1992 Gmc Safari mini van idles high then normal, What might be causing this issue?
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Any Check Engine lights on??? Could possibly be a heated oxygen sensor acting screwy or the catalytic converter giving bogus info since it runs fine at first. I know at cold start, the ECM/PCM ignores the oxygen sensors until it sees a closed loop, may need to take to a shop & have someone look at the data with a scan tool. Would have said a vacuum leak but you said runs fine at 5-10 minutes which a vacuum leak will run high at startup.