EGR valve on 93 Sonoma

My Sonoma will start running and idling rough after it warms up. If I tap on the egr valve it smooths out for a while then starts running rough again.
I replaced the egr valve with a new one but the problem has stayed the same. What is controlling this and why would tapping on it provide a temporay fix?

Welcome to AF
What engine?
Vacuum or electric controlled EGR valve?
Is it getting carbon balls sticking the end of plunger?

4.3 engine with electronic controlled EGR valve.
I repleced with new one but the problem stays the same.

4.3 engine with electronic controlled EGR valve.
I repleced with new one but the problem stays the same.

Is it setting and codes or check engine lights?
I would pull it off and check for carbon or carbon balls under plunger.
Also check the wiring on the wire plug in.

The only thing I haven't cecked is the wiring harness which may be the problem since a tap will correct the problem for a while.
Will bypassing the ERG completely witk a solid plate hurt anything?

The only thing I haven't cecked is the wiring harness which may be the problem since a tap will correct the problem for a while.
Will bypassing the ERG completely witk a solid plate hurt anything?

In the long run it will damage engine and lower gas mileage.
Best to fix the problem.
Any check engine lights?
Any carbon under egr valve plunger?

The check engine light only comes on when it starts running ruogh. When I shut off the engine and tap the EGR it straights itself out ahend the light wull go off. This is a new OEM egr that I replaced the other one with so there are no carbon deposits anywhere.

But you still may have some more carbon balls under plunger.
I have had a lot of them go threw the carbon ball making route.
Sometimes bad engine running or tune up tends to make more than there share of carbon balls..
Get the code no and post back no and remove and recheck egr valve when it is acting up.
If a carbon ball problem they make a screened gasket that helps.

Thanks for the help. I will pull it off one more time and check/clean. I don't think this is the problem. I still think it is in the relay to the egr valve.
I will have to trace it to see where it comes from and then check to see what turns it on and off.

When you talk about the plunger and checking under it are you talking about the small hole with the screw? If so how do you check under it?

Thanks for the help. I will pull it off one more time and check/clean. I don't think this is the problem. I still think it is in the relay to the egr valve.
I will have to trace it to see where it comes from and then check to see what turns it on and off.

No relay on it.
It is computer controlled and monitored.
A good engine capable scanner will test it and tell you what the problem is.
The code will also point to the problem.

When you talk about the plunger and checking under it are you talking about the small hole with the screw? If so how do you check under it?
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A good eyeball on it or blow or suck on it and see if the plunger seat is holding.
If it has a carbon ball under plunger you will see it.
MT