Hey gurus, been working on my 84. Did a complete tune up, water pump, fixed some wires, and she runs fine with no misses. I shut her off and then restart her, runs fine, and then after about a minute or so, the idle starts to go down and then the check engine light comes on and then the idle comes back up. Tried this, the off and on about 4 times with the same results. I do say HER cause she is a picky bitch, no offense to anyone! Any ideas where I might be having a problem? TIA for any clues Mark

Well... you need to read the code, first.

On the ALDL (above right knee, drivers side), using a paper clip (real hi-tech, eh?), jump pins A and B. This will enable the ECM to tell you what the code is. A and B are next to each other. Top right, and next left on the ALDL.

If you look at the front of the ALDL:

-------------------------
| F | E | D | C | B | A |
-------------------------
| G | H | J | K | L | M |
-------------------------

* NOTE: GM does not use 'I' or 'O' on their connectors, look too much like a lower case 'L' or a zero or one.

Turn on the key - DO NOT START THE ENGINE! and start counting flashes. It is crude, but that is what it is.

Code 12, IIRC will present first and last. Code 12 confirms that the computer is communicating and Code 12 at the end indicates thats it for codes. It will present as:

<flash> short pause <flash><flash> longer pause
[repeats 5 times]
LONG pause

A code, lets say 33, would present as:

<flash><flash><flash> short pause <flash><flash><flash> longer pause [repeats 3 times]
LONG pause

Any additional codes would present next, say, code 24:
<flash><flash> short pause <flash><flash><flash><flash> longer pause [repeats 3 times]
LONG pause

You need to get the code before we can assess the problem.

If you don't get any flashes, then I made a mistake. Or you did. Or the engine controller is screwed.

Ok, gang, what am I missing here??? It's been a while!

Quote:

Looks fine to me
Shorthand version below

http://www.corvettebuyers.com/c4vettes/codes.htm

Thanks Guys, I will do the check tomorrow when I get home from work. Now not a good time, (beers). Nice that I don't have to buy a fricking computer to see whats wrong. THANKS AGAIN!!! and will let ya know tomorrow Mark

Oz - excellent, my memory isn't totally shit.

Mark - Looking forward to what you learn!!

Worked exactly like you guys said! I came up with code 44. Dont know what that means, or where to look for that. Help? Mark

Bad O2 Sensor.

It's showing lean.

Whatever you do, don't get a Bosch one... Get NGK/NTK or Delco. Denso are good, too.

cool thanks, how many does this car have? I have a 99 Expedition and it has 3 of em. Took it in when the ck engine lite came on, and the fricking shiesters wanted to change all 3 of em. I said hell no and checked things out myself and found 2 bigtime vacumn leaks. Did the battery dealio, and the lite never came back on. A little more info on this car: I did a tune up, like I said earlier. 2 spark plug wires were shot, and about 3 or 4 plugs smelled of gas pretty good. The buddy I got it from just told me that he had to change the intake gaskets, and screwed up on the throttle linkages. So I guess it was sucking fuel bigtime. I know that after the tune up and all I am not smelling the gas fumes like I was before, when I am starting it up in the garage. And NO I am not a dumbass starting it with the door closed LOL So 1. how many? 2. should I try to reset the computer? 3. just buy what I am going to need? Sorry so long winded, I am learning. Thanks Mark

Should have just one O2 sensor on the drivers side. If you don't have a FSM get one. You can try to reset the computer and see if it returns. I'm sure some one else will chime in.

Ok trying to reset the puter didnt work. Whereabouts do I go looking for the sensor on the drivers side? Also what is a FSM? Mark

FSM = Factory service manual. The O2 sensor is on the y pipe near the back of the motor on the drivers side I believe.

it's the only O2 back there. Near where the Y pipe merges.

You can't miss it... it will have a wire coming out of it!

Code 44 doesn't necessarily mean bad O2 sensor, it means it's detecting a lean condition.

Could be one of several things.

Here's the diagnostic pages from the FSM.

Attach file:

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1984 FSM code 44.pdf Size: 326.54 KB; Hits: 120

Thanks alot guys! OZ, that link you put up was cool, had all the codes, and what could be wrong, and where the sensor was. Also told about how not to assume that it is the sensor might be something else, like CC said. Got home and was looking for the sensor, (found it lol) and it looked like new. WTF! I looked thru the paperwork my buddy gave me with the car, and the 02 sensor was replaced in May of this year, the workorder stating the car was running rich. I dont know what brand sensor was put in, so Andy why is the Bosch brand no bueno? And could his be the prob?, or is CC on the right track, that it is something else. I am wondering about the fuel pump, I see there is a block off plate, on the block. So I am assuming it has electric? Thanks again guys, sorry for all the questions, but I am learning the chebbie stuff!!!

Yes, the 84+ Corvette is injected, so the pump is in the tank.

I had a ton of problems with Bosch O2 sensors... they just didn't last. I was replacing them every 3 months until I got disgusted and switched to NGK. I hate to say it, but the Bosch units are made in Mexico... and I think they are having QC problems. They won't be the first company to have issues with QC with products made down there.

NGK O2s are made in Japan. If it was made in Mexico, it is possibly a Bosch...

Also, you have issue with the tune and the car running very rich at times. I wonder if the O2 was beat up by that situation.

I was thinking the same thing, about the tune, and how it was running before that. I am going to replace the sensor regardless seeing that they are pretty cheap.

Just don't get a Bosch!!!

You got it my friend, picked up one today from the Napa by my house for 24 bucks and its an AC Delco!!!! Told them I did NOT want a Bosch. Like I said also I was going to change it no matter what. Going to do that tommorrow and see what happens.

I is one helluva happy camper. Put the new 02 sensor in and she be running good, and no check engine light. Mustve been the bad running engine, like ya said Andy,, that tweaked the sensor. YEEEEHAAAAAAAA

yay!

I am a firm believer in diagnostics... but when a car has had a number of other issues, I look at the downstream cause/effect, and in this case, your issues easily added up to a bad O2 sensor. Considering they are not expensive and are normal maintenance items, it made good sense to replace it.

Now, drive that car!!!

Glad to hear it's fixed.