Rough Idle
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Joined: Mar 2006
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From: Auburn New Hampshire
Rough Idle
I recently purchased an 89 Corvette (115K miles) with a rough idle. The idle appears to smooth out as your driving with higher rpm. The previous owner reported the trouble started subsequent to his mechanic installing new plugs, wires, cap and rotor as well as new exhaust. I pulled the plugs and they are correct, ignition coil values were off and I replaced but the problem still exist. After replacing the ignition coil and running the engine for a few minutes the check engine light came on. Can someone tell me how to retrieve the trouble codes. Now that there's a check engine I'm hoping the codes may point me in the right direction.
Thanks...
Thanks...
Le Mans Master
Joined: Oct 2003
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From: seattle WA
Nope, someone will post a site for you. But it's pretty easy.Above your knee while in the drivers seat there's a little box..this is the ALDL, remove the cover if it's still there, you'll see a row of pins, top row has six I think, bottom just 1. You're interested only in the top 2 pins on the right hand side, refered to as pins A and B. With the ignition OFF short (or jump) pins A and B, turn the ignition switch to ON, BUT DO NOT START. in a few second the Check engine light will begin to flash a code 12, flash pause flash, flash. This should happen 3 times, after this happens 3 times you will you will get an error code (or codes), or you will get another string of code 12 if there are no error codes. A string of codes would read something like this..just an example: 12, 12, 12, 36, 36, 36, 44, 44, 44, 12, 12, 12. You may just have 1 code or several like I just described.
Once you get the codes...post and maybe we can help.
One thing you definetly want to get is the FSMs..that's Factory Service Manuals, best investment you can make, about $100 for both volumns.
Once you get the codes...post and maybe we can help.
One thing you definetly want to get is the FSMs..that's Factory Service Manuals, best investment you can make, about $100 for both volumns.
Last edited by rick lambert; Apr 26, 2007 at 12:35 PM.
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Joined: Mar 2006
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From: Auburn New Hampshire
found nothing there. but found this link from a previous post.
http://corvettebuyers.com/c4vettes/ecm.htm
thanks
http://corvettebuyers.com/c4vettes/ecm.htm
thanks
Le Mans Master
Joined: Feb 2006
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From: Louisiana
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Doubt the trouble code has anything to do with it, but of course you need to fix that problem. The usual reason for a rough idle is because one cylinder is making less power than all the others. You can isolate it by cutting some 1/4 inch vacuum hose into 1 inch pieces and inserting a piece between each plug wire and the distributor. Then kill each cylinder by touching each piece with a grounded test light while observing a Tach. The cylinder that's the problem will not drop as much as the others. Once found, and with all that you've replaced, suspect an injector. OR, and since this is an '89, if it's #7 or #8, suspect the head gasket. Remove the plug and examine the threads for rust or an electrode that looks different than all the rest. Check compression; perform a leakdown test.
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Joined: Mar 2006
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From: Auburn New Hampshire
Well, I ended up pulling a 32 ECM error code which I'm told is pointing to a potential EGR problem. I'm picking up the EGR (temp/diag) switch at the local dealer tomorrow and going to replace. Let you know how it goes.
Thanks all for suggestions
Thanks all for suggestions
Racer
Joined: Oct 2006
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You sure you have a stock camshaft? What kind of roughness is it? Is it misfiring. Are the rpms going up and down. Does it stall when you first put it into gear? Is it jerking hard (ignition problem). Is there a knockingt or rattling noise associated with rough idle (loose/broken mounts).
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
32 means EGR was commanded and the heat sensor, which should close when exhaust flows by it, remained open. In other words, the voltage signal at the ECM didn't drop to zero, so as far it knows, the EGR event didn't take place and the Check Engine Light pops on and the code is stored in memory. EGR is only commanded at cruise, so it will illuminate the Check Engine Light when the event occurs - and then turn it off after it's over (like when you come to a stop). Clear the code and then go for a ride on the Freeway and see if it comes back. If it does, check the vacuum harness. It runs from under the throttle body to a tee where one side branches off to the EGR solenoid - mounted on the thermostat housing - and the other side runs to the Charcoal Canister in the left headlight well. Mine likes to fall apart at the T - your findings may vary.
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Be sure and check the EGR valve diaphragm, too. Mine had dry-rotted after years of intense engine heat and failed to hold vacuum when I hooked a Mity-Vac to it to confirm operation.
I replaced the EGR valve with a new one, cleared the codes and voila! No more Code 32.
I replaced the EGR valve with a new one, cleared the codes and voila! No more Code 32.
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From: Auburn New Hampshire
Thanks all for all the great suggestions. Well, I ended up finding two cracked vacuum lines in the egr vacuum harness. I wanted to replace the whole harness given the age of the vette and to prevent chances of future type occurences. My local GM dealer informs me the vacuum harness is a discontinued part and they were unable to locate from their online parts at other dealers. Any suggestions where to purchase a harness or components to build.
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