Loss of power, bad or no idle intermittent

Suddenly, loss of power, dies, low or no idle. Next day all is good till she gets halfway to work then suddenly its bad again. It's intermittent, more prevalent when engine is hot.
Girlfriends Taco is 97 2.4 liter. Threw codes P0100, P0101, and P0420 .

The rear O2 sensor has less than 3000 miles on it.

I cleaned the MAF sensor with correct cleaner, no difference. I pushed on the throttle cable connector in an attempt to rev the engine and noticed that the engine stumbled. Fiddled with the throttle shaft and observed that if I open the throttle about 1 to 3 degrees of rotation the engine will die. If I open more than this it stumbles but then revs up.

Any ideas where I should start? I want to check the TPS but do not know what size of thickness gage that they are using for the intermediate measurement in the Toyota repair manual.

 

If it runs fine when cool, then I would check all your temp sensors.
P0100 and P0101 indicate a faulty MAF sensor (which doubles as a temp sensor).
The 0420 might be a secondary code triggered by the primary code(s).

There are other temp sensors that you can check the resistance of.
Not sure if you can check the resistance of the MAF.
If you have a buddy with a similar truck with the same MAF, you could temporarity swap it in to see if it helps.

 

The p0100 and 101 codes are MAF sensor codes, I haven't come across a MAF code that wast caused be the MAF... the p0420 (cat efficiency) code is more than likely there because the MAF readings are messed up. May also be MAF wiring. Check the wires from the MAF, make sure theres no nicks, chew marks from mice, or anything else. Cleaning a MAF usually doesnt help, especially one that is actually setting MAF codes, I see MAFs go bad and setting nothing but a lean code, if a MAF code comes up then theirs some serious problems with the MAF or its circuit. Only way to be 100% sure is to have a scan tool and watch the MAF reading at idle. Resistance tests will get you no where with a MAF, toyota doesnt give resistance specs for MAF, only voltage you should see at the MAF wire harness.

 

I would Ike to say that I misunderstood the description of symptoms. Here is a revised list of them. They occurred suddenly
1. Runs rough all the time.
2. Runs worse after sitting for 8 or more hours.

New TPS did not help.

 

Engine data would be very important in diagnosing the problem. The P0420 is most likely a result of the CAT not being able to run efficiently. A rough running engine usually means too much unburned fuel, etc getting into your cat, and the cat is unable to do its job.
MAF sensors can be tested for accuracy if you have access to a code reader that gives you small data. Examine your MAF sensor data at proper RPM to determine accuracy. In order to do this, you use the formula for MAF sensors for ICE systems in gallons per minute with RPM at 4000:
RPM over 4k--- RPM/1000 * engine size(liters) * number of cylinders
So for a 4.0 V6 at 4k RPM, you would expect 4000/1000 * 4 * 4= GPS or 64GPM.

 

While driving the truck I see that the timing never changes from 5 BTDC, even when hammering the throttle from idling in 5th gear.

The Fuel SYS1 displays OL not ready CL


Fuel Trims Long and Short both display 0%.

I am guessing that the engine is not going to open loop for some reason. I plugged into my truck and it hits open loop just a few seconds after startup.


Girlfriend is getting kinda itchy to have it running right. That make me have discomfort in my backside.

 

now I'm not sure about this, but let me toss this out there, not sure which 4 cylinder, could it be a crack exhaust manifold? I know its somewhat a problem with some of the 4 bangers.

 

Funny that you should suggest that one and it's not that much of a reach. I had to change the one on my truck right after I bought the truck.
I had suspected that she had a crack in the manifold so I replaced it just prior to my last post. I installed the 01 to 04 stainless tube exhaust manifold that I ordered from Toyota of Dallas. Funny, I've changed four of em now and this is the first one that was actually NOT cracked. I guess I'll sell it to somebody.
Anyways, the different exhaust manifold did nothing to address the problem that I am chasing.

I appreciated the input though, keep those possibilities coming folks.

Since I received my ODBII scanner yesterday I am learning how to use it and I must say that there is a lot of info available in the live feedback while driving. I do not think that the MAF is showing up but this may be due to the truck not obtaining closed loop operation.
Or, perhaps it will not hit closed loop because there is something wrong in the MAF circuit. I have more reading to do but please feel free to speed things up for me.

 

Coolant temp sensor.

 

I will try that again since it has come up in several formats. I changed it once (AutoZone part) and it made no difference in that way that it ran, but, it could have been a bad part. I say that since I remember now that my girlfriend said that the temp guage quit working after I installed it. Yes, it was definitely plugged in tight. Since I have had other problems with compatibility of Autozone parts, I should have tried another stores product right then.

 

yeah, when it comes to ordering just about any sensor, or the O2 SENSORS,
it might take a few days, but you just cannot beat rockauto prices. and they will carry the oem's. always try to stick with something that came out of japan, avoid the crap that comes out of China.
(how do i know, from 2001-2008 i traveled and worked there. and i have seen it all.)

yeah i know more about the 3.4, but man, i used to love to help my dad and grandad, work on their toyota 22r's when they had them, years ago.
that was one of the best motors ever built by man.

 

Well folks, I changed out the coolant temp sensor, cleared the codes with the scanner, unhooked the battery for half hour. Re installed battery, hooked up scanner turned on key and immediately got a code P0100. Started vehicle and let it warm up. It never hit closed loop and after 5 minutes of idle the code P0101 came back.

Running out of options and its looking like the $120 MAF is next on the list...

 

Here are pics of the ODBII scantool with the truck idling.

 

Just to play it safe, check your wiring for a chaffed wire along the MAF sensor, then look at the terminals of the connector. What you want to see is a tight, clean terminal for each one. If one or more look like they may be "stretched" a little open, or the terminals do not look clean and consistent, you may want to consider replacing a terminal, or getting a new connector pigtail. That being said, if all terminals look good, you may be looking at a MAF sensor. Though I would also suggest you check to make sure there are no vacuum leaks or signs of a cracked or broken hose in the intake stream after the MAF sensor.

 

Bill is the MAN!! He pointed me in the proper direction and the girlfriends TACO is healed.

 

So ... what exactly did you do to correct the problem?
Bill mentioned several things to check.

 

What finally did the fix was a new MAF sensor. I apologize to all who may have been watching with interest for not posting the "fix". We have picked up an additional code, P0171 now but the truck is running so much better. Will post progress on this issue.

 

You have an O2 sensor maxed out on the rich side and it is unable to compensate for it.

 

The GF is complaining about the truck again. Was running good for a while but now is down on power again. I plugged in the OBD2 scanner again. Found the following:

Short term fuel trim is usually in the +12 to +22 range although it does occasionally come close to zero while coasting in gear.

Long term fuel trim is usually stuck at +22 but has ventured up to +35 while accelerating.

The front and rear O2's are both showing very low voltage output.

The MAF does not show as much airflow as I think it should.

While at load and driving it will go into closed loop but when it sits at idle it goes to open loop.

Any ideas on this anyone?