What is causing this high idle? - Third Generation F-Body Message Boards

L695speed · 09-21-2009, 04:30 PM

I am trying to figure out why my car is idling at 1900-2100 rpms. Its a steady idle but it is obviously way too high. I have an L69 carb on an 87 LG4, since the car is an original L69 and I swapped a whole host of L69 parts from the original motor to this one its sort of a hybrid of the two motors. I didn't touch the wiring harness though.

So far I've replaced a bunch of the valves, (were stuck or old), ditched my smog pump as that siezed up, plugged my AIR tubing, plugged a couple other openings, no Cat converter, and the timing is good, idles smooth, has power, etc etc etc. So where the hell is the high idle coming from? I can't figure this out. I don't want to drive the car the way it is now. Previously it would die as I come to a stop. But it drives great. What am I missing here?

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novafirebirdguy · 09-21-2009, 05:50 PM

Dieing at idle would indicate a vacuum leak so I'd start there. Check the egr and all the rubber lines to the carb first.
Good luck
Alex

L695speed · 09-22-2009, 08:46 AM

I was thinking a vac leak too but every time I look at the vac lines chart on the emissions sticker every line is either hooked up or plugged up. The other problem I have is I don't think a vac leak will cause a 1000 rpm jump in idle. I had some of the vac leaks fixed by the local mechanic and he had it idling at 800. Since then, the heater core went. Before the heater core went I had it die a couple times coming to a stop. But when you fired it back up it would idle. Could it be carb related? That L69 carb I don't think has been touched since it left the factory, if it was touched it has at least 100,000 miles on it.

There is one vac leak, but it is for the air cleaner, and that alone should definitely not cause a 1000 rpm jump.

WSX123 · 09-22-2009, 10:43 AM

I had an 89 S10 that did the same thing before. high idle like yours

my motor was thinking it was cold outside, and was always trying to warm itself up.

I cant remember the name of the part. i believe it was a temp sensor. i took it to two mechanics and they didnt have a clue, the third one new right away without hooking it up to anything, fixed it right up.

L695speed · 09-22-2009, 10:47 AM

Quote:

Originally Posted by WSX123

I had an 89 S10 that did the same thing before. high idle like yours

my motor was thinking it was cold outside, and was always trying to warm itself up.

I cant remember the name of the part. i believe it was a temp sensor. i took it to two mechanics and they didnt have a clue, the third one new right away without hooking it up to anything, fixed it right up.

You mean the temp sensor on the thermostat housing? If thats the case then I think mine might be slightly damaged, when I installed the TVS Purge I noticed the temp sensor was not quite the way it was supposed to be.

WSX123 · 09-22-2009, 10:59 AM

that might be doing it then. its worth a shot, ecspecially if the part isnt much

L695speed · 09-22-2009, 12:30 PM

I also used to have a cold start switch on the car that was broken off, I thought that might be part of it but I was told by an older motor builder that it doesn't affect how the motor runs and starts, (told me it will start rich). The problem I have with the temp sensor is that is coolant, and coolant is always cold til it warms up. Thus I'm thinking it might not be the problem per say. I'm still thinking something in the carb itself.

L695speed · 09-24-2009, 01:59 PM

Ok, I thought I'd see if my choke would snap shut. With the air cleaner removed and a finger sealing up the vac line, I threw my choke wide open so my butterflies were vertical. Then I went back and moved the throttle like I blipped it and the choke butterflies snapped shut. Because of that I'm thinking the choke might be ok. I'd rather wait til I have some friends over before I try checking it with the car running.