Tigerstripe40

This started recently.

I am getting a random stumble on my 3VZ-E.

Occasionally, the engine will stumble. It's almost as if it stops. I get a 'buck' from the engine, the RPMs drop to zero, the check engine light comes on for a split second, then the rpms will jump back up to 1000 (or wherever it was) and the engine runs as if nothing is wrong.

I've noticed it mostly when the motor is cold and not to operating temp. However, it's happened once or twice while I was on the freeway, and the motor was at the proper operating temp.

There are no trouble codes stored.
However, I think it might have something to do with the ISR mod I did recently. The pipe is perfectly sealed. I sprayed all of the junctions with starter fluid with the engine running and dind't get an idle bump.

Any ideas?

funjumper

My 3vze in a '94 4runner just blew the head gasket after having similar symptoms. I didn't get a mix of coolant/oil. I got coolant out the exhaust and bubbling coolant out the radiator overflow.

How many miles on your motor? When was the last time the head gasket was replaced, if ever?

Tigerstripe40

Motor has 700 miles on it.
I did a full rebuild of the engine with all new OEM parts.

rdharper

Have you checked or replaced the AFM? I had symptoms similar to yours on my 22re at about 200k miles. Got worse, traced it to the phenolic wearing through under the wiper in the AFM. Tried fixing it, but eventually replaced it.

I believe my '94 3vze has the same AFM, although no problems so far with it.

What happens is because the phenolic wears through at some point, false information gets back to the ECU at different angular displacements of the air gate which it monitors.

Tigerstripe40

The AFM is original with 230,000 miles on it...

I will take a look at the AFM tonight.
Thanks for the tip

Chapman88SR5

mine does the same thing until its warmed up then it runs just fine. where could i get a new afm?

Tigerstripe40

The dealership.

check this out:
Champion Toyota

edit:
Just saw the price on the thing
HOLY CRAP!

check out www.car-part.com
you can search most of the junkyards in the country for stuff.
Looks like you can get one for about $75 + shipping

Chapman88SR5

yeah.... anywhere else. too much money

rdharper

The dealer wants $700, and that was back in 2000. But there is no reason you can't pick up one much cheaper if you search around.

There is a test procedure in the FSM which requires only an ohmeter. You can reach the gate.. If you move it, the ohms should change smoothly which mine did not. You can also open up the cover held in place with RTV, which I also did. That confirmed the problem, you could see the wear on the brown phenolic. As I said, couldn't fix it, but I was able to make it work well enough to drive the truck for awhile before the problem came back.. so I gave up and replaced it.

I peeked at Ebay, this link shows a used AFM for a buy-it-now price of $75.
Since the wear is predictable, its hard to say how long that would last. But it might be a way to get around doing the ohmeter checks.
Here is the link if you want to check it: http://cgi.ebay.com/ebaymotors/89-95...spagenameZWDVW

TexJJ

Wow, hate to say it, but sounds like a problem I have been trying to find for over a year. The only thing you have changed since the jerk is the ISR mod? Maybe there is a clue there.

JJ

Tigerstripe40

I was testing the AFM module last night with my meter and I noticed something.

I didn't clamp down the battery terminals when I put the motor back in.
Clamped those back down and I will see how things go.

rdharper

If you mean you didn't tighten the clamps on the battery posts, you make me laugh (just a bit). Anyone that has the skill and nerve to replace an engine, then forgets to tighten the battery...

If it were loose enough to be intermittent, it could cause a stumble, hiccup etc. If the clamps were clean, chances are you will still have your symptoms.

Let us know.

Tigerstripe40

Yeah, story of my life.
I have no problem tearing into the engine, or a transmission, but tightening the alternator belt on the 3VZ took me a while to figure out.
:pat:

Yes, the clamps are clean, so I am not 100% certain that is the problem. Just going through little things until I get it figured out.

Tigerstripe40

Where is this Phenolic piece?
I popped the VAFM out and looked at it.
No Phenolic.
Just aluminum.

Is this underneath the cover that is siliconed shut?

rpeAMP

Definitely sounds electrical to me. Check your engine grounds and also your alternator. Sometimes if it's going in and out, the engine will die due to the erratic shifts in voltage.

I wouldn't just run out and buy a VAFM just yet, but if you do get one, check out NAPA. They sell a remanufactured one for nothing compared to what the dealer wants for it. I have one in my truck and it runs just fine.

Tigerstripe40

I think it was the loose battery clamps.
Since I tightend those down, I haven't had any problems.

I did test the VAFM, and electrically at least, it's good.

rdharper

Yes, in the sealed part. The pickup moves with the gate, on the phenolic. The resistance varies as a function of the angular displacement of the gate.

I wouldn't open it unless I was pretty sure the AFM is not working correctly.

In my case, I'd swing the gate slowly, and would see a jump in resistance at various points. This was caused by wear on the phenolic causing intermittent discontinuties.

If you got correct readings according to the FSM, then its time to look for another theory. And you've saved a good bit of money, and learned something!

Tigerstripe40

Took the 4Runner out today.
This is the first trip on it, and really the first time I've had it in 4Low.

Truck performed almost flawlessly.
Has GREAT power for climbing hills, and keeping the speed up on the freeway. IT also handles mild obstacles with ease.

But I said almost flawlessly.
The stumble is still there.
IT happened 5 times today.
3 times on the freeway with the Cruise Control set.
1 time on the trail.
1 time while the truck was sitting there idling.

In all cases the SAME Thing happened. The engine stumbled. Dropped to zero RPM's the CEL flashed, then the RPMS jumped back up to where they were supposed to be and everything was fine.
No codes in the computer.

Could there have been a wire in the Engine Wire assembly that got cracked when I yanked the motor??

Would a bad O2 sensor do this without throwing an O2 sensor code?

rdharper

Have you tried pulling stored codes? May or may not provide a clue, but it can't hurt to see what they are.

Tigerstripe40

One of the first things I tried, actually.

There aren't any.
This thing is really tickign me off.

I am into this motor $3000 at least, and it shouldn't be doing this.
IT's getting to the point where I want to drive it out to the desert, burn it to the ground, and drive my relic FJ40.