Can running lean cause damage?

[jzbeaver]

My 98 Windstar 3.8 is running lean because of a failed IMRC, which I am
ordering. In the meaintime, I plugged the hose, but I am wondering if
running lean can cause anything else to deteriorate or fail-- and if it also
will be running hotter?

[PBZX3]

Running lean will cause higher EGT's (exhaust gas temp) but the cooling system should be able to handle the extra heat generated during combustion. The only other thing with a lean condition is pre detonation of the fuel air mixture. This can cause pinging under higher load conditions. I would certainly have the radio off and listen for pinging until you get it fixed. If pinging occurs you can change to a lower gear or let off the gas peddle.

[jzbeaver]

Thanks for this info, PBZ. I have the part and will be installing it shortly.

Someone else-- not on the forum-- thought that running lean would eventually
damage the catalytic converter. Do you know it that is accurate-- and if so,
would that be as a result of the exhaust being hotter?

[PBZX3]

Too rich can ruin the cat. Lean should not be a problem. Cats like heat.

[wiswind]

I have not done it, but it has been posted, and makes a lot of sense.
You can block the IMRC in the closed position.
They are held OPEN by springs.
Vaccum that is present when the engine is running pulls them closed.
Carefully pulling them closed and blocking them in that position will have them in the normal position for most driving conditions.
I do not think that your vehicle is running lean.
The PCM is putting the correct fuel in to match the air that is flowing into the manifold, regardless of the IMRC being open or closed.
However, a leaking vaccum diaphram inside the defective actuator (usualy only 1 of the 2 actuators is defective, robbing the other of the vaccum) would give you a vaccum leak, which could cause you to have a lean code.
As you have disconnected, and plugged the vaccum line that drives the IMRC actuators, you have taken care of the vaccum leak.

More air being available to the cylinders, caused by the open IMR could cause some drivability issues, but not an overall lean condition (as in all the time).