Bogging down under acceleration... MAF? Throttle Body? Something else? Asking for input (9 Viewers)

[67cruiser]

I have a limited amount of experience with this stuff, so I wanted some input from others with more experience...

Basics:

94 1FZ-FE 364,xxx miles - OBD1

I bought the truck with 307xxx miles and had not done any real engine work on it other than oil changes, tighten the throttle cable, and had the AC compressor replaced around 340xxx

Already have intermittent O2 sensor CEL... had stumbling idle on occasion and a slight hesitation on acceleration...

As a response to the rough idle and hesitation... in the last 2 weeks I replaced:

Fuel filter
Wires - NGK
Plugs - NGK Iridium
Cap - OEM
Rotor - OEM

Came back from Prairie City on Saturday - a fair bit of dust... got back into town and filled up fuel.

When I started the truck up, it was fine, but as I left the gas station, suddenly I felt a loss of power - UNLESS the RPM was in a very specific range of 1500 - 1800..... Couldn't really get it over 30 mph and I had to be very careful on the throttle - sometimes when I'd back off of the pedal, it would accelerate up to that rpm but would bog the moment I pressed harder on the pedal.

The next morning, it drove normal around town.

I did some research and it could possibly be a MAF sensor problem, so I bought some MAF sensor cleaner, and cleaned it.

It ran well again the next drive - but then the drive after that, it happened again - so I pulled the MAF sensor block again and cleaned and cleaned it. Still happened.

Codes read 24, 28 (already knew that), and 31....

Yesterday I grabbed the FSM from IH8MUD's Resources and tested the MAF sensor and the connector - all checked out - ECM voltage is there, Ohms were in range for the air temp.

It drove great to work yesterday.... I got some throttle body cleaner, I cleaned the throttle body well (didn't take it off of the intake manifold) - I let it idle up to temp - no CEL and idle was very smooth - between 650 and 700 without AC or a load on it. Drove great on the way home and the CEL came on at about 3 miles (basically my driveway) - same codes.

I haven't checked anything else around the throttle body.

This morning I cleared the codes - it ran fine for a half mile or so on the way to work - accelerated great..... then back to the limited RPM range - except now it's at about 1200 - 1400 RPM...

So I am at a loss... Has anyone here had a similar experience, and if so, what did you find the culprit to be?

Thanks in advance

 

[Toyo Boyo]

Sounds very similar to when my O2 sensor started failing.

Occasional stumbling on acceleration with a very limited rev range (around 1600rpm). This stumbling got more and more frequent but not every time I drove.

To test this, in P or N, rev the engine hard. I think the ECU ignores the O2 sensor in wide open throttle. It should rev freely at higher revs but then it’ll start to stumble at lower revs because it’s trying to use faulty inputs from the sensor (possibly confirming O2 issue).

 

[67cruiser]

Sounds very similar to when my O2 sensor started failing.

Occasional stumbling on acceleration with a very limited rev range (around 1600rpm). This stumbling got more and more frequent but not every time I drove.

To test this, in P or N, rev the engine hard. I think the ECU ignores the O2 sensor in wide open throttle. It should rev freely at higher revs but then it’ll start to stumble at lower revs because it’s trying to use faulty inputs from the sensor (possibly confirming O2 issue).

Thanks Toyo!

I will take a look at them -they should be replaced anyway.

However, when this is happening, the engine bogs in P and N as well..... so odd

 

[Toyo Boyo]

Are you able to get past the ’bogging’ and get it to rev past 4,000rpm? Or higher? And keep it there (for a short while anyways ).

 

[67cruiser]

Are you able to get past the ’bogging’ and get it to rev past 4,000rpm? Or higher? And keep it there (for a short while anyways ).

Toyo, I press down on the throttle pedal and it will rev up to that low RPM, and then stop going higher..... This seems to be intermittent.... It might not work tonight, but tomorrow it'll rev up just fine and then bog down a mile down the road.....

For instance, this morning it started and rev'd nicely to 4K without problem.... but bogged down on the way to work, and then 3 1/2 hours later during lunch, when I planned to limp it home, it didn't bog down and I drove it normally - albeit gently

 

[67cruiser]

Then, there's this guy - similar but not identical problems.....

RANDOM BOGGING DOWN?

So I've been chasing a problem with my 1994 Landcruiser randomly has problems accelerating from a stop, like from a red light, but only like once every 2 weeks. The truck doesn't seem to want to get over 10-15 mph, even if I floor it. I tried shifting from drive to neutral or 2 just to see if it...

forum.ih8mud.com

 

[LandLocked93]

Could be fuel pump, tho admittedly a very intermittent issue.

 

[67cruiser]

Could be fuel pump, tho admittedly a very intermittent issue.

I hadn't considered that.... Thank you...

I suppose a faulty new fuel filter could also cause headaches... - however, I did the filter before anything else and drove it about a week without problems until the other parts arrived.

The slight hesitation had been there a while and I thought it would go away with new wires and plugs, but it didn't.

 

[ToyotaDon]

Does the transmission seem to be shifting properly? Could you have also changed the position of the transmission throttle cable while tightening the main throttle cable?

If there was dust in the air, it would be a good idea to check the air filter. Also look into its inlet to be sure something larger like a plastic bag was not sucked up.

By the way, the '94 does not have a MAF, which would have a hot wire you can clean. Instead it uses a Vane Air Flow meter with the moveable vane, and cleaning doesn't really do any good.

 

[67cruiser]

Does the transmission seem to be shifting properly? Could you have also changed the position of the transmission throttle cable while tightening the main throttle cable?

If there was dust in the air, it would be a good idea to check the air filter. Also look into its inlet to be sure something larger like a plastic bag was not sucked up.

By the way, the '94 does not have a MAF, which would have a hot wire you can clean. Instead it uses a Vane Air Flow meter with the moveable vane, and cleaning doesn't really do any good.

Yep you're right. It's not a MAF technically.

I forgot to mention that I cleaned it the air filter.

Yes it seems to be shifting properly.

I can duplicate the bogging down when in park or neutral as well.

I appreciate all of the input.

I have a question though regarding the vane.

Is it passive? Changed and then measured by the airflow pulled by the TB?

Or is it active and controls at least some of the airflow to the TB?

 

[ppc]

I have a question though regarding the vane.

Is it passive? Changed and then measured by the airflow pulled by the TB?

Or is it active and controls at least some of the airflow to the TB?

The VAF is what you term as passive device. It measures the amount of air passing through it and the temperature of that air.

The active devices are the throttle plate, and the IAC - Idle Air Control in the throttle body. Another sensor to be examining for proper operation and adjustment is the throttle position sensor attached to the throttle body.

 

[ToyotaDon]

The VAF is what you term as passive device. It measures the amount of air passing through it and the temperature of that air.

This is correct. Almost all components connected to the computer are either sensors (inputs) or actuators (outputs). A few act as both, such as the Electronic Throttle Control throttle body on a newer vehicle, and that is really just several components rolled into one. The VAF and MAF are typically more than one sensor in the same housing, measuring airflow and temperature to determine the density of the air charge. In this case, they are sending more than one signal back to the computer on separate wires.

To the original issue: It sounds like there is either a lack of fuel or a lack of air, or the incorrect indication of one of those. The VAF would indicate the amount of air, and the computer adds the right amount of fuel. Other sensors affect how much fuel is injected, including Engine Coolant Temperature, Throttle Position, and exhaust Oxygen content. Though not as common with an intermittent issue, exhaust blockage is also something to keep in mind.

 

[67cruiser]

Thanks guys!

 

[landtank]

Get rid of the iridium plugs.

 

[67cruiser]

Get rid of the iridium plugs.

Tell me more.....

 

[landtank]

Tell me more.....

Take them out, throw them in the trash can and then install the proper plugs.

 

[White Stripe]

How much fuel pressure do you have?

 

[67cruiser]

How much fuel pressure do you have?

That's a good question.

I do not know how to measure that.

However, when I first start the truck, it accelerates fine in park and often I don't have a problem driving it around town, then randomly I suddenly have the problem a half mile down the road.

How does one check the fuel pressure?

I

 

[White Stripe]

That's a good question.

I do not know how to measure that.

However, when I first start the truck, it accelerates fine in park and often I don't have a problem driving it around town, then randomly I suddenly have the problem a half mile down the road.

How does one check the fuel pressure?

I

You'll have to get a fuel pressure gauge with adapters. Then temporarily mount it, and drive around while monitoring the pressure. Should be some write ups on mud on how to do it. Also in my opinion a wideband air fuel ratio gauge is a great additional permanent gauge to add to the dash of pre 95 land cruisers.

 

[67cruiser]

You'll have to get a fuel pressure gauge with adapters. Then temporarily mount it, and drive around while monitoring the pressure. Should be some write ups on mud on how to do it. Also in my opinion a wideband air fuel ratio gauge is a great additional permanent gauge to add to the dash of pre 95 land cruisers.

I'll have to learn how to do that