I have the 1FZ EF engine. I have read about the Seafoam. So people use a funnel to force in Seafoam? I have always think about that. Have you try this stuff in your gas tank?

Possibly an EGR valve stuck open or not sealing when closed?

That should throw a code with the check engine light? What gets me is there is no check engine light. I am still thinking its something simple but just can't think of anything else.

It might throw a code but might not. It didn't on my obd1 Mazda. I diagnosed it by cutting a gasket which covered the EGR hole blocking any flow. My idle improved dramatically.

If I understand the CEL on OBDI cars, it only comes on in dire circumstances. It is not a sign to pull out your code reader. It's a sign to check the basics, like coolant.

A stuck smog valve would be a culprit as hardflex said.

Before dumping Seafoam in the thing, think about the cat. Better to find the problem directly, IMHO, of course.

EarlyPorsche, sorry, bad mood.

I depends on what sort of miss you have. EGR leak is sort of a weakening of firing, almost like it's running out of gas. Not a regular miss that a fouled plug or bad wire/injector would produce.

Common test of EGR is to apply a vacuum to the vacuum port on the EGR while idling. If the engine starts to die it's working. If it's leaking it's dieing on a smaller scale.

Unhook a vacuum hose (brake booster is biggest diameter) to the intake manifold and stick it in the open can and it will draw it out of the can and into the intake

It works well in the gas tank, but that's a completely different system getting cleaned