Uneven Idle
 

I notice that the idle on my 83 SL380 seems to surge. All of a sudden the idle seems to increase a few hundred rpm then comes back down. It keeps doing this. Any thoughts on where to start?

uneven idle
 

buried behind the glove box is the expensive relay that runs the idle valve.what you are seeing are common warning signs that relay about to bite the dust.it can be had from programa as a rebuilt on an exchange basis[to ease the sticker shock] good luck david poole dallas tx.

83 380sl Idle
 

At pin 9 of the idle speed control unit is input for a/c compressor engagement,Every time the a/c clutch engages the idle is raised.
Make sure you don't "fix" a normal condition.
Mike

How much does one of these cost and what happens when it finally bites the dust? Will the car just die on the road?

Thanks