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The c4vettes.com site indicates that with this error code, the EGR "switch" should be replaced first. Where is it on my 88 coupe?????? I see an EGR valve, EGR solenoid, no EGR switch.
The EGR feed tube is where the switch is mounted on back of the manifold on the passenger side.
The switch is a black wire with a white ceramic looking housing.See if thats broken up or wiggled loose.
Sometimes the code will appear on startup and stay there, sometimes it won't show at all, sometimes it will come on while driving. Great answer huh? :) Now that I know where it is I will check it out. There is something definitely wrong with my EGR system, I have issues with rich gas smell periodically coming from up front.
If you end up replacing the EGR switch, here is a suggestion to consider. Leave the old pig tail connected and cut the wire near the old EGR switch. Cut the pig tail connector off the new one, splice, solder, and use some heat shrink to complete the connection. Unless you have really small hands, it's difficult to get in there by the distributor to disconnect and re-connect the new pig tail connector.
Both the switch and the valve are relatively expensive so I suggest you use the test scheme to try and isolate the problem.
If the switch is shorted closed (you might check it's wire for a bare spot) you will always get the code at start up; if it is locked open you will always get the code after cruzin for a few minutes if the engine is warm enough (i.e. > 176deg F). Check for a + voltage on the switch at start up; if zero the switch is shorted or stuck closed.
Since it also comes on after driving, it sounds to me like the valve is sticking, sometimes open and sometimes closed.
Go to 65ZO1's web site, he lays it out for you on how to test it. Mine ended up being the switch which was about $8 and it is a pain to get to the connector, but it is possible without removing the distributor. If the switch does not close after 4 minutes of EGR comand and the coolant temperature being over 176, the light comes on. Mine never came on till i replaced the t-stat, then it came on 4 minutes down the highway. But seriously, 65ZO1's website lays it all out for you.