1992 Corvette LT1 Low idle speed?
Thread Starter
Intermediate
Joined: May 2015
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From: Philadelphia PA
1992 Corvette LT1 Low idle speed?
I picked up a '92 lt1 Auto with 68k miles on it recently and I am noticing the idle is lower than other cars that I own. I had the ecm rebuilt because it crashed 2 days after I bought it 
Now I am noticing that the idle is steady at 500-550 rpm in drive when it is fully warmed up. It stays smooth right at 500 at a stop and does not feel like it is going to stall at traffic lights, it just feels too low(maybe the muffler eliminaters make it sound off, like it's gonna stall). The car also runs about 215°-225° fully warmed up on a 80° day in city traffic with the AC off. So is this idle speed and temp normal for a 92?
Now I am noticing that the idle is steady at 500-550 rpm in drive when it is fully warmed up. It stays smooth right at 500 at a stop and does not feel like it is going to stall at traffic lights, it just feels too low(maybe the muffler eliminaters make it sound off, like it's gonna stall). The car also runs about 215°-225° fully warmed up on a 80° day in city traffic with the AC off. So is this idle speed and temp normal for a 92?
Drifting
Joined: Sep 2014
Posts: 1,579
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From: Trieste Italy
I picked up a '92 lt1 Auto with 68k miles on it recently and I am noticing the idle is lower than other cars that I own. I had the ecm rebuilt because it crashed 2 days after I bought it Now I am noticing that the idle is steady at 500-550 rpm in drive when it is fully warmed up. It stays smooth right at 500 at a stop and does not feel like it is going to stall at traffic lights, it just feels too low(maybe the muffler eliminaters make it sound off, like it's gonna stall). The car also runs about 215°-225° fully warmed up on a 80° day in city traffic with the AC off. So is this idle speed and temp normal for a 92?
Now I am noticing that the idle is steady at 500-550 rpm in drive when it is fully warmed up. It stays smooth right at 500 at a stop and does not feel like it is going to stall at traffic lights, it just feels too low(maybe the muffler eliminaters make it sound off, like it's gonna stall). The car also runs about 215°-225° fully warmed up on a 80° day in city traffic with the AC off. So is this idle speed and temp normal for a 92?
Thread Starter
Intermediate
Joined: May 2015
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From: Philadelphia PA
I'm gonna clean the TB. I mean The car has never stalled or stumbled , but sitting at a light when its around 500-50 is a bit scary. You can really hear it drop down because its got eliminators. Maybe its normal and I'm making a big deal out of it?
Drifting
Joined: Sep 2014
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From: Trieste Italy
I've a 1995 manual, ZF. I was on opposite situation than your: high idle, I've tried to do a lot of things without result, clean TB, replacing IAC, try to set TPS, no result. Finally I've pulled it down with screw, its work.
I've readed somewhere, don't remember where, corvette with AT should have idle little bit lower than corvette MT, so mine is about 850-900 your should be 800-850
Last edited by Christi@n; Sep 3, 2015 at 11:25 AM.
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Drifting
Joined: Sep 2014
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From: Trieste Italy
Cap is in place in order to not permit to touch screw...
Last edited by Christi@n; Sep 3, 2015 at 02:18 PM.
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On my 92, I had a number of seemingly unrelated symptoms, including low or high idle. In my case it turned out to be the ECM, and a rebuild fixed all those issues.
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From: Philadelphia PA
Drifting
Joined: Sep 2014
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From: Trieste Italy
Not in front of my FSM right now, but IIRC, the throttle position sensor and the IAC work together to set the idle. Messing with a screw that is not intended be be adjusted (hence the cap) is asking for other problems. Find the real reason for the low idle, and then deal with that.
On my 92, I had a number of seemingly unrelated symptoms, including low or high idle. In my case it turned out to be the ECM, and a rebuild fixed all those issues.
On my 92, I had a number of seemingly unrelated symptoms, including low or high idle. In my case it turned out to be the ECM, and a rebuild fixed all those issues.
Thread Starter
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Joined: May 2015
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From: Philadelphia PA
The vette has been broken for quite a while. And with the PA winter I didn't drive it much. But now I got it back up and running again with a new opti and injectors. I have cleaned the TB and IAC with cleaner, wiped it down, and it still runs at 550rpm? What now?
Team Owner
Joined: Jul 2004
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From: Hartford WI
Now you get a scanner that can read the ECM and see what the command idle is for the given conditions. Also you can see what the RPM reading is and not what the tach, which is often inaccurate says.
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From: Bowling Green Ohio
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Not in front of my FSM right now, but IIRC, the throttle position sensor and the IAC work together to set the idle. Messing with a screw that is not intended be be adjusted (hence the cap) is asking for other problems. Find the real reason for the low idle, and then deal with that.
On my 92, I had a number of seemingly unrelated symptoms, including low or high idle. In my case it turned out to be the ECM, and a rebuild fixed all those issues.
On my 92, I had a number of seemingly unrelated symptoms, including low or high idle. In my case it turned out to be the ECM, and a rebuild fixed all those issues.
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From: Anaheim CA
I had problems with the engine stalling when I came to a stop. I drove with one foot on the brake and the other on the accelerator so I could catch it and keep the RPMs up. I did a minimum idle adjustment (had to remove the plug) and everything has been fine for the last few years.
I think the linkage bends over time and goes out of adjustment. Plus I see that the idle screw made a slight depression in the throttle linkage tab, which would throw it out of adjustment:
I think the linkage bends over time and goes out of adjustment. Plus I see that the idle screw made a slight depression in the throttle linkage tab, which would throw it out of adjustment:
Last edited by Cliff Harris; May 18, 2016 at 11:55 PM.