CEL at low idle
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: Mulvane KS
If the check engine light comes on at idle, then goes off after moving(changing acellerator), it is most likely the TPS (throttle postion sensor). this is located on the front left (driver's) side of the carb, and has a plunger that travels when the linkage is moved. You need to jump pins D to E (on connector under ashtray), turn key to on (dont start), then watch the codes from the flashes on the CEL. It will go thru 3 code 12s, flash, flash-flash. Then it will bring up the active codes 3 times each. then it will go back to code 12. code 21 is the TPS circuit. A lot of times, the signal at idle to the computer is low. The computer can be fooled by increasing the idle speed. this will increase the voltage signal back to the computer (provided the TPS is not completly bad). If you dissconnect the battery for more than a few seconds, all the stored codes are erased, so check before disconnect.
Thread Starter
Melting Slicks
Joined: May 2003
Posts: 2,078
Likes: 282
From: Dyersburg TN
and so...
Oil pressure is good thanks.
so that's where the plug is. Oh well I learned the dash underside well looking for it
I have a autoxray 5000 I will try on it. This is my first C3 and I had decided the computer did not have a port.
thanks for the info
so that's where the plug is. Oh well I learned the dash underside well looking for it
I have a autoxray 5000 I will try on it. This is my first C3 and I had decided the computer did not have a port.
thanks for the info
Burning Brakes
Joined: Dec 2007
Posts: 952
Likes: 0
I doubt it will work. 81 is very crude ECM.
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Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: Mulvane KS
code 21 is TPS throttle position sensor. You can check with a digital volt meter. With engine running backprobe the connector on the carb at the center (B) and vottom (C) wires. Hard to tell colors after wires age, but the center one is dark blue and the bottom one is black. The other wire (C), grey, is +5 volts from the computer. The voltage at idle should be ~.56 volts. Check with AC off.
Code 34 is vacuum sensor circuit low. The vacuum sensor is attached to the firewall on the drivers side. It will have a vacuum line from it directly to the intake manifold. Its about 3 inches long X 1 1/2 inches wide. Its hard to see because it sits under the mounting bracket. Sometimes these are called manifold absolute pressure sensor. You can get one at most auto parts stores. Not a lot to go wrong with them. I would check the vacuum line going to it. It it came off, the engine would idle higher, and could cause both codes to come in. The best purchase I ever made was a Chevrolet shop manual for my 81. They come in real handy when it comes to the CCC system. All the codes are explained and also has step by step troubleshooting . This way, you dont have to replace sensors that arent bad. Sometimes one bad sensor can cause two or more codes to come in. Hope you find the problem
Code 34 is vacuum sensor circuit low. The vacuum sensor is attached to the firewall on the drivers side. It will have a vacuum line from it directly to the intake manifold. Its about 3 inches long X 1 1/2 inches wide. Its hard to see because it sits under the mounting bracket. Sometimes these are called manifold absolute pressure sensor. You can get one at most auto parts stores. Not a lot to go wrong with them. I would check the vacuum line going to it. It it came off, the engine would idle higher, and could cause both codes to come in. The best purchase I ever made was a Chevrolet shop manual for my 81. They come in real handy when it comes to the CCC system. All the codes are explained and also has step by step troubleshooting . This way, you dont have to replace sensors that arent bad. Sometimes one bad sensor can cause two or more codes to come in. Hope you find the problem
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: Mulvane KS
Also, if you find and fix the problem, even though the check engine light will be off, the previous codes are still in the computer. Usually when I get a code, I write it down. After working on the problem, I will disconnect the battery for a few seconds to clear the codes. That way, if a new code comes in, when retreiving it, you wont have to scroll thru all the old codes to find the new one. These computers are very primative, but they work well.