All the threads I've read about rough idleing lead me to think my EGR valve is bad, or dirty, or something completely different...

Symptoms:
Rough idle.
Runs rough at low rpm's under load.
Smooths out during higher rpm's and coasting.
Engine temperature makes no difference.
Fuel economy has gone to pot (from 20.5 to 15.XX)
Performance has suffered slightly.
Seems like engine runs louder (like an exhaust manifold leak, but could be my imagination).
Occured literally overnight.
No Codes.
I have replaced the plugs, wires, cap, fuel filter, as well as several cans of fuel system treatment. All to no avail.

If not the EGR valve I am leaning to a leaky injector.

Car is a 93 Sedan deVille 4.9 with 160K in the ticker. Any helpis appreciated, also if additional informationis needed I will be hapy to provide it.

Thanks,
Andrew

First clean the EGR tubes in the TB. If that does not help, then pull and clean the EGR pintle valve.

how do you clean the EGR?

I am going to try cleaning the tubes tonight, maybe the valve too if need be, I'll post my results.

To clean the tubes I am going to pull the air intake, prop the throttle plate open and run a gun cleaning brush down the tubes... Hopefully I won't have to experiment with cleaning the valve.

how do you clean the EGR?
Go to the Tech Tips section. There is a "How To" posted there.

Well... That was an ordeal, I cleaned out the tubes with no success or change in the condition. So I went ahead and pulled the EGR Valve, cleaned out and put everything back together. It still idles poorly, but more of a definate sputter, especially at idle. I have not had a chance to drive it yet but I bet that the condition will persist. I am going to read that tech article once more to see if I might have missed anything.

Given my little success I started turning off individual injectors, I could tell when all injectors went off except for number 2. So it begs the question of what are the symptoms of a leaking or faulty injector?

I had a similar problem with my 88 deville, it has an injected Throttle Body by 2 injectors... one of the injectors would not work on occaision, then got to the point where it would not work at all, no codes, turned out to be the ECM (computer), picked up one from the salvage yard and have had no problems since. just a thought.

How did you determine one injector wasn't shooting?

Also I have driven more now and the condition is much the same, under light throttle the car shakes/vibrates due to the engine running so rough, giving it more throttle will increase the situation until at certain point higher in the rpm range it instantly clears and accelerates as normal. WOT has suffered though not as badly as off the line, mid range seems to be only slightly down...

I think I will try replacing the EGR solenoid, valve, and possibly the FPR. Replcaing to much more will start getting pricey especially when I'm not exactly sure what will cure it. I've read all the osts on rough idleing and the ones that were similar to my situation seem to go in this direction, with no definative solution. Injectors will be my last ditch. Am I still on the right track with what is wrong with it or could it be something different or...

Many thanks for all the help thus far.

The fuel pressure regulator is the first thing I would suspect with your symptoms.

With the engine idling pull the vacuum line off the FPR and check for the presence of fuel in the line or leaking from the vacuum nipple on the FPR.

If you disconnected injectors one at a time or turned them off one at a time and could isolate one that didn't seem to respond when turning it off then possibly that injector is sticking open...?? You can investigate further by removing the four bolts in the fuel rail hold down and lifting the rail up enough that the injectors are clear of the ports in the intake that they nest in. Turn on the key without cranking (to prime the fuel system) and watch the injectors for drips and leaking. If one leaks then replace that injector. Just slide the injectors back into their ports (a little engine oil on the o-rings helps them slide into place) and reinstall the rail holdowns.

Will do at lunch, be my luck that's it, and another impossible to reach bolt... *&^#$%...

I got to thinking and I am using the FDC to record my loss of MPG, so sense the FDC gathers its information by the signalled injector pulse width, the the car "knows" it is using more fuel, meaning it isn't leaking through an injector or FPR. (I checked it just now, no fuel in the line nor do I have trouble with hot starts.) This points me a little back to the EGR system, the valve seems to be opening and closing fine by hand so maybe the solenoid is stuck commanding it open at all times. I am replacing the valve tonight and possibly the solenoid as well. Does this sound right? Or should I look at something else?

Thanks, guys for the help, I really appreciate (and need) it!

***EDIT***
I have now replaced the EGR Valve, no improvement... I checked some more of the PCM Data through the OBD, I still notice no effect by turning off injector number 2, I looked at all the other readings and while I don't know what normal is none of them were fluctuating wildly. the ingine idle speed goes between 630-750 rpms, I could not override the injector flow (8.8.8) to test injector 2. One thing I am concerned with is the Block Learn is at 125 counts, fuel system is too rich and delivery is reduced... This is really starting to look like a fuel delivery issue and not EGR at all. Any further suggestions... Or help?

Follow Up:
After rplacing all the EGR components I regrettably replaced spark plug wires (cheaper than injectors plus disabling injector 2 resulted in no change of idle quality along with the definate putt, putt, putt at the tail pipe I was feeling cylinder 2 was having issues be it plug, wire or injector) problem solved, mostly. Mileage is back up to only 19.5(6)ish, which is down almost exactly 1mpg. I am thinking of checking the O2 sensor readings, Specifically the one downstream of cylinder 2 and comparing it to readings from the opposite sensor. I am thinking sense so much unburnt fuel went through that cylinder that the sensor could be having problems, catalytic convertor might not be happy about that or the plug maybe fouled...
My knuckles have almost healed so I will be back at it shortly...:want:

94 DeVille 4.9 Same problem...Lots of noise from Catalytic converter during the rough idle. Unplugging the vacuum supply to EGR causes engine to run silky as normal. Milleage drops to the loss of EGR function..with it plugged up MPG goes up. Ex: 0 - 30 mph = 1-3 instant fuel econ...with EGR unplugged. With the vacuum connected: about 7 mpg instant avg 0-30 mpg. I have been reading the Cadilac shop manual for months trying to figure out if the EGR solenoid is energized during idle. The description of the system is to allow exhaust to flow back through the intake to keep combustion temps down during moderate through WOT opertaion. The result of EGR is loss of power with a plus side being lowering cheamber temp. Cadillac has solved this balancing act in Northstar by implementing a vaiable position EGR (bet THAT costs a penny!). Anyway, one side of the solenoid is designed to be hot at all times...the PCM can energize the solenoid by grounding the other wire at its desretion. SO>>>I think the thing shouldnt be on at idle...sounds like crap...like a have some sockets in my catalytic converter..but with it unplugged...smooth as silk...Anybody solve this problem yet?

94 DeVille 4.9 Same problem...Lots of noise from Catalytic converter during the rough idle. Unplugging the vacuum supply to EGR causes engine to run silky as normal. Milleage drops to the loss of EGR function..with it plugged up MPG goes up. Ex: 0 - 30 mph = 1-3 instant fuel econ...with EGR unplugged. With the vacuum connected: about 7 mpg instant avg 0-30 mpg. I have been reading the Cadilac shop manual for months trying to figure out if the EGR solenoid is energized during idle. The description of the system is to allow exhaust to flow back through the intake to keep combustion temps down during moderate through WOT opertaion. The result of EGR is loss of power with a plus side being lowering cheamber temp. Cadillac has solved this balancing act in Northstar by implementing a vaiable position EGR (bet THAT costs a penny!). Anyway, one side of the solenoid is designed to be hot at all times...the PCM can energize the solenoid by grounding the other wire at its desretion. SO>>>I think the thing shouldnt be on at idle...sounds like crap...like a have some sockets in my catalytic converter..but with it unplugged...smooth as silk...Anybody solve this problem yet?

The EGR solenoid is not energized in N and P, so there is no vacuum supply to EGR valve and it is supposed to be closed.

Hi,

Have a similar problem with my Devile -91. Rough idling with low power at low rpm. I have replaced the EGR Valvue, but that was before when I had to replace the PCM... that's another story...

Anyway, I belive that the EGR vacum solenoid should rattle when shaking it? Mine doesn't. Further more I have ok fuel pressure, new cables etc.

Comments?