After spending much time trying to fathom a solution by reading and pieceing things together, I am still left with no solution, so here is my plight.

2000 Accord 3.0L(104K miles)
Started juddering or quivering under light to medium load and at around 55mph. Also seemed to be lacking somewhat in power with some unusual shifting going on.. No CEL and no codes. Installed new plugs(Bosch platinum--not NGK, I know). and after testing the EGR valve according to Haynes(tested good), I removed it and also the intake manifold and cleaned up the ports. Still juddering as before. So today, I pulled the plug off the EGR valve and drove the car about 20 miles. It operated normally--no judder and normal power. That made the auto tranny work normally as well. Of course, it threw a P1491 code indicating insufficient EGR valve lift. What are the ramifications of running with the EGR valve always closed, and what would be the effect of a faulty thermostat causing running temp to be too low?
Should I spring for a diagnostic test or can you tell me the most likely cause of the faulty signals to the EGR.

Thanks

 

Anybody???????????????

 

The Exhaust Gasses being Recirculated cools combustion chamber temp, the gasses also enrichen the burn.
A T-stat that is stuck open keeping engine temp too low will prevent the EGR from functioning.
The MAP Sensor is the 'snitch' for the EGR mal-function.
When the computer commands on the EGR valve the MAP sensor looks for a change in the Manifold Absolute Pressure.

 

Thanks Hondadude-----Those are the kind of things that I was looking for. I have not yet measured the operating temp., but I suspect that the STAT may be opened a bit. The heater is not throwing as much heat anymore, and I could feel the upper rad hose getting warm along with the engine on intial warm up--so I guess it would be a good move to simply replace the STAT and hope that it solves the EGR issue.

I will report back, but if you have any more words of wisdom, I am all ears
Thanks

 

I have more or less ruled out a faulty t-stat as the cause. I used a progressive blocking of the rads to raise the engine operating temp up to a mid level on the guage. I still get the stuttering symptom while under mid load conditions, and when I disconnect the EGR valve, the engine is smooth as silk. So is this condition caused by a faulty EGR valve unit, or is it caused by something else feeding the EGR bad input?
Is it possible that the EGR valve is fluttering at the same rate as the stuttering of the engine??

 

Update----I ordered a new EGR valve, and while I had the old one off, I bench tested it and it worked exactly like the new one--ie, when I applied 12v to terminals 4 and 6, the valve opened exactly the same on old and new. So I am thinking it is not the EGR valve. Plus, during the last 10 days while I was waiting, the car now seems to operate poorly with and without the EGR valve plugged in. It is getting progressively worse--that is, it quivers and shakes, has very little power and will now actually bog when I really step on the gas.
I took it to Honda service and they told me that if it was not throwing any codes, a diagnostic would not tell much. True or not?????

So am I faced with a process of elimination here, and if so, what is the best place to start---mass air flow sensor, TPI, fuel pressure, cat converter???????

I am stumped right now. Help please.

 

Would really appreciate some guidance here----especially about any benefits of having a diagnostics run on the car. Will it tell me anything in this case??

 

Well, since nobody has come up with any further suggestions, I started to dig a bit deeper into my car's problem. I had replaced the EGR valve with no results--now have two of those--and I replaced both O2 sensors(not a bad idea anyway, at 185,000 KMS) That changed nothing. So I just sat in the yard and reved up the engine. It would bog at 4000 and drop back to about 3800 with a lot of throttle. I undid the fron flange of the CAT and tried the RPM thing again---all the way up to the park position rev limiter of 5000 rpm with no effort at all. Bingo--blocked CAT. Below is a response I made to another post about CATS and O2 sensor

I have been dealing with a very similar problem. The only reason that the rear O2 sensor is there is so the ECU can detect the efficiency of the CAT(look for certain electric signals to compare to signals from the front O2 sensor. You may only have a bad rear O2 and the CAT may be fine. Have you had any other issues with the engine-----rich running or the like. If so, your CAT may be getting blocked. My CAT was almost totally blocked so I went to a salvage yard and found a good(totally clear) used OEM CAT for $150. But then, I gutted my old CAT(the front half, as the back half was clear) and reinstalled it until I can sort out if there is any other problem before I install my new used CAT. I gotta tell you that the car now performs like crazy. I cannot remember it having so much power. Of course it is throwing a CAT EFFICIENCY CODE. Da---yah---no cat at all.