Help on my 1990 4Runner winter beater.

[channer]

Hi

Does anyone know what would cause a 1700-2200 RPM stumble/hesitation/shake in my 1990 Toyota 4Runner with a v6 & 5speed.

The hesitation is really noticable when I am justs cruising along in either 3rd, 4th or 5th gear... and once the tach hits 1700+ RPM. I usually have to downshift to a lower gear. It idles & runs fine under 1700 RPM or above 2200 RPM. When it shakes, the tach RPMs stay steady, it doesn't fluctuate!!!

The odd thing is the stumble/hesitation does not occur if I am going through the gears... or if I am at 1700 or lower RPM & step on the gas... it will rev through to 3000+ RPMs with no problems. And being in the GREAT WHITE NORTH, it does not stumble or hestitate at 2000+ RPM idle on cold starts either.

The hesitation does not happen all the time, but it is becoming more frequent. I've changed plugs, wires, rotor & cap, O2 and EGR but that hasn't made a difference!!!! There is also no code or engine light!!!

Any ideas, suggestions.

TIA....dave

 

[GNeric]

That is right about normal cruising RPM's and I would be willing to look into the black plastic top of the Vane Air Flow meter. The cover is "glued" in and you will have to cut the silicone glue out and check to see if the little contact has worn a spot in the portion of the meter that is right where the cruise RPM pulls to. You can have the engine running and open the throttle to that point and watch where the stumble happens and carefully clean the black portion of the meter with a Qtip and Isopropyl alcohol. If the meter is bad, they run near $800 to replace from the Dealer. We have had some come in with A1Cardone meters that aren't correct. Kind of like the MAF's that are remanufactured for the GNs. Never quite right. Hope this helps.

 

[channer]

Thanks Eric

Never thought about the airflow meter. I picked up an ECU last weekend at the UPIC yard... I'll go back for the airflow meter.

I picked up an ECU last weekend at the UPIC yard... I'll go back for the airflow meter this weekend & swap it out to see if it makes a difference.

dave

 

[topfuel]

I'll bet you have clogged EGR ports inside the intake manifold.
Each cylinder has it's own narrow EGR passage which can become
clogged with carbon. Eventually carbon will clog all but one or two passages,
and send all the EGR to those one or two cylinders causing them to
misfire at exactly the RPM range you described.

I've seen this problem hundreds on times on Hondas and Acuras
when I worked for them.

Try disabling the EGR and see if the problem goes away.

 

[GNeric]

Would be cheaper to check yours before buying another AF meter. Even junkyard ones can have the same symptoms as yours so it would be a waste of money until you make sure yours is clean first. If you clean yours and no difference or yours is damaged, then go get the one from the yard. You could also disable the EGR like Topfuel said, but these do have problems with the AF meters. Always do the cheap/free checks before spending money.

Thanks Eric

Never thought about the airflow meter. I picked up an ECU last weekend at the UPIC yard... I'll go back for the airflow meter.

I picked up an ECU last weekend at the UPIC yard... I'll go back for the airflow meter this weekend & swap it out to see if it makes a difference.

dave

 

[channer]

Hi

I took a look at the air flow meter. Debated on taking the plastic off!!! For $20-25, I rather have a backup should I screw something up & be car-less. Besides, the UPIC yard offers a 90 day return policy.


how do I disable the EGR? It's vacuum operated like our Buick.

The EGR is basically one tube that goes into the intake manifold. Is this the EGR port you are talking about or is there another location for the EGR port?

TIA... again

dave

 

[topfuel]

Hi

how do I disable the EGR? It's vacuum operated like our Buick.

The EGR is basically one tube that goes into the intake manifold. Is this the EGR port you are talking about or is there another location for the EGR port?

TIA... again

dave

Remove the vacuum line and plug it, see if it runs better then.

 

[TURBOTWIN2]

I would check to see if the throttle body is dirty, behind the throttle plate (flapper). You can clean it with a rag a carb cleaner. Also the Throttle Position sensor (TPS) can have a bad spot right there where it rides at cruise speed. A tech with a lab scope might be able to catch what ordinarily would be hard to diagnose, this one's tricky.
You can check for ECM codes manually, jumper wire to E & E1 at the underhood ALDL connector under the hood and count the flashing "check engine" light on the dash. Google how to scan your vehicle to verify the connectors and code descriptions, as I'm going off memory.
HTH.

 

[channer]

Wouldn't you know it... start the new year & the car runs fine... no hesitation, no stumble in two days

Anyways, I got & installed another airflow meter from the UPIC yard for $30 (price has gone up). I also cleaned the TB, it wasn't too dirty/oily and checked for codes... no codes, just a constant blinking.

Took the truck for a long spin, checked for codes again... nothing.

I'll give it a couple more days... I'll put back my old airflow meter & see what happens!!!

thanks all... dave