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Rough, high idle

Mar 26, 2002
Midlothian, VA
1981 white/blue interior automatic
I have quite an odd problem with my '81 automatic. After driving it for about 20 miles in light traffic it gets a very rough, high sort of idle. It has been doing this for quite sometime (since summer), but it was very rough today; allow me to elaborate. When I slow down from normal driving speed (45mph) to a stoplight the whole car seems to shake, and I notice that the rpm is about 750, in gear, and almost 1000 rpm in neutral! Wwhen I start to move again it smoothes out just fine, but you can tell that it wants to keep moving all the time, example- almost like the throttle is stuck open a tiny bit... when cruising the only difference i notice is it doesnt loose speed as fast.. it seems like the engine is still pulling... like im tapping the pedal a tiny bit, though im not. This problem goes away after the car has been sitting overnight, regardless if the fast idle comes on because of cooler temperatures. Could all this be related to my tcc selenoid problem in my tranny? It started around the same time... why does it happen only after I drive it for a while? I dont think I could fix this problem myself since my mechanical inclination of cars is low, and I only have basic hand tools, but I would like to know if I should bring it in to my vette mechanic or just live with the problem? Besides the shaking at idle there is no problem, and I dont mind the shaking that much, just worries me.. thanks for everyones help in advance and sorry for the long post.


Check voltage to your electric choke. If you loose voltage, then the choke will tend to remain engaged. It should read 12 -14 volts. Without the voltage the heating element will not get the juice required to allow the choke to disengage...

Check your choke wire to make certain that you have power when the key is on. If you do then one of two problems exist.
1. your choke coil is burned out and needs to be replaced
2. or you are losing the ground to your choke coil

You might try running a seperate ground wire from the choke housing to a carb or mainfold bolt. Make sure to get the connections clean. If the ground wire does not cure your problem, replace the electric choke coil with a new one.
DDL-81, GerryLp,

Im sorry for the delay in response, ive been very busy, and now ive come down with the flu, but I wanted to tell you what ive come up with so to show you that your information and time have been much appreciated. I pulled the choke wire, and then turned the key on to the "on" position, before cold starting it for the day. I noticed that a piece of the choke wire connecter had broken off in the choke assembly, but I eventually fiddled with it till I got it out. The contacts still seem to be in good order though, and the plastic piece that was broken off hopefully shouldnt effect the electric contact at all... just how it seats. Now, I couldnt get any volt readings at either the choke wire, or at the choke assembly itself.. but I got a very high ohm reading.. which leads me to believe that i wasnt getting a good contact? they didnt appear to be corroded in the least, but I could be wrong.. also the voltmeter I had was rather cheap, and maybe that was the problem. I searched online for replacement choke coils for the '81 E4ME but couldnt come up with anything, the replacement seems pretty straight forward in my repair manual and if its rather inexpensive i think id just like to replace it... anyways Ill give it another try later when I get better, ill get some help too this time... ill keep you all posted, thanks again for your time and knowledge.


You need to see 12 volts on your choke wire with the key on. Remember, that 1 lead of your tester is in the choke wire, and the other to ground with your tester on DC volts. If you have no voltage then there is your problem. Check to see if you have a blown fuse. If not you can try to chase it back into the harness to find the break in the wire, or just find another 12 volt power source that is switched with the ignition and run a new wire. There should be a high resitance reading on your coil if it is intact, it is a resitance heating coil that turns nearly red hot when energized. The replacement choke coil, should you need one, should be available from NAPA or Autozone or the like. If yours is original, then you will need to carefully drill out the aluminum rivets and replace them with the self tapping screws provided with the electric choke kit.
DDL and Tatortot,

I believe that the engine must be running when checking for voltage at the choke lead. I get no reading when ONLY the key is turned to the "ON" position. I normally get 13 to 14 volts with the engine running.

In the world according to Gerry (inside my head...:L) this makes sense, for if the choke lead was live with just the key in the on position, then the heater core would begin to heat and shorten the time amount the engine is at fast idle to warm-up in cold mornings (once you kick the gas pedal to bring the engine back to idle). Besides, the lead wire comes from the alternator, if my memory serves me correctly...Do I make sense?
Wow, thanks gerry, you just cleared up all my questions. I was able to test the choke wire again today and this time I got 12 volts, but no reading at the choke itself. I guess that answers my question of why no reading. So... any other ideas at what my problem may be? Still bad coil maybe? Im dropping by the mechanic tomarrow and Im gonna ask him if he has any ideas. Thanks for all your help everyone.

Sorry its been a while since ive posted, its been busy around here cause of the holidays. I talked to my vette mechanic and he says it is "definatly a choke problem". He believes that it is either the choke coil is burnt out, or that my carb connections are getting hung up some how... what can I do to check that everything is moving smoothly? I figure I should wait till it devlopes the problem, take off the entire air cleaner housing, and just start checking things (throttle connections, choke canceling cam, etc.?) Anything else I should do? How about lubricating? What lube should I use? Thanks for suggestions.

The choke problem you are experiencing is very, very common. If you have a constant 12 volts at the wire to the choke with the engine running then replace the choke coil. If you have an intermittent 12 volts at the connection with the engine running then you have a grounding problem. There is nothing to be gained by looking further except the experience of doing so. Good luck!!!

Thanks for the diagnosis.. yes I am getting 12 constant volts at the wire.. I guess I'll just have to replace the coil as you said, thanks again.

Choke assembly

Well I went to NAPA today to try and order the choke coil... apparently they dont sell just the coil.. I have to buy the entire choke... in his words "the place where the electric choke wire goes into and the plastic piece with the coil inside" is the part that NAPA sells... from what I can tell thats the entire choke assembly... now, here is my dilemma, the price on the part is about $60 ... quite a bit for a broke college student such as myself.. I don't want to put this money up if I can't install it myself... since I no longer have to drill out the rivets, wont this all be easier?? Am I getting into something I don't know anything about? The idle situation is getting worse and worse... almost so that it is undriveable... its either I fix it now.. or save up to take it to the mechanic... what does everyone think? Also.. if you do think I can tackle this project... can you give me a short outline? Thanks a lot for any info and advice you can give me.

Both NAPA and Autozone call the part that you need a "choke thermostat". Basically it's a replacement coil(thermostat), new cover, 3 self tapping screws(to replace the rivets) and 3 curved retainers that the screws go through. NAPA price online $53, Autozone price online $32.99, so I guess I would go to Autozone and save a few bucks. You will still need to drill out the 3 rivet heads, remove the old coil & cover, then with a small drill bit drill out the remaining rivet shafts. Be sure to use a drill bit smaller than the replacement self tapping screws so that they can form their own thread. When you install the new coil make sure that it properly engages the tang that sticks through the back side of the housing. This is physically what engages the moving element and causes the choke butterfly to open as the coil(thermostat) heats up. The kit will come with an instruction sheet, and a diagram. You should be able to do this if you take your time and follow the directions. You will see graduation marks on the new cover, start at zero, see how your car starts/runs when cold, and determine if you want to go richer to as much as 2 or 3 marks to the rich side. This will keep the choke in for a longer period of time.
Thanks DDL-81! I ordered the part last night from autozone.. I really appreciate you looking up the prices for me too. What would I do without all of you?? Thanks again.

Well... big trouble today. I installed the new thermostat.. no problem there... but I could not get the fast idle to go off!!! No matter what setting I put it on, could not turn off the fast idle. It was reving up to 2500 rpm.. terrible.. I had to turn it off cause it was getting very warm too.. did not sound good.. Any suggestions anyone? I managed to put the old one back on and have it work like it did before.. so.. a small victory? I think im gonna return the new thermostat and get my $40 back... Time to call the mechanic. Thanks for all the help everyone, regardless of how it turned out, at least i learned a little bit more about my vette today.


I am not sure if you ever mentioned that you own a shop manual for the L81, but here is an abreviated procedure for adjusting the fast idle while the carb is on the engine.

On my Holley carburator it is suggested that this is done while the engine is off, for the fast idle screw is most visible while the throttle is wide open; however, on the Rochester Q-Jet carburator you should be able to see the screw as shown in the picture.

I suspect also that the engine timing was not disturbed. Let see...oh yeah...obtain the proper fast idle cam setting from your smog label under the hood. The label will tell you where to locate the fast idle cam while you adjust the fast idle speed.

The picture is showing you what the linkage looks like behind the choke housing. So you need to use a bit of imagination. Good luck! :upthumbs

Thank you for all the help, I really do appreciate you taking the time to walk me through it step by step. I do not have a shop manual (looking for a good one on e-bay) but I do have a haynes repair manual. I know exacty the location of the illustration that you provided. The problem was not only the high fast idle, but it would not disengage. It was reving at 2500+ rpm and not doing good. Once the choke was closed all the way shut (after trying to make numerous adjustments) and smothered the engine so it wouldnt even start up.. really scared me. I am really starting to question my mechanical inclination. Is it possible that the choke wire was not connected properly? It just didnt fit as snug on the new thermo, and I did not connect it back up when I reinstalled the old unit, but as soon as I did install it, the fast idle turned off.... Either way I think Ill give it one last try tomarrow.. as scary as it all was.. Thanks again though, I cant begin to tell you how much you have helped me, and the money saved.


P.S. I did not have to drill out any rivets, there were 3 screws with retainers already in the place. I suspect that the previous owner may have done the same thing? Good thing though because the new thermo did not come with any self-tapping screws.
I had a really similar problem with my car when I got it and couldn't figure it out. I finally took it to a mechanic and he found it in 5 minutes. The old owner had dropped some pieces of an old rotor in the distributor and it was screwing up the module. The RPMs would be all over the place. Once he got the stuff cleaned out it ran perfect until I shorted out the module but that's a whole other story.

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