redvette1986

I am a tad out of my league when it comes to MAF...which the manual says is what a code 34 means. Here are the symptoms:

Turn key, she fires right up as usual but 50% of the time she shuts right down with a SES light. When she does stay running she behaves as usual.

The only code showing is the 34. I am going to change the fuel filter cuz I have one and planned on it soon anyway.

What should I check relative to MAF...the connector looks good. Also, where is the MAF relay located? The car is a late 86 (alum. heads etc.).

Thanks

Corvette0096

I would change the relays first. There are two of them and they are on the firewall by the battery. If that is not the cure then you would have to change the MAF out. Make sure you disconect the battery to clear the codes. Here is a good web site that I go by.

http://www.c4vettes.com/ecm.htm

rick lambert

I agree with checking the relays first cause there cheap.But before you think about replacing the MAF, start by checking terminal C on the MAF sensor, it should be about 0.5 volts at idle and 4.7 volts at WOT.Alot of the time it just comes down to the throttle body having carbon buildup-and it needs to be cleaned, Chevy bulletin number 87-100, 85-87's. Also look to see if you have any cracks in the air duct.

Here's a test. Unplug the battery for at least 10 seconds to clear the code. Next, unplug the MAF sensor and start the engine, run it in park or neutral @ 2300 rpm's for a minute or until the service engine light appears-if you now have a code 33 you have a faulty MAF sensor. If the service engine light does not come on you might have a shorted ground 998 (dark green wire) coming from the MAF sensor or a faulty ECM. I'm betting on a carbon build up in the throttle body.

redvette1986

Thanks for the comments guys. I will try the test that you mentioned however I keep my throttle body way clean. I did it maybe 6-7 weeks ago. At this point changing the fuel filter is all I have done and the problem appears to have gone away. I cleared the code and so far no SES. Idle seems more stable now too!

rick lambert

Well if you removed the throttle body and CLEANED it, how about the IAC and housing? did you clean that also? sometimes it can cause all kinds of crap!

SilverBeast

Yeah. That IAC chamber is a carbon magnet.

redvette1986

Nope...didn't do anything with the IAC. Not even sure what to look for there. Where is it and what does it look like...BTW, I got my code again but since replacing the fuel filter she isn't stalling anymore...could the symptoms be unrelated or is the ecm compensating?

rick lambert

The IAC is located on the throttle body, has if I remember right a electrical connection to a nut, unscrew it,there's a gasket then a somewhat pointed valve (called the pintel) this should measure 28mm from the end of the pintel to the flange of the body without the gasket, if it's more or less, adjust it. Bottom line-clean it. Hope this helps. By the way, if your looking from the front of the car at the TB, it's on the passenger side on the lower part of the TB.

JrRifleCoach

Last week I had a MAF burn relay failure. The symptoms were not even close to a MAF. Just filled the tank and made it about 6 minutes down the road. Engine quit running. Pulled over to restart and she would start and run at about 1500 RPM, no more, no less, with help from the throttle. So I pulled the MAF connector and drove her home (30 Miles) without event.

Pulled codes with a 34 & 36. Replaced both relays, cleared codes and test drive. No codes....running as before

-JRC-

redvette1986

Ok...Is there a "humble-I-feel-like-a-putz" icon?
I just checked the throttle body and it was black as hell! I guess my sense of timing is off. Did I say 6-7 weeks ago it was cleaned?

NOW it is clean...again, cleared codes and the SES hasn't lit up yet. Took it around the block and so far so good...I'll keep ya posted.

rick lambert

Great-hope that solved the problem-if it did-great if it comes back-do the IAC.

redvette1986

Code 34 came back...

The IAC is now clean...but the end of pintel to flange dimension is 29.31 mm. Is this within tolerance? You said 28...and I see no way to adjust this dimension...

Edit... I just figured out how to change the length by turning the post.

redvette1986

REGROUP -

Sunday:
1. Car began to shut down at start up intermitently (50% of the time).
2. First SES light in years appears.
3. Code 34 found. Book says fuel filter or MAF.
4. I change FF and she is good for about 4 hours - no code / no stall.

Monday:
1. Car lights up SES first try in the morning - code 34 again - stalling no longer a symptom.
2. I clean throttle body without disassembling.
3. No codes for several hours.
4. Later that night I get a code 34 again.

Tuesday:
1. Drive 40 miles and get SES seconds immediately after starting up. ...plus a brand new symptom...wild idle. At traffic lights idle is 1500 - 2000 rpm in neutral. Intermitent - at some lights she returns to 650 rpm (normal).
2. I inspect relays near battery and one has 3 wires all bare insulation.
3. Fixed insulation - cleared codes - start up and I get SES light again. Code 34.
4. Disassemble throttle body and clean the hell out of both the intake and IAC/housing. Adjusted pintel to 28mm. Reassemble.
5. Clear codes and restart - SES and code 34.
6. Did Rick's "unplug maf sensor" test (above) and guess what...code 33

Corvette 0096's link shows the following for a code 33:
(1985-1990) Inspect intake system for leaks, Inspect for vacuum leaks, Check MAF connector and wiring, Check MAF for open using digital Ohm meter. Possible ECM failure.

BUT...since the test was done with connector off, isn't this what SHOULD have happened? And why didn't I get the old code 34 also?

Duf

Hmmm my 88 just started throwing a 22 and a 33 error. I have never messed with any intake aspects of the car as of yet so I will be following this thread closely. Hell I don't even know how to clean the TB.

redvette1986

REGROUP -

Sunday:
1. Car began to shut down at start up intermitently (50% of the time).
2. First SES light in years appears.
3. Code 34 found. Book says fuel filter or MAF.
4. I change FF and she is good for about 4 hours - no code / no stall.

Monday:
1. Car lights up SES first try in the morning - code 34 again - stalling no longer a symptom.
2. I clean throttle body without disassembling.
3. No codes for several hours.
4. Later that night I get a code 34 again.

Tuesday:
1. Drive 40 miles and get SES seconds immediately after starting up. ...plus a brand new symptom...wild idle. At traffic lights idle is 1500 - 2000 rpm in neutral. Intermitent - at some lights she returns to 650 rpm (normal).
2. I inspect relays near battery and one has 3 wires all bare insulation.
3. Fixed insulation - cleared codes - start up and I get SES light again. Code 34.
4. Disassemble throttle body and clean the hell out of both the intake and IAC/housing. Adjusted pintel to 28mm. Reassemble.
5. Clear codes and restart - SES and code 34.
6. Did Rick's "unplug maf sensor" test (above) and guess what...code 33

Corvette 0096's link shows the following for a code 33:
(1985-1990) Inspect intake system for leaks, Inspect for vacuum leaks, Check MAF connector and wiring, Check MAF for open using digital Ohm meter. Possible ECM failure.

BUT...since the test was done with connector off, isn't this what SHOULD have happened? And why didn't I get the old code 34 also?

redvette1986

Turns out it was the MAF relay...not sure which one cuz I swapped out both. Still had a high idle but that is cuz I cleaned out the TB and IAC and didn't torque the TB back. It was twisting slightly and binding the butterfly shaft. Torqing to 18fp and a squirt of DW40 fixed the non-returning idle problem. All is now well and thanks everyone for your helpful advice and input.

I swear that without this forum, I would not be able to afford driving an older vette!