valve leakage upsetting the idle mixture. I can start the engine by jabbing the gas pedal and extended cranking, like from the days of the accelerator pump on carburetor engines. The car will not idle, so I pop it into Drive and take off. The EGR valve was really leaking a lot. After 5 or 6 miles of jabbing the gas pedal, some of the crud got cleared away and the engine would idle on 3 cylinders, sort of.
If you are fighting rough idle, here are two things to try: With engine off, unplug the EGR valve and see if idle improves. Another way to test if the EGR valve is leaking exhaust gas when it is supposed to be closed is make an aluminium blocker plate out of a soda can and put it between the EGR valve and the gasket. If your rough idle problem improves then your EGR valve is leaking.
The intake manifold is made out of plastic, If you still have rough idle after eleminating the EGR valve then do the classic tests for an air leak: Check bolts for even tightness. I sprayed WD-40 on the intake manifold flanges of a cool idling engine looking for air leaks. No leaks.
Over the last 20,000 miles, the biggest engine problem has been the EGR valve being replaced, then cleaning the EGR valve gas passageways. About 10,000 miles ago the engine began running rough yet again and the clear culprit was EGR valve gas leakage at idle. So I bought a Honda Dealer EGR valve to ensure I had a quality part with a guarantee.
For the last 6,000 miles the engine has been progressively getting worse with rough idle and a really scary tendency to die and refuse to restart in heavy downhill mountain commuter traffic.
Following an earlier clue in the Civic Seventh Generation forums, I adjusted the engine valves 4,000 miles ago. I paid particular attention that none of the valves were tight. The plugs showed even combustion and temperatures all around and the cooling system passed a pressure test.