First Fire & MAL #34

[~JM~]

First fire on newish top end. A couple of problems I need to resolve pasted below.

Problem #1: I replaced the driver side header with one from TA Performance. The OEM crossover pipe does not mate up well between the two headers now. I think the outlet flange on the TA header is larger diameter & taller. I have an exhaust leak on the D-side that I'm assuming is coming from there. Suppose I must now order the TA crossover to make it work. Sure wish these companies would either QC or communicate better. I'm trying to remain grateful that parts are even available.

Problem #2: When I bring RPM up to about 2K & release the throttle, the engine almost returns to idle, but then sputters & dies. Re-starts just fine. On initial start the Scanmaster displayed MAL #34 MAF Low Signal, but it cleared upon re-start & has not reappeared. I have a 3.5" LS1 MAF (plastic housing by Standard) & a MAF Translator. This is new equipment for me. The dip switches are On-On-On-Off. I have not attempted any adjustments yet.

Today was initial start, run a minute or two & shut-down, check levels & look for leaks. Engine started on first attempt, no drama. Re-start & increase run time, vary RPM & heat cycle several times.

[Steve Wood]

Maf Base set to 0?

Here is the troubleshootin g for 34   https://vortexbuicks-etc.com/code_34.htm

[~JM~]

Maf Base set to 0?

Here is the troubleshootin g for 34   https://vortexbuicks-etc.com/code_34.htm

Yes MAF Base @ 0

I do not have the proper air cleaner yet. Hopefully it will arrive in the next day or two. Not sure if that will make any difference.

[Steve Wood]

Be sure the iac passages are clean in the throttle body and the iac is working as it should.

Check your O2s to be sure they are normal at idle.  Watch what they do when you let off the throttle.


Check all the hose joints between the MAF and the throttlebody to be sure they are all tight.  See if the idle vacuum is what it should be.  Be sure the plenum is snug and all the other usual things.  

[~JM~]

Be sure the iac passages are clean in the throttle body and the iac is working as it should.

Check your O2s to be sure they are normal at idle.  Watch what they do when you let off the throttle.


Check all the hose joints between the MAF and the throttlebody to be sure they are all tight.  See if the idle vacuum is what it should be.  Be sure the plenum is snug and all the other usual things. 

Throttle body is fresh 62mm rebuild from Steve Monroe. I adjusted IAC set screw & TPS some today. Idle increased to 900+ RPM & IAC numbers increased. Went the other way & IAC numbers are 0-4, idle is 825-850. TPS is .40 with engine off & .42 at idle.

O2 is in the 750-800ish range. Did not observe during throttle chop.

First start on top end rebuild. New hoses, vacuum lines, check valves, new MAF & translator, fresh gaskets, everything is tight. Do not have a vacuum gauge installed, but I have a temp one I could use.

Beginning to think it might be turbo back surge. Is that possible? I just replaced OEM turbo with Precision 5858. Have 3" inlet pipe with 3.5" LS1 MAF. Still awaiting the air cleaner. Should arrive this week. No drive time on ECU/chip. Just garage run time.

I disconnected the orange wire this morning for a few minutes, then connected & started engine. MAL #34 has not returned. No other MAL codes either.

[Steve Wood]

Okay, first.  If there is no air filter in front of the maf, that may well be your problem.  The air flow may not be smooth enuf for the maf to meter properly.  This is speculation on my part, but I have seen strange things when the air flow is not right.

With regard to the turbo, it should not have any effect on how it idles or transitions if there is no boost.

The tps settings do not matter whether they are .36 or .46 as long as they are within that window.  The computer sets the idle speed and controls it.  If you screw in on the iac, it may increase the idle speed, but, when you shut the engine off and then restart it, the idle will go back to wherever the ecm commands.

If you screw the iac screw inward, the tps voltage will rise but as I said above, the idle will go back to what the ecm commands when you reset it.  If you screw the iac screw in far enuf, the Iac numbers will approach zero and as they get there, the iac no longer works as an iac and the screw becomes an idle adjustment screw and the computer will lose control of the situation.  Altho we all talk about magic Iac numbers, I really have seen virtually no difference between iac readings of 20 and iac readings of 40 with modern chips.  The iac keeps doing its job.

Of course, we are talking about iac numbers that are taken in Park on a warmed up engine.  When in drive, the numbers should go up quite a bit as the iac is more active trying to maintain a constant idle speed as it has to adapt to the load on the engine which causes the idle speed to want to vary more.

I generally try to set mine in Park/warmed up to be around 30 but as I said, it really does not seem to be sensitive to a given number.  As long as it goes up in Drive, it would seem to be working.  Obviously it is idle air control and has zero effect once you mash on the gas pedal a little.