Bubb
Newbie
Howdy all,
Long time lurker and fan of the site. I'm having a problem that's driving me crazy and am hoping the community can help. I've searched for this exact issue with no luck yet. Here goes:
The truck:
1995 Silverado K1500 ECSB Z71, 5.7, auto, 82k miles
I bought a year and a half ago from the original owner, who hadn't driven it in years
Been going through it and getting it in good running shape again, lots of recent work
The problem:
Had trouble starting when cold, so I took it to Oreilly's and swapped the battery after they confirmed it was bad. Immediately afterward it began surging/hunting for idle (never did this before). After a couple mins it found it's groove and I suspected the ECM just had to do some learning and would be fine. A few weeks later now it's still doing it.
These are the symptoms:
My thinking is that it's the IAC that's causing the hunting, but there's some other reason the ECM is commanding to IAC to do so. I don't have access to a tool that would allow me to monitor sensor readings from the OBDI ALDL while it is happening.
Long time lurker and fan of the site. I'm having a problem that's driving me crazy and am hoping the community can help. I've searched for this exact issue with no luck yet. Here goes:
The truck:
1995 Silverado K1500 ECSB Z71, 5.7, auto, 82k miles
I bought a year and a half ago from the original owner, who hadn't driven it in years
Been going through it and getting it in good running shape again, lots of recent work
The problem:
Had trouble starting when cold, so I took it to Oreilly's and swapped the battery after they confirmed it was bad. Immediately afterward it began surging/hunting for idle (never did this before). After a couple mins it found it's groove and I suspected the ECM just had to do some learning and would be fine. A few weeks later now it's still doing it.
These are the symptoms:
- Hunts for idle, varying rpm from ~500 to ~800 and will find a steady idle after ~15-30 oscillations, sometimes starts the hunt over again afterward
- Only happens in Park or Neutral, never happens in Drive or Reverse
- Only happens once it's warmed up (closed loop), seems to get worse the warmer it gets
- No driveability concerns other than maybe a rougher than normal idle, good power, good MPG, no CEL
- TPS, IAC, MAP sensor, CTS all seem good (and all replaced in the last year and a half)
- Fuel pressure is good at 13psi
- No vacuum leaks or other leaks (base of the TB, intake, etc) that I've been able to find
- Ran the procedure to reset IAC, didn't change anything
- I can get the hunting to go away if I spray carb cleaner down the TB but suspect that this is just masking the issue
My thinking is that it's the IAC that's causing the hunting, but there's some other reason the ECM is commanding to IAC to do so. I don't have access to a tool that would allow me to monitor sensor readings from the OBDI ALDL while it is happening.