I just finished changing the intake gaskets and water pump/thermostat on my '87 and now when i start it, it fires up and runs fine, but after about a minute the egr pipe starts lightly smoking. One thing to note was when it was apart the insulation on the pipe got destroyed and i replaced it with the aftermarket insulation. Then when it gets warm it starts idling rough and acting like it wants to die. I think the egr valve might be stuck closed but i wanted to see get a second opinion on it.

Thanks.

 

Sounds like the problem occurs when it enters closed-loop mode.
Have you checked for any stored codes?

By "EGR pipe" do you mean the pipe from exhaust manifold into the intake? If so at which end does it leak?

 

Please confirm this, but I think the EGR system, by design, is not used when the engine is at idle or wide-open-throttle. No exhaust gases are mixed with intake air during those times, by design.

There are some very knowledgeable people on this forum who can help walk you through this troubleshooting as long as you do what they tell you. I am still learning myself.

Do you have a Factory Service Manual for your year model?

 

The only time mine got hot enough to burn off the insulation was when the EGR was actually bad. This causes higher Combustion temperatures and can burn the insulation right off. A Faulty EGR is a real pain to fix but with time most people could do it.

The EGR valve is easy to test, simply add vacuum to the little hose fitting on it. When you apply vacuum the EGR valve should move and change the idle a bit. If it is not moving then you will need to replace it. The vacuum Solenoid that operates the EGR is a common failure point. After the vacuum stops moving the EGR diaphragm the parts likes to freeze up with carbon. The EGR Vacuum Solenoid is powered by a PWM signal. It needs vacuum and Power (PWM signal) for the solenoid to move the EGR diaphragm. I spent Days with wire brushes with Carbon Buster to get the passageways open again. If you take your time the engine can come out much better looking after all the work. I kept a couple cans of Spray Paint for the intake.

I would test the EGR and hope that it still moves okay. If not the parts are out there waiting for you and fairly easy to get still. This repair led to a major rework of the entire Intake system. The famous Snowballing effect of a simple project cost me a couple months and many dollars. I ended up with a new EGR Valve, EGR Vacuum Solenoid, fuel injectors, Fuel pressure regulator diaphragm, Plugs, wires, 9th injector (Cold Start Injector), and dozens of gaskets.

 

I believe you can test the EGR valve by sucking on the vacuum line that goes to it - you should hear the diaphragm moving back and forth. I think there's also a small plastic check valve that can break and prevent the EGR valve from getting vacuum.

Just spitballing, but an exhaust leak could be forming when things get hot, causing air to get sucked in. When the oxygen sensor sees this fresh air, it would add fuel and cause the car to run rich.

 

Corvettes with faulty EGR Valves tend to run higher than normal Combustion Chamber temperatures and periodically this leads to pinging or detonation under loads. They can get the EGR parts carbonized very quickly. If you get your Corvette Emission Tested it would show up as a very High NOX which is a byproduct of the EGR having failed.


The Oxygen Sensor also plays a HUGE part in the General everyday running of the Corvette's Engine. They were designed to fail "Rich" to prevent hurting your engine,this is smart otherwise a defective 02 could toast your engine by running it too lean. Fortunately O2's fail "Rich" and their signal width starts to narrow and then it starts slowing down which is potentially less "accurate". The engine needs an accurate Oxygen sensor to get the most out of the fuel you are feeding the engine. If the Oxygen Sensor is over 24 months old or has over 50 k miles in your L98 equipped C4 I would replace it, as GM instructed.

It is really good to do as well as important to the earlier "single wire" (non-Heated) Oxygen Sensors, but not the later "Heated style" (multi wire) which are capable of much longer runs before needing to be replaced. The 24 months applies to L98 engines with "Single-Wire" Oxygen Sensors like my 1988 C4 was equipped with. I use a new one every 2 years, They might still be functional at this point but I want the most out of my L98 as it really helps the economy not to mention performance. An older Oxygen Sensor that has failed tends to cause the engine to run rich and this can lead to catalytic converters getting plugged