My 85 is giving me another problem. This time, I'm getting a code 34.

Symptoms are, hard to start when cold occasionally, and very rarely will start but not accelerate at all (this is the only time cel comes on). If I turn it off, let it set about 10 seconds, then crank it, everything is normal again.

My idle is alittle lower than I'd like, its between 700 and 800 rpms, rather it be around 900. When I stop at a light, it holds idle, but jumps and jerks alittle, not bad, but noticeable. Runs great as soon as I hit the accelerater, all the way to the redline.

I figure either the maf power relay is bad, or the burn off relay. If I disconnect the maf, the car runs like poo, it idles good, but you cant go anywhere.

So whats the problem you say? buy the relays and change em right. I don't have a service manual, but know there is supposed to be two relays on the firewall behind the battery, but I only have one! I found two other relays like this about the engine compartment, one is by the drivers side front tire, the other is close to the distributor on the firewall. Has one of mine been moved?

I have an empty connector in the area, but it is 5 prongs and I believe it was supposed to connect to the cruise control module, which I don't have anymore.

sorry for the novel there, but I'm lost. Maybe a couple of pictures highlighting the relays could get me going in the right direction?

 

The 85 came with a MAF module which was replaced in 86 with the 2 relays. Hard to find(purchase) and hard to get at(replace). Search using 85 MAF, you should find more info. I can't offer much more because I have an 86.

 

yep, thats my luck. i'll search and see what I can dig up.

 

I am new to this but I have book that I can look in for you. Your MAF, is it a Bosch or Delco? Different diagram for the two.

 

Mine is a bosch, thanks for the help.

 

Bosch.

1. Clear the codes and run engine until the check engine light comes back on or you are satisfied that it will not. Does the code 34 reset?

If NO, the condition no longer exists. No repair is indicated at this time.

If YES, disconnect the Mass Air Flow Sensor and run the engine 2 to 3 minutes. Does code 33 set?

If NO, the mass air flow sensor signal wire is shorted to ground for the ECM is faulty.

If YES, Check for 12 volts available to the mass air flow sensor. If the mass air sensor is receiving 12 volts check the mass air flow sensor ground. If the ground is okay replace the mass air flow sensor.


I typed it word for word from the book. The part about "for the ECM is faulty" is odd wording but that is how they worded it. I hope thats not an issue and you fix it before then.

Good luck!

 

Thank you for that, what I did earlier was pretty similar, but not the same. I cleared codes, ran it at 2000 rpm for a minute, then checked the codes, no codes. So I ran it for a couple days, checked the codes, and there it is. I find the problem to be very intermittent, usually just in the mornings when its been sitting for a while. I do know that other things can set a 34, like a bad air filter, or improper idle setting, so i guess I'll look at those possibilities next.

Nothing should be bad on this car, everything was redone a year and half ago, makes me think airfilter or something along those lines.

 

Code 34 is Mass Air flow sensor Low. This can sent for several different Mechanical or Wiring reasons, which the service manual diagnostics will find - or it can set if:

When you start the car up it "flashes" to life, with as much airflow as the IAC park position and the throttle blade shut position allow, then settles down to the IAC position commanded by the ECM (based on RPM's, temp, etc.). Where the IAC is coming from - where the IAC Park position was, also set in the PROM program - makes a difference, as does the position of the throttle blades in the TB - the "Base" idle adjustment.

If the IAC park position is not reasonably close to where the IAC position is going to be commanded as it settles into idle, or if the Base idle position of the throttle blades is not right, in this case too far closed, then there will be a second or so where the airflow is too low - and the MAF will see this - and the code will set. After That you are done, the ECM is in "limp-in" mode, it isn't going to run well at all. The Check Engine light will be on..

Also - vacuum leaks will drive you nuts with this. Any air getting in that the MAF doesn't see, particularly when the idle AF is so low anyhow, will make a code 34 Very easy to set at startup...

This may not happen every time you start the car, or may be more likely to happen Cold, and less likely with the engine Warm - depends on what is not set right, how far from the correct setting it is, which Side of the correct setting is it on, etc.

Usually if the code sets you can shut it back off, then start it right back up and it'll be fine (shutting it off will reset the limp in thing). Usually, if you Expect it to set the code, you can tickle the throttle open just a bit with the pedal as you crank it up - holding the ECM just off idle (it's looking at the TPS setting here..), and not letting the air flow get low enough to be a problem. Not until the rpm's have settled down and the IAC has caught up to nearer where it should be.

The Right answer is to re-set the Base idle (and then the TPS) per the service manual. Then, if it still insists on being a problem, change the IAC park position values in the PROM program to hold it a bit more open - that'll fix it.

BTW - if you have things set too Open - too open an IAC park position or too High a base idle throttle blade opening, then you can go the Other way and have too much airflow when it flashes to life - setting a code 33 (I think). Really the same problem, just in a different direction...

 

Thanks for the help ron. I personally didn't think it was the control module going bad causing this, but I could see it needs its idle raised just a hair. I'll do the base idle setting and the tps adjustment and see where that gets me.

 

Idle speed is burned into prom. Code 34 is what it is, a code for MAF readings outside parameters that the ECM is looking for. I don't think messing with min idle is going to cure your code, but it may help with other problems.

 

True - But...

An incorrect base idle setting (too far closed on the throttle blades) or an IAC Park position (per the PROM) that is too far away (closed) from where the IAC will need to be to maintain the desired (per the PROM) target rpm's - either one or both of these will/can cause a low air flow condition Immediatly after the motor fires and the timing control switches to the ECM (from the ignition module).

If the code 34 sets Immediatly on the motor firing up it's very likely that the problem is in one or both of those settings. Assuming, of course, that all of the "usual" wiring and "mechanical" possibilities in the MAF circuit check OK.

Been there, done that.