[BamZipPow]

1996 T-100 auto 2WD with the 3rzfe 4 cylinder engine ran fine the night before. The next morning, the engine would fire and then sputter and die. Ultragauge got an immediate code of P0100 and P0505. I could smell that the engine was running lean but no codes were set fer a lean condition. It is unlikely that both sensors died but it could be possible. I had limited tools to work with in the middle of the night so I wasn't able to do any lengthy diagnostics. Removed the throttle body fer inspection as well as the IAC valve. Throttle body and air plenum was dirty but everything moved fine. Inspected the MAF sensor as well. MAF sensor didn't show anything visual issues.

According to this, it's most likely a vacuum leak after the throttle body butterfly plate. I did notice that the throttle body gasket was cracked and a few vacuum hoses were split. I will address those when I visit the strickened T-100 tomorrow morning.

https://www.yourmechanic.com/articl...dle-control-system-malfunction-by-jay-safford

"The most common problem is a vacuum line to one of the intake or throttle body ports."

 

[jabush]

Good luck! Interested in the outcome.

 

[BamZipPow]

Just so you know what the codes were:

https://www.obd-codes.com/p0100
Mass Air Flow (MAF) Circuit Malfunction

https://www.obd-codes.com/p0505
IAC Malfunction

 

[BamZipPow]

Parts...

This is the sensor and the housing:
22250
METER ASSY, INTAKE AIR FLOW
22250-75010
1
$988.58

Online dealership price is $594.
http://www.toyotapartsdeal.com/oem/toyota~meter~assy~intake~air~flow~22250-75010.html


22270
VALVE ASSY, IDLE SPEED CONTROL(FOR THLOTTLE BODY)
22270-75020 (08/1994 - 07/1995)
1
$458.91

Online dealership price is $224.
http://parts.toyotaofdallas.com/oe-toyota/2227075020

22270-75030 (08/1995 - )
1
$440.32

Online dealership price is $214.
http://www.toyotapartsdeal.com/oem/...ed~control~for~thlottle~body~22270-75030.html

Throttle body gasket
22271
GASKET, THROTTLE BODY
22271-75020
1
$2.69

Oreilly Auto Parts had the Fel-Pro 61079 fer about $2.40 as they were the only ones who had the gasket available.

Autozone carries the same gasket fer $1.50.
http://www.autozone.com/emission-co...asket/felpro-tbi-base-gasket/390573_345436_0/

 

[BamZipPow]

So here's the update.

Two vacuum hoses were cracked, one coming from the charcoal canister and going to the vacuum port just behind the throttle plate and the other vacuum hose coming from the power steering vacuum switch to one of the vacuum ports in front of the throttle plate. The throttle body gasket was hosed and was probably contributing to the vacuum leak issue. The cracked carbon canister hose was the other key vacuum leak. After replacing the vacuum hoses and throttle body gasket, the rough idle issue went away. I took the time before reassembly to clean the throttle body, butterfly valve, IAC valve, and as much of the intake manifold as I could with some throttle body spray cleaner. It was pretty gross.

Piccies!

















The code P0505 went away during the code reset using the Ultragauge to reset. The code P0100 stayed on after the reset. Monitoring the MAF on the Ultragauge, the reading was 0.510 g/s and never wavered up or down with the engine running and revved. The Ultragauge indicated that the ECU was running in open loop mode even after the engine came up to operating temp. I'm suspecting that the MAF is bad because of the airflow reading that I got. The wiring harness looked fine with a visual and physical inspection from the connector to where it went into the firewall. I did not check the connector going into the ECU nor did I trace the wiring as I didn't have my multimeter with me. I did cycle the connector into the sensor with no changes to the engine idle nor sensor readings. I even tried spraying the wires with MAF cleaner with no changes. The intake temp sensor did report the correct air temp.

Looking up on www.car-part.com fer local parts yards that might have a used MAF, I located one in Bryan that may have one fer $50 from a 1997 Tacoma. I'll see in the morning when I make a run out that way.

I did look up aftermarket MAFs on eBay and they seem to have a resistor wired in where one of the wires would be. Those were selling fer around $30 but I decided to pass on those.

 

[BamZipPow]

Talked to a SAE certified mechanic and he stated that with these codes, the job would have included replacing the MAF sensor, replacing the IAC valve and gasket, and replacing the throttle body gasket. Cost to do this job would have been well into $1400 at dealership MSRP and labor charges. Discovery and replacement of the bad vacuum lines would probably be tossed in fer free.

Cost fer me to replace the two vacuum lines and throttle body gasket was only $7. The MAF would only be the real significant cost to resolving the P0100 issue. Still better than forking out $1400+!

 

[Shaggyman]

MAF at Pick-n-Pull $36.00.
http://www.picknpull.com/part_pricing.aspx?LocationID=67&NavItem=11&SearchCriteria=&#partpricing

 

[noahrexion]

Did you try this Bam? I know you mentioned your ultragauge not showing anything - but checking it from the backside of connector while its running and plugged in like this would help eliminate any wiring in between obviously.

 

[BamZipPow]

"Shaggyma"
MAF at Pick-n-Pull $36.00.
http://www.picknpull.com/part_pricing.aspx?LocationID=67&NavItem=11&SearchCriteria=&#partpricing

Thanks! I'll keep that place in my back pocket if I need to find other parts sources. WWW.CAR-PART.COM has been my go to place when searching fer parts. The place out in Bryan, TX had the used MAF so I was able to pick it up fer $43 out the door. I'll find out later if this will git the 1996 T-100 back up and running. Too bad I can't find my multimeter so I can measure the resistance of the MAFs.

 

[BamZipPow]

"noahrexion"

"Did you try this Bam? I know you mentioned your ultragauge not showing anything - but checking it from the backside of connector while its running and plugged in like this would help eliminate any wiring in between obviously."

Yer image isn't showing up fer me but a quick check on the Internet reveals cleaning the MAF wires with a Q-tip and alcohol, right?

Yes, I've tried cleaning the sensor wires with MAF cleaner to no avail.

After the vacuum leaks were fixed and the engine started, I disconnected the MAF to see if the engine performance would change which it didn't. I didn't look at the UG display to see if the MA2 number disappeared or not but I will check and see before I swap in the replacement.

I've been wondering if the vacuum leak was so great that the MAF wire could've burned up due to the lack of air moving through it. I guess I could test the old MAF by blowing air past it and seeing if it detects the airflow or not.

If the replacement MAF resolves the issue, I will git some resistance measurements as well as some close up piccies of the wires before I start experimenting with the old part.

 

[BamZipPow]

Follow up...

Tested the theory of blowing on the sensor. No change in the reading.
Installed the replacement MAF with no change to the reading.
Got the bright idea of resetting the ECU to clear any issues from the vacuum leak. Normally when cleaning the MAF, one would reset the ECU. Reset the ECU by pulling the 15A EFI fuse located in the engine bay fuse box fer about 2 minutes. Using an OBDII reader to clear codes may not clear the fuel trims that the ECU has learned. Engine fired right up and no codes registered. When ever yer dealing with air/fuel issues, fix the vacuum leaks AND reset the ECU!

However, P0100 code came back in the morning.

Found my meter and measured the original sensor. Contacts (airflow arrow to the left):
1 + 2 = 3.73k ohms
1 + 3 = open
2 + 3 = open

Remeasured the sensor with the airflow arrow to the right (sensor upside down):
1 + 3 = 16m ohms
2 + 3 = 16m ohms

I measured both the top and bottom of the contacts with no changes to the readings with either position. I guess this would suggest that there are some contact issues with the sensor and the contacts. I'll have to see what the issue is with that (micro cracks, corrosion, etc).

I did clean the fusebox contacts fer the EFI fuse in the fuse box since there was some issues with those when it was popping them due to the clogged fuel filter issue from before. I didn't measure the actual voltage at the time going to through the EFI fuse referenced to fender ground or the battery ground as I didn't have my multimeter available at that time. I will have to do that later to see what that voltage actually is. The cleaning of the fuse contacts seems to have fixed the issue with the P0100 code. I'm guessing a low voltage issue can cause the ECU to have issues. I will have to measure the used replacement MAF sensor at a later time so I will have a reference to the old one.

 

[BamZipPow]

Since I had access to the 3rzfe T-100 tonight, I made some measurements.

Measurement on the replacement MAF sensor with the airflow arrow pointing to the left:

1 + 2 = 3.72k ohms
1 + 3 = 9.0m ohms
2 + 3 = 9.0m ohms

Voltage at the 15A EFI fuse with the engine running:

Supply to battery ground, 14.24 VDC
Fused to battery ground, 14.20 VDC
Supply to fender ground, 14.21VDC
Fused to fender ground, 14.17 VDC

The truck has been running fine since the replacement of the two compromised vacuum lines, replacement of the MAF, and cleaning up the 15A EFI fuse contacts.

 

[BamZipPow]

It's back...and the MAF reading is only reading a solid 0.505 and the ECU is running in open loop only.

Tracing wires to see if it might be a wire harness issue. I looked up the circuitry in my EWD and the diagram isn't exactly correct fer the 3rzfe engine. Fer example, it shows the same 5 wire MAF connector fer the 5vzfe and 3rzfe engines. The 3rzfe engine has a 3 wire connector fer the MAF.

I show a set of yellow/red stripe, brown, and white/red stripe wires going to the MAF. I believe the white/red stripe is supposed to provide 12VDC to the MAF and the other two wires go back to the ECU. I was able to trace the yellow/red stripe wire to the ECU. I still have to locate the proper brown wire to the ECU.

I'm guessing the MAF is not gitting the proper 12 volts. According to the EWD, power goes from the EFI fuse, through the EFI relay, through a split splice point (circuit opening relay), through a split splice point (+B to the ECU), an interconnecting splice (IE1) which then powers the MAF, IAC, +B to the engine bay data connector, and both O2 sensors. Hmmm, something tells me I need to look at IE1 which should be located behind the right kick panel. I should be able to test the +B in the engine bay connector fer 12 VDC to see if 12 VDC is gitting past that interconnecting splice which I'm guessing it's not.

 

[BamZipPow]

Pulled the engine bay fuse box and found that the wire from the EFI fuse was burned to bits. One wire had no insulation left on it and the other bigger gauge wire had half of it's insulation left.

Guess I'm buying a new/used fuse box or rewiring the burned wires with some new wire.

 

[SC T100]

That would have been tough to track down, but I'm glad it got diagnosed. Hopefully it was simple degradation, and not another issue.

 

[BamZipPow]

That would have been tough to track down, but I'm glad it got diagnosed. Hopefully it was simple degradation, and not another issue.

It was pretty easy to see once I started staring at the EWD and could tell that the common point with the MAF and IAC valve was the 12 VDC supply line. This issue came about from the time when the EFI kept blowing and ended up finding out that the fuel filter was clogged up which was causing high amperage on the fuel pump.

I will have to completely trace all the wiring from the EFi relay to each split splice point to see how bad the damage is and will probably repair it with the proper gauge wire.

 

[BamZipPow]

Carnage!


The white/ red stripe wire on the left is the supply line from the fuse to the relay and the blue wire on the right is activation line fer the relay.

 

[BamZipPow]

Made a little time to address the wiring by replacing both wires and got it all buttoned up. Turned the key to ON and no Check Engine light!

Started to trace the wiring again to make sure I was gitting voltage at the key points and decided to cycle the ECU connectors first. Presto! The last connector wasn't even plugged in! :surprise:

Plugged it back in and doubled checked everything one more time. Turned the key to ON and the Check Engine light was shining brightly! Time to go fer start! Took a few extra cranks but the engine fired right up. The engine was rattling a lot from the oil settling out over the past few months but it finally quieted down. The Ultragauge was showing good numbers fer the MAF and there wasn't a Check Engine light lit fer any codes. Whew!

So in summary, if you git a set code fer P0505 and P0100, chances are you might want to check 12V power to the MAF and IAC valve and hopefully yer EFI circuit isn't burned up.

This T-100 is ready fer a long drive now!