Code 34: (1985-1990) Clean the throttle body. Check MAF connections. Replace MAF relay. Replace MAF Sensor. Possible ECM failure.

This AM I let the car idle and warm up for about 5 minutes while I walked my daughter to the bus stop. Seemed to be idling just fine. I was curious if the code 32 had disappeared yet since I replaced the EGT switch a week + ago. I shut the car off - did the paperclip in A&B & checked the codes. Still had code 32 showing. :( I took out the keys & the clip and tried to restart the car (now warmed up). I would barely start. Once I got it started (using the gas pedal ala my '70 w/ carburetor) it wouldn't idle - it would just stall. I was able to finally get it going and put it in gear and back into the garage. The SES light had come on. I checked the codes again. Now it had 32 + 34. It seemed to start OK after that and drove around the block OK. I thought I'd take it to run a quick errand. It started out OK, but 15 minutes into driving (40mph, traffic lights etc) wasn't running well - idle was erratic between 4 - 700 RPMs. It stalled a few more times. Idle would just keep dropping down and the computer wouldn't 'catch' it before it stalled. I limped it back home
and drove the '70 to work. (Three vettes - it's a wonder one is running at any given time!) :lol:

If you recall a few weeks ago it was pinging horribly under light load. I added injector cleaner to 2 tanks of gas in a row and put in the 94 Octane stuff - that cleared it up so I wrote it off as bad gas (or misblended 92 octane at the local station - they don't have 4 tanks but blend the various grades as it's pumped.)

What is the likely culprit? Could it be related to the code 32? Just how difficult is it to 'clean the throttle body'? All my '87 manuals are at home. :eek: I'm pretty handy and my husband is great with this stuff (though I'd rather do this myself to learn - the reason I bought the 87 in the first place). I guess I'm just wondering what the possible scenarios are for fixing this and how fail proof is following the Service Manual? From what I've read in there before it seems to be pretty explicit as to cookbook directions.

Should I first try disconnecting the battery to reset all the computer stuff and see if the same problem comes back up? That Microsoft joke where the solution is to get out of the car, reboot and try again comes to mind. :lol:

Thanks for any input. BTW< I checked the archives and recent threads etc in C4 and C4 Tech for 34 and nothing!! came up. :confused:

 

I am beginning to believe that Bill Gates wrote the software for the Vette's ECM...

You are on the right track... as for the idle, check the IAC. Thats what everyone says at least! :) also check the TPS.

The 32 is still in the computer... you can pull the battery and wait 20 minutes for it to clear and see what happens.

If it comes back, you have a problem.

 

Did you replace BOTH MAF relay's?

Did you pull the EGR off and make sure it wasn't stuck open?

 

Thanks for the feedback. :) I replaced (due to the code 32 problem of a few weeks ago) the EGT switch. This gizmo - (Only saw one) http://www.corvetteforum.net/c3/juliet/egtswitch2.jpg

No. I haven't found the MAF relays even yet. ;) Haven't pulled the EGR off either. I'll see (between handing out treats) if I can do that tonight. Consider me blonde and clueless, but willing to become a gear head. (Not too far from the truth actually... :lol: ) I'm at a disadvantage here - what is the EGR? Is that those grooved aluminum things which run alongside the intake runners? Or is that the part in front? :crazy: You can tell I haven't spent hours under the hood of a computer controlled car comparing parts with the labels in the diagram. (Just so you know that I'm not totally mechanically inept - I can rebuild quadrajets - a lot of good it does me here though.) :jester I think I just need some really basic help walking me through this if you all can put up with a long string of dumb questions. :bb :bb I'll be online tonight for sure.
Thanks, ~Juliet

 

Must say I had the very same thing happen to my 87 when I got it. The final fix was replace both relays (behind battery) and replaced the IAC. Now works great. Seems I had two problems. It is possible you have a bad MAF though, even new ones can be bad but would try the relays and IAC control first. Don't get the IAC from the dealer, they want WAY TOO MUCH. Got mine at bumper-to-bumber for $25. Good luck.

 

Is there a way to bench test these relays / sensors? What about the IAC?

 

It's a pain to test the relays, Don't think it would be reliable to do so because the relay might test good with a meter but fail in the car. I got mine from the dealer for $12, being that old wouldn't hurt to just replace them. They were a pain to get to for me (big hands), didn't want to remove the battery.
My car would idle sometimes but mostly I had to hold the brake and push the gas a little at stop signs (not fun). The tech section has a pretty good write up on how to replace the IAC. When your done there should be a little red wire off of the battery, just unplug the connector for about 30 sec. to reset the computer and see how it goes. It was really bugging me, doesn't look good to be in a shiney vette that dies at the stop sign for everybody to see. :crazy:

 

The EGR is the round valve smack dab in the middle of the intake manifold, (Under the plenum). Pull the plenum off. When out, the valve should be closed (no air gets through). If not, it is bad.

The MAF problem is most likely the relays. Replace them both. They are both the same P#. They are low$. If that doesn't help we can go from there.

 

I got my relays at Autozone for about $9 each. they are cheap enough to buy and difficult enough to test, that I would just get new ones, even if this doesn't totally fix your problem you probably need new ones anyways. As to how to replace them....

They are behind the battery on the firewall. You need to re-use the metal bracket that the old relays are on. Just unplug the relays (remembering which plug goes to which relay, label if necessary), unscrew the bracket from the firewall, remove the two old relays from the bracket, put the new relays on the bracket, plug relays in, screw bracket to firewall. Done. Notice that there is a slight difference in reassembly order. It is much easier to lug them back in before you screw them to the wall. this cleared up my code 32. I have, on several occasions :bb , forgotten to re-attach the MAF plug to the MAF and boy does that mess with my idle. After you replace the relays, disconnect the battery for about 10 seconds to clear the codes, then start the car and see what happens. If you still have a very rough idle check your codes, as your MAF, or the wiring to/from the MAF may be bad. check the connection, the plug is on the bottom of the MAF.


Bob


[Modified by BobMachus, 10:48 AM 10/31/2001]

 

I could actually tell if the SES light was going to come on the next time the car got started by listening to the relays when you turn the car off. You should hear two clicks about 2 seconds after the car is turned off, that's the two relays behind the battery going through the MAF burn-off sequence. If I only heard one click the light would come on next time. I think the car has to be running and warmed up because if you start the car right away after shutting it off it won't do it. Maybe not too usefull but it's interesting to know how the car works, learned this from my 88 GTA

 

Disconnect the battery for 10-20 minutes, and replace the relays. They are located behind the battery. They are fairly inexpensive and easy to replace. Most of the time the relays are the culprit.

 

I dug out the service manual. It doesn't make any mention of the relays in reference to code 34. It describes a procedure to test the MAF sensor - disconnect, restart, look for code 33. I'm still learning to understand these manuals & diagrams. The manual mentions if code 33 does not set the CKT998 is shorted to ground. But that circuit doesn't seem to go to the relays - just to the sensor. Also how do I find the diagram and part number in the parts manual from the service manual? I couldn't seem to find any cross reference numbers. Maybe I'm missing something here. I'm going to go see how to 'disconnect the MAF sensor' now. BRB, ~Juliet

 

Found the relays and the part in the parts manual. GM part #14089936. List price (on my ancient book) of $6.60. So probably double that now. :yesnod: I'll order them tomorrow. BTW, are they inside those cute little boxes with the silkscreened circuit diagram on the top? Or is that the entire unit itself? I'm wondering if the ones in my car are original or not. (Sorry, my NCRS purist side is sneaking out. :D )

I'm going to disconnect the battery to reset the codes, then start it up and see what happens. If I get code 34 again I'll try disconnecting the MAF as described in the serv manual and see what happens since I don't have the relays now anyway.

 

BTW forgot to mention - DEFINATELY useful to know. :seeya Thanks. ~Juliet

 

I think I'm getting the hang of this computer thing here. :lol: According to the manual it's a bad MAF Sensor. Is it possible that bad MAF relays are resulting in a false MAF reading? Is there a something with a procedure for diagnosing bad relays? (I'm going manual digging now... )

OK - I'd saved some stuff to disk a while back on how to clean the throttle body. One of the online diagnostic sites mentioned that as a possible cause of code 34. (Code 32 is now gone BTW). I'll try cleaning the TB tomorrow before I order some $150+ MAF relay. :eek: If nothing else it ought to help the idle. I'm going to try the completely removing the TB to clean it approach. Do I need to buy any new gaskets or anything before I can reinstall it? What's the difference between TB cleaner and Carb cleaner? I've got plenty of the latter floating around - guess I can swing by PepBoys and get TB cleaner if need be.

Would ancient (as in original factory) spark plug wires & coil & injectors cause any of these symptoms on a 107k mile car?

BTW, when I tried to start it (w/ & w/o MAF connected) the car wouldn't hardly even start without a whole lot of coaxing of the throttle and then it really STINKS! Gas - exhaust - the nasties, even worse than my '70 (no emissions) exhaust when it's running rich! I'm not sure I even could limp it to the dealer (5 miles away) if I had to... so it looks like I'm in for fixing this one myself. :boxing

Thanks for all your help & putting up with all my Qs. :flag ~Juliet


[Modified by Juliet, 12:06 AM 11/1/2001]

 

You'd be lucky to even get the car to run by disconnecting the MAF.
Judging from what you've done so far I would still lean toward it being the relays. Not sure what you where looking at but the relay looks pretty much like the one thats on the drivers side wheel well. This is where they are...
[img]http:/www.rayisd.com/maf.jpg[/img] .

When you say you disconnected the battery I assume you mean that you unpluged the little connector (little red wire off of the battery, should be with the main red wire), its a pain having to disconnect the main wire just to clear the computer while troubleshooting. 30 seconds should be plenty of time.
Guess it could be the MAF but like I said mine did the same thing, it had a code 33 & 34. One thing you'll learn with GM ecm's is that when it says code 34, replace MAF it can very well be the circuits that feed the MAF (in this case the 2 relays). Good luck, post any more questions that you have, they'll get answered.

 

I don't see the picture that I included, try it again.

 

I completely disconnected the ground wire on the battery - the main black wire. That seemed to work OK.

Thanks for the pictures. That's the area I was looking for the relays. There are 2 black box things with white screen printed circuit pictures on the top. These are the upper 2 most things on the aft side of that little area. Down lower towards the bottom there is another connector thing - I can't tell if that's just a connector deal or if there's another electrical component in there. Then I saw another gizmo on the inboard side of the battery closer to the engine and further forward. If I don't end up working real late, I'll be able to pick up the relays and install them and see what happens. Lets hope that it's the relays because the MAF sensor is $529.93! :eek:

Glad I've got you guys here to help me with this because just reading the service manual it clearly states that if you get code 33 with MAF disconnected and code 34 with it connected that it's a faulty MAF sensor. They refer you to the diagram (which does show the relays in the upstream circuit to the MAF relay) ONLY if it's an intermittent problem and you don't get code 33!

At any rate between the 2 relays and a TB cleaning I'll cross my fingers that it fixes the problem. Two questions on TB cleaning - I'm going to completely remove it from the car to clean it up.

1. Do I need gaskets etc before I can put the TB back on or are they all reusable (assuming one doesn't tear etc).

2. Can Carb cleaner be used on the TB or do I need to get TB cleaner?

Thanks. :cheers: ~Juliet

 

They are the cute little boxes with the circuit diagram silkscreened on them. Yes if the realys are bad it could make your car think the MAf is bad.


Bob

 

Yes, those are the relays. You can get a MAF from bumper-bumper or some other auto place for about $150 if you need to. That's another overpriced dealer item. I would also still lean toward the IAC for your idle problem. They are also about $25 from a auto parts store and are very easy to replace. Granted your throttle body might need some cleaning but my bet is the IAC.
:flag