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EGR Valve



My Vette's L-48 engine was rebuilt to stock in '93. There was just one problem: a rough idle. The mechanic did something odd to the carb to solve the problem - he plugged several tubes in the bottom of the carb with silicon. The rough idle disappeared. By the way, he left the EGR valve disconnected.

Fast forward to today. I drove my Vette very little until this year and discovered that it got terrible gas mileage - between 6.5 and 10 miles per gallon. I had my mechanic (a new one) look into the problem.

There didn't appear to be any gas leaks and the fuel pump looked o-kay. So my mechanic rebuilt the carb. When he saw the silicon he was very puzzled - he'd never heard of this before. He removed all the silicon and put the carb back together. The car now works great - in fact, it has more power and acceleration than it ever did before. However, I now have the original problem: a rough idle. The EGR valve, by the way, he still left disconnected.

I turned to this forum for an answer and found that others have had similar troubles. The solution was to replace the EGR valve. I connected mine (but haven't yet told my mechanic) and most of the problem went away.

My mechanic believes that the problem is still in the carb - that the lower plate of the carb might still have a plugged tube or two and need replacing. He doesn't believe that the EGR valve has anything to do with the problem. Having connected the EGR valve and seen most of the problem vanish I have my doubts.

Is the problem the EGR valve or the carb?

The EGR valve, by the way, is incorrect for my car, a L-48, nor is it correct for a L-82. (Could this explain the remaining problem?) My engine, I've recently learned, is not entirely L-48 - it has a carb from a 1980, for instance, and its valve covers are L-82. Who knows what else is incorrect. I can't check right now because the old rebuild bills are temporarily inaccessible.

How can I determine what EGR valve to use on my Vette?

Some people disconnect the egr diaphram but do not plug all the egr hoses from the egr valve in the intake, this could be the case if you just hooked up the egr and it ran fine.

Your car should idle ruffer when the egr system is in place and all items work.

Check your egr to see if it is working, by giving the car gas and watching the egr diaphram. If it moves up as you turn the throttle it is working. You can also push the diaphram in the egr housing up with 2 fingers, it should move with a little effort. If not your egr is not working and might need cleaning. These things carbon up something nasty.

I would get my egr system working properly and then have it tuned, if you plan on running egr.

I would plug all the egr lines and get the engine tuned if not running egr.

EGR does put a drain on the engine and will alter your idle drasticly enough to cause ruff idle.

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