dwb
Proven Member
- 844
- 596
- Sep 9, 2021
-
Broomfield,
Colorado
I'm testing out a stock 1g ECU (1993 EPROM) and discovered it has no idle control. I know it's the ECU since my original ECU works fine. It doesn't fast idle on startup, compensate for any electrical load, nor does it compensate if I turn the AC on. My logger shows the ISC steps moving, but no change in idle speed. It eventually pegs at 0 or 120 steps.
I have no prior knowledge of the condition of the ECU. The board is all original with no repairs. Capacitors were original and showed obvious signs of leakage, so I replaced those before testing it. I cleaned up the corrosion as best I could and nothing seemed obviously damaged. I do still see some corrosion up underneath the heatsink, in the general area of the four ISC pins. I still need to remove the heatsink to gain access to that area to clean/trace the circuit and inspect for broken traces.
I've heard of two ways an ECU can lose the idle circuit - either a malfunctioning ISC or corrosion. Either one could be a possibility. If it were caused by the ISC, what components would I be looking to replace? Any other tips on fixing this ECU?
I'm pretty competent when it comes to soldering and electronics repair, but not so much at diagnosing without just throwing parts at it. I'd like to avoid sending for repair, but always an option if this goes above my head.
I have no prior knowledge of the condition of the ECU. The board is all original with no repairs. Capacitors were original and showed obvious signs of leakage, so I replaced those before testing it. I cleaned up the corrosion as best I could and nothing seemed obviously damaged. I do still see some corrosion up underneath the heatsink, in the general area of the four ISC pins. I still need to remove the heatsink to gain access to that area to clean/trace the circuit and inspect for broken traces.
I've heard of two ways an ECU can lose the idle circuit - either a malfunctioning ISC or corrosion. Either one could be a possibility. If it were caused by the ISC, what components would I be looking to replace? Any other tips on fixing this ECU?
I'm pretty competent when it comes to soldering and electronics repair, but not so much at diagnosing without just throwing parts at it. I'd like to avoid sending for repair, but always an option if this goes above my head.
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