ThePlumber

First time poster-longtime watcher & reader. Plumber by trade if I can help.

I've checked many threads and this link also. http://www.4crawler.com/4x4/CheapTri...ottleStopScrew

My 1994 Toyota 3VZE is exhibiting the symptoms of the TPS gone bad or out of adjustment.

I have one dumb question (with more to follow probably):

Where is the Throttle Stop Screw and must it be adjusted with the engine running before adjusting the TPS?

P.S. I know this a Japanese logo but as a plumber all I think is a jovial nightmare of dancing poo.

Thanks.

Jay351

The throttle stop screw is on the butterfly,beside the throttle cable. ITs clearly visable.

You shouldnt really ever have to touch the throttle stop screw unless sombody messed with it. Can be adjusted off, just a bolt that stops the butterfly from closing all the way.

ThePlumber

Thanks for the reply. Next question:

There is another "stop screw" located opposite the TPS. A lever is there that when the engine is running or off (can't remember) the screw will come in contact with what appears to be a plunger moved by vacuum. Is there a test and adjustment for this screw?

I'll take some pics tomorrow if needed.

Thanks.

ThePlumber

Jay351

Thats the dashpot. It slows the throttle plate down when you let off the throttle to keep it running smooth (and I think it serves an emissions purpose but I can't remember).

The dashpot should move smoothly and cusion the throttle plate as it closes.

abecedarian

that'd be the dashpot. keeps the throttle from closing too quickly.

abecedarian

IIRC, if you pinch the hose closed while the throttle is opened, then release the throttle, the engine RPM's should hold around 2000 and when you release the pinch on the hose, it should settle to idle within a second or so. If it doesn't hold the rpms properly, the diaphragm is bad, etc.

ThePlumber

Thanks for all the help.

Here's a few pics I snapped to reconfirm that I've given you the right information.

The first pic is kinda' dark. Wondering what the black plastic device is that's also operated with vacuum. Located on the front side of the TB near the oil cap. The other one, as you can see is connected to the TPS mounting body. It touches the adjustable screw with jam nut. Does it ever need adjusting?

Thanks.

ThePlumber

Jay351

The first picture is of the dashpot, not sure of the second one. I dont have that on my rig..

TNRabbit

The second pic is the cold idle adjustment.

ThePlumber

Cold Idle Adjustment Screw. Thanks TNRabbit.

Many things to do. When I get the driveability to stop being temperamental, then I've got to redo the exhaust. Brackets just gone. Exhaust has holes and there getting bigger/more of them by the day.

Holding it together with plumbing parts.

235,000 miles and holding.....

ThePlumber

TNRabbit

Third pic is the Cold Idle Adjustment, too, from the backside....

ThePlumber

Some more info about what I'm trying to figure out and welcome all opinions.

Details:

1994 Toyota PU Ext Cab 4WD.
3VZE Engine.
Around 235,000 miles.
Head Gaskets redone and valves reset at about 140,000 miles.
No apparent problems with head gaskets to this day. Don't see oil in coolant or coolant in oil.
Good power-for the 3.0 of course. Pulls strong in 3rd up to 50+mph.
Uses/leaks some oil. I don't keep a good record of the average loss.

Problem:

I get a hesitation or "stutter" under partial throttle. Traveling on flat road, keeping the truck at 50mph, you can feel it.

I've checked:

VSV to the EGR. Works fine applying 12V.

Throttle Position Switch with a meter and this link. http://www.4crawler.com/4x4/CheapTri...ottleStopScrew Within specs.

Sprayed carb cleaner around all vacuum areas while running. No skip or stutter at all.

Replaced the EGR valve. Cleaned all areas and passageways thoroughly.The temperature sensor is connected.

Replaced the coolant temperature sensor.

Replaced the vacuum modulator. The check engine light was on before I replaced this. I replaced it and it went off in about 5 miles of driving. I did not reset anything.

Replaced the fuel filter at about 180,000+ miles. Old one looked fine when cut open.

Doesn't feel fuel pump related. Pulls strong throughout when under throttle load.

No restriction at the exhaust system. I've been underneath while it's running and also have patches on it as there are many leaks. (Exit of the cat, the mufflers pinholed, the end pipe is half gone. Exhaust appears to be pushing everywhere. Next.

Wires and plugs replaced.

Throttle body clean.

Air filter clean.

The ECM had two codes stored in it. 14 and 71. http://www.ncttora.com/fsm/1993/engine/85diagnosi.pdf pages 7 and 8.

I have since reset the codes, driven it a few miles, and no codes are now present.

Hesitation/stutter still there. Where would you test and/or replace next???

Thanks for all input.

ThePlumber

BoostinChick

Code 71 is a malfunction in the EGR system. Did you tighten all the bolts and double check your vacuum hoses related to the EGR all the way to the VSV?

https://www.yotatech.com/forums/f116.../#post51141054

ThePlumber

I did. But I will check again as I can definitely make a mistake.

Thanks for the reply.

ThePlumber.

ThePlumber

Now I have checked all bolts and connections. The EGR is very stable and all connections are tight.

I traced lines from the EGR Valve to the EGR VSV to be correct and open.

Thanks.

ThePlumber.

ThePlumber

I remove the EFI fuse to clear codes. I bridged/connected the TE1 and E1 terminals to confirm this. No CEL, no codes.

Then I bridged the TE2 and E1 and performed the EGR driving test.

Returned, and bridged the TE1 and E1 and codes 14 and 71 are again stored.

However, no CEL.

Giving you all the information I have as I'm sure I'm confused.

ThePlumber.

TNRabbit

Sounds electrical; is it only under load or does it happen when you rev up under light throttle or hold steady throttle @ 2k rpm?

I'd bet distributor electrical issue, or you have a bad contact somewhere in the wiring harness. They're getting old now and the heat takes it's toll on wiring.....

ThePlumber

No tach, so I can't get real specific on RPM's. Sorry.

I honestly do not feel it if sitting still under partial throttle. Feels reasonably smooth.

Also, does not show any trouble when flooring it through the gears.

The most prevalent time is when I'm in 5th and driving 50mph or lower under partial throttle. About 1/4th to 1/5th of the pedal travel.

ThePlumber.

ThePlumber

CORRECTION.

I told you wrong. I azz-u-med it was smoother sitting and pressing the gas pedal at about 2,000 rpm.

I was wrong.

Once again, no tach, but sitting still, under partial throttle at a certain "sweet spot" I can get the engine to really lope up and down hard. I'm holding the pedal rock steady and the engine feels like it is going from idle to +-2,000rpm in about a 2 second cycle between the two. Up, down, up, down.

Go past it, smooths out. Leave it alone, idles fine.

Thanks for reading and all suggestions.

ThePlumber.

ThePlumber

Any other ideas before I'm off to the local dealer? My independent mechanic unfortunately has had personal problems and has disappeared.

Thanks.

ThePlumber.