97 EGR issue

[Goof]

Hi Everyone,

 

Having a small problem and hope someone has some insight. Sorry for the wordy post but I tend to work like that, as details tend to help on any forum.

 

A few weeks ago out of nowhere, my 97 Prelude base, stock (125K miles) logged the legendary DTC 80 / P0401 EGR code. The engine has been flawless ever since I bought it 7 years ago or so. The idle has always been 1000 to 1200 cold and 700 to 800 warm and never deviated, so the DTC was kind of a surprise. I meticulously maintain it myself, change the oil every 2500 to 3K miles, all fluids every year and, meh.. You get the idea..

 

After some online research and a couple of hours with the service manual, I ordered a new EGR gasket and 10 of the EGR plugs as the process seemed pretty straightforward. Last weekend was the target date for the cleaning job as it was the first time the outside temps have been above the low 20's in a few weeks.

 

The removal of the EGR valve is straightforward and took about 20 minutes. Penetrating lubricant is your friend here as I broke a ¼” drive ratchet extension in the process. The surprise was that it was fairly clean. There was a little buildup on the pin but the valve operated smoothly. After a thorough douching in carb cleaner it looked and appeared to operate like new. The item of note here is that the only vacuum line that was disturbed in the whole process was the line to the EGR valve.

 

Then I started in on the plugs. Not quite as easy as it was cold as hell. I pulled the first plug on the passenger side and it was quite clean. There was a touch of discoloration that I cleaned up with some carb cleaner, swabs and an air gun. Being glad I bought extra plugs as I disfigured the first one I tried to install.

 

After a warm up inside, I removed the opposite plug closest to the driver side as I thought this would give me a good idea of the rest of them. That in mind, this plug was a total bitch to get out. Broke two screws and had to drill it three times before it came out. The result also stunned me. That port was only discolored with no serious buildup. After cleaning that one the same as the first one, I installed a new plug and decided to call it a freezing afternoon. I installed the newly cleaned EGR valve with the new gasket and replaced the ignition coil.

 

Here’s the rub.. After clearing the DTC and starting the engine, it ran slightly rough for a few minutes (which I expected with all the carb cleaner I shot into there) and then settled in on it’s normal 1000 to 1200 cold idle cycle. Everything looked good. After a few minutes, it dropped to it’s normal 800 rpm idle, so I took it for a drive. Everything seemed ok and after a while I ran it hard at times to clear things out and it was working great. That was until I came to a stop. The engine slowed to 800 and then down to 500 then to 200, rattled a bit and then searched for an idle again.

 

It now does this predictably and I have to feather the throttle coming off any deceleration or the engine will settle at around 200 rpm and shudder before the ECM tries to find an idle. It has not stalled as of yet but comes damn close. Otherwise, throttle response is typical of previous performance.

 

With the relative cleanliness of the EGR and the two fairly clean EGR plugs, I have not pulled the IACV nor messed with the EICV as a couple of days ago the entire system worked within perfectly within tolerance. The system has not thrown any DTC since the cleaning of the EGR valve..

 

What puzzles me is that I understand that 90%+ of all idle problems are caused by a vacuum leak somewhere. As noted earlier, the only vacuum line that was disturbed was the line to the newly cleaned EGR valve.

 

While I understand that the systems are interconnected, what in the hell would cause this idle problem? My only guess at this point is air in the coolant lines which I checked this afternoon. Got home after a good run on the freeway and then parked it while leaving it running. Then popped the radiator cap and left it to run for about 20 minutes. It was bubble free so I don’t account a air gap on the IACV.. I would also assume that the primary O2 sensor is ok as no DTC’s have been logged..

 

To date, still no DTC, no answer and a Prelude that wants to stall only after it warms up.

 

Again, sorry for the lengthy post but a mere three days ago the engine was operating perfectly. Carb cleaner, a new gasket, a couple of EGR plugs and things go South..

 

I’m confused.. Does anyone have any sage advice?

 

Thanks in advance for any shared wisdom.

[Turtlehead]

Could be a vaccum leak on the intake, either a gasket (possibly the EGR gasket) or possibly one of the plugs you replaced. The EGR should be "closed" while at idle speed so there should be no vacuum to the EGR valve. Next time it does it take a pair of pliers and pinch the vacuum line at the EGR valve and post back with how the engine responds. If you disconnect the vacuum line to the EGR with the engine warm and at idle speed put your finger over the hose end and feel for vacuum, if there is vacuum then with the vac line disconnected, disconnect the 2-pin electrical connector that goes to the EGR valve and post back with how the engine responds and check that there is no longer vacuum to the vac line. I will not get to much more into the EGR diagnosis because it sounds more like a leak on the intake, but it could be that the EGR valve is lifted (open) at idle speed and that can cause your idle drop. This is all assuming this was not happening prior to your repair work.

[Goof]

Could be a vaccum leak on the intake, either a gasket (possibly the EGR gasket) or possibly one of the plugs you replaced. The EGR should be "closed" while at idle speed so there should be no vacuum to the EGR valve. Next time it does it take a pair of pliers and pinch the vacuum line at the EGR valve and post back with how the engine responds. If you disconnect the vacuum line to the EGR with the engine warm and at idle speed put your finger over the hose end and feel for vacuum, if there is vacuum then with the vac line disconnected, disconnect the 2-pin electrical connector that goes to the EGR valve and post back with how the engine responds and check that there is no longer vacuum to the vac line. I will not get to much more into the EGR diagnosis because it sounds more like a leak on the intake, but it could be that the EGR valve is lifted (open) at idle speed and that can cause your idle drop. This is all assuming this was not happening prior to your repair work.

 

Thank you very much for the advice. I apologize for not getting back to you earlier.

 

I can confirm that the EGR valve is indeed closed at warm idle. Both block of the vacuum line and disconnect of the solenoid leads don't have any real effect. Idle still 500+-, usually -. With the engine off and warm, I can hear and physically "feel" the valve open and close completely. I can hear the "tick" when I retract it and let it go, so having cleaned it recently myself, I assume that it's seating properly metal to metal and not metal to carbon deposit, leaving the valve open.

 

I did some other minor cleaning around the intake and didn't see a culprit that would lead me to anything. I also visually checked all of the vacuum lines (as I don't have a vacuum pump) and everything appeared to be in order, but what do I know without the correct tool to test it. The IACV also looked clean inside. The screen had some minor discoloration but nothing that I thought would promote my current issue.

 

The only thing lurking in my head is if the carb cleaner used in the EGR plug replacement could potentially degrade the intake manifold gasket and have a hand in this. The other is the plugs. After flushing a bunch of crap through the system, is it possible that a plug is fouled and adding to the stack of symptoms?

 

Still scratching my head, but definitely appreciate the help.

 

Thanks,

 

Steve