2003 Toyota Solara. V6. Engine revs to about 2500 rpm, slows to 1500 rpm, then right back up to 2500. Up and down repeatedly. When in gear the rpm is about 2100 continuously
The problem might be with the Idle Air Control/Air By-Pass motor circuit.
This device is mounted mounted on the throttle body. And it controls the engine idle speed anytime the accelerator is released. If this device malfunctions, it can either cause an erratic idle speed or it can cause the engine to stall when off the accelerator.
Also, check the vacuum hoses for leaks. A vacuum leak anywhere on the intake side will cause this problem.
Vacuum leak can also happen where the intake manifold attaches to the head, though I would not expect that yet on an 03 Toyota.
On a lot of V6 engines the upper plenum attaches to the intake manifold. There is a gasket that seals these two together. If this gasket breaks it can let enough air in to cause the high idle. If you have a way to listen for an air leak run the tube around that joint and see if you can see or feel the air entering.
This gasket does not take a lot of labor to replace.
Thanks for your input. The auto repair shop replaced the Automatic [or Adaptive] Idle Control vavle asembly. It was my “second opinion” so I could gauge if the shop was on the right track. I appreciate you taking the time to respond.