Valve Cover Grommet Replacement
A commonly overlooked maintenance item on older Corvettes is the valve cover grommet for the PCV valve and the “breather” port. (See Photos for location of these grommets on my 1988 L98.) These rubber grommets, like all rubber components dry out and harden over the years, particularly in the hot, under hood environment. As they shrink and lose elasticity, the seal for the PCV Valve and breather connection is compromised. This allows leakage around these components, causing a loss of vacuum that can lead to a rough idle and other symptoms typical of an engine vacuum leak.
The fix is inexpensive and takes about five minutes.
Be sure to purchase the correct size grommets for your particular engine. A purist, I got mine at a Chevy Dealer for less than $6.00 for the pair, but they are available from aftermarket suppliers at any well-stocked auto parts store. This is also a good time to inspect and replace the PCV and breather hoses if necessary. My hoses were fine so I did not replace them. Before the trip to the parts store check to see if you need a new PCV valve too. With the engine at idle, pull the PCV valve and put a finger over the end to check for suction. Shake the PCV valve and listen for a clicking sound. If it fails either test, replace it.
Remove the beather connector and the PCV Valve (if your grommets are as bad as mine were the PCV valve will very easily lift out of the grommet).
Carefully use a screw driver blade or other suitable tool to pry the old grommet out of the valve cover.
Clean the hole of any debris, being careful not to push crumbled rubber particles into the valve cover.
Wipe the area clean and then simply wedge the new grommet into the hole in the valve cover being sure to align the taper into the correct position – don’t push too hard and lose the grommet inside the valve cover!
Reinstall the PCV valve and the breather connector for a good tight fit.
This simple fix immediately smoothed out the rough idle on my C4