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Discussion Starter · #1 ·
Anyone have any info on troubleshooting the mass- airflow sensor on a '93 4.2?
The diagnostic code on my RR is sporting the code "12" which indicates trouble with the MAF. I'd rather not replace it unless absolutly neccessary since its a $700 list part.

Trouble is the RR runs well, then develops a stutter occasionaly @ idle and runs rough(sometimes dies). O2 sensors are new, air filter is clean, idle bypass valve is new, cap/ rotor/wires are recent.
Any ideas would be helpfull.

Modifried-:confused:
 

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E-bay...you can find 'em for less than $100. I've got a spare one, but I've also got a strict rule about helping newbies...or anybody else, for that matter.
 

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Ryan,

Check your stepper motor too. It is known to cause similar problems.

Polla's LWB has the EXACT same symptoms you describe and we've done everything except mess with the MAF and stepper motor. We do not show a 12 code. O2 sensors are new too.

Oh yeah, and welcome!

:flipoff2:
 

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Serious One said:
Check your stepper motor too. It is known to cause similar problems.
tsk tsk...

...he said it was new :flipoff2:

FWIW, if you used the domestic equivalent you can pick up at Napa, I've heard they often do not function as well as the OEM unit.
 

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"replaced idle bypass valve" - AFIK this is the same thing as what most of you refer to as the stepper motor.

an often overlooked part: the emissions hoses - they must be pliable, and the t-fitting the connects them must be unobstructed.

start with the filter (or flame trap) that's installed on the forward end of the passenger side valve cover. trace the hose over to your right to where it connects to the t-fitting, and find a small hose that connects to the left interior of the intake plenum, and then a slightly larger diameter hose that connects just before the intakes butterfly . all three of those hoses tend to get hard and lose their seal, and get clogged up with gunk from the the dirty filter upstream on the valve cover. DAP sells a kit to replace the whole deal for about $65,


p/n: PK062 for '87-93
p/n: PK063 for '94-95

www.dap-inc.com

as an alternative, you can do like I did and clean just them all out really well with a good solvent , and use hose-clamps to make sure the fittings are tight.

as for the filter they are pretty cheap to replace, about $12, IIRC. But they are also very easy to clean :) There's a wire-mesh screen inside that can be carefully extracted and unfurled. use a bit of gas or brake cleaner to clean it up, doing the same to the cylinder. now is a good time to paint the filter body if you want. assuming you didn't knacker the screen, roll it back up and stuff it back into the cylinder, and it's good as new.

the plastic t-fitting will likely be clogged with very hard sediment - just use a small diameter drill bit to push through it. the brass insert can be removed, and both pieces can then be cleaned using the solvent of your choice.


there is another small foam vent on the other valve-cover that probably needs to be replaced, but likely doesn't have any direct bearing on your idling issue. it too is a cheap part, and probably worth taking care of while you're in there.

as for the MAF sensor i would double check the harness plug for corrosion, and visually inspect the unit for any obvious damage to the wires if you haven't already. i thought i had a test procedure for MAF's lying around in my links somewhere, but can't find it (it figures). hmmm . . .I'll have to dig around a bit more.

good luck - this is one of the most vexing problems on these trucks in my opinion.

cheers, and welcome to the forum -

isaac / seattle
'91 RRC
 

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Discussion Starter · #10 ·
Thanks for your input guys!
Searover, and deathorglory especially.
I had already checked the hoses coming from the crankase filter and did find it neccessary to clean them,the "tee" literaly snapped off in my fingers and was gummed completly shut.
This however didn't fix the problem.
I pulled the MAFS out of the truck and cleaned it paying close attention to the contacts at the connection (corrosion does seem to be an issue with these). This may have been the cure (for now) as it seems to run really well now.
The real test will e when I let the wife drive it ( it always dies on her!:) , ad I'm miles away @ work.)

Mike I have'nt seen your sawzall:D you still got pics of my series? post'em for Briggs.

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Ryan,

Don't let Lucas give you any crap, he has my sawzall and I'm just trying to get it back.

I've been keeping the pics of your frame secret, I didn't know if you were wanting to let the cat out of the bag, so to speak.

Do you want me to just send them to Briggs or post them here?

:D
 
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