1994 GMC Sierra K2500 w/ 7.4L.
It had been serviced thoroughly a couple years ago with new distributor, new plugs and wires, and a bunch of other things I don't remember anymore.
It runs well once it's warmed up, but on a cold start, it will idle high for a bit like normal, and then when it drops down to low idle kind of suddenly (is that normal?), it starts fluctuating and getting close to stalling, and then it catches itself and revs up again (presumably this is the IAC doing its job).
It does this for a few minutes, and then it stabilizes once it gets up to normal operating temps, at which point it's fine.
It seems to do this in any weather, but it's more pronounced when it's cold (which, in California, isn't saying much ).
The ECU died back in early 2020, at which time I bought a replacement (I transferred the CALPAK, which seems to work at least as well as it did before the ECU conked out, so I assume it's still good?). Could this have anything to do with it? I seem to remember that that was about when the weird idling on cold starts began, but I'm not totally sure. Could the replacement ECU be faulty somehow?
A possible clue to that effect is that the SES indicator will sometimes light up briefly during the rough idling episodes (it will go out when the idle evens out). I don't know the code.
Thanks!
c
It had been serviced thoroughly a couple years ago with new distributor, new plugs and wires, and a bunch of other things I don't remember anymore.
It runs well once it's warmed up, but on a cold start, it will idle high for a bit like normal, and then when it drops down to low idle kind of suddenly (is that normal?), it starts fluctuating and getting close to stalling, and then it catches itself and revs up again (presumably this is the IAC doing its job).
It does this for a few minutes, and then it stabilizes once it gets up to normal operating temps, at which point it's fine.
It seems to do this in any weather, but it's more pronounced when it's cold (which, in California, isn't saying much ).
The ECU died back in early 2020, at which time I bought a replacement (I transferred the CALPAK, which seems to work at least as well as it did before the ECU conked out, so I assume it's still good?). Could this have anything to do with it? I seem to remember that that was about when the weird idling on cold starts began, but I'm not totally sure. Could the replacement ECU be faulty somehow?
A possible clue to that effect is that the SES indicator will sometimes light up briefly during the rough idling episodes (it will go out when the idle evens out). I don't know the code.
Thanks!
c
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