Dear jd620,

Hope you're well. I gather you've cleaned the idle air control valve (IACV), without effect. For idle problems, that a first good step: it costs only some time, energy, and a little throttle body cleaner.

As the Engine Coolant Temperature (ECT) sensor "checks out" - resistance is within specification - I'd guess the problem is elsewhere.

Perhaps the root of the problem is inside the IACV, or between the wiring harness connector and the IACV's electrical connector. A faulty or corroded connection to, or inside of, the IACV creates resistance to current flow. Resistance creates heat. Thus, at start-up, the IACV works normally, and then - as the faulty connection heats-up - slowly goes "off spec".

I'd begin by cleaning the IACV's electrical contacts and those on its wiring harness connector. A spray corrosion remover, e.g., Deoxit, will dissolve any corrosion. This takes little time and costs little money.

If cleaning electrical connections does not yield a stable idle at 700-800 RPM, it's time to take a used, "known good" IACV, and replace the in-service unit. This swap takes only a few minutes. If the "used, known-good" IACV, keeps the idle at 700-800 RPM, problem solved. If not, then the IACV is "exonerated".

Before spending on replacement parts, I'm partial to cleaning electrical connections and using "used, known-good" parts to verify component status. The Bosch IACV is not cheap.

Hope this helps.

Yours faithfully,

Spook