DS223

First post to YotaTech. I have a 1994 pickup with the 3VZ-E 3.0 V6. For the last two weeks Ive been replacing and doing general maintenance. I've changed the water pump, thermostate, timing belt, timing belt idlers, belts, Rad Hoses, coolant flush, plugs, cap, rotor, wires, and a K&N air cleaner. When i went to time the motor jumping terminals TE1 and E1 the mark was running about two inches to the right of the degree marks. so i left it alone. after taking a road trip I noticed the truck loses power up hills, and has a noticeable hessitation in the throttle. it also has a steady high idle (like 1500 at cold start the about 1200 the rest of the time). After a few hours of searching the threads i came acrossed the tps. looking at the diffrent syptomes people are having im having the same. No idle drop when connectors are jumped, hessitation, power up hills, and the timing. I read the TPS reports http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml I also unpluged it and it seemed to improve the throttle response around town.
after test my TPS i oreder a new BWD TPS. After compairing the old and new im getting about the same ohms from each. I have yet to put the new one on in hopes that if the old is good i can return it for the $97 back. any ideas would help. Also the intake hose has some cracks in it where it connects to the throttle body they dont look to be past the lip were the hose seats on the body, might this be a problem. thanks for the help

alltracman78

Vacuum leaks will definitely cause your engine to not run right.
However, if you have a high idle it's unlikely you have a vacuum leak [will lower the idle].
Your TPS may have been out of adjustment. Try adjusting it before you replace it.

BMcEL

Can you say power steering idle-up? A/C idle-up? Do you know what raises the idle speed?

Unmetered air AKA vacuum leaks.

alltracman78

No way man, the only time unmeter air raises idle is if the ECU uses a MAP sensor.
AFM/VAM, MAF both drop idle if you have a vacuum leak/unmetered air.
Pwr steering and AC idle ups both use metered air.

MudHippy

It depends...

A leaking air intake hose will lower the idle. Because it's going to lower vacuum pressure before the idle air bypass circuit(in the throttle body). Which will cause the VAFM to act as if less air is entering the engine. What actually happens is the vane/flap in the VAFM stays more closed than it should be because of the lack of sufficient vacuum(since it's leaking before the TB & the idle air bypass circuit, and not after). The more the vane/flap closes in the VAFM the less fuel will be delivered to the engine(because the ECU now thinks there's less air entering). Thereby lowering the idle speed. Less fuel, less rpm, more fuel, more rpm.



Only vacuum leaks AFTER the TB/idle air bypass circuit raise the engine's idle speed. Because it's effectively the same as opening the idle air bypass circuit wider(turning the idle speed adjusting screw counter-clockwise/in the outward direction).

alltracman78

A vacuum leak after the TB will do the exact same thing as a vacuum leak before the TB [but after the AFM].
It's still unmeasured air entering the engine.

BMcEL

My idle rises when introducing a small vacuum leak before the throttle body and after the VAFM. How's that work?

BMcEL

Where's the proof?

alltracman78

Follow dem vacuum lines.

DS223

This morning I reinstalled the old tps and adjusted it to spec. after the motor got to temp the idle has droped. it runs at a steady grand, 1200 after starting. still no idl drop after jumping the terminals. any Ideas? Thanks

MudHippy

Keyword: small

How? It's called idle mixture. There's a screw for that too(on the VAFM). So if you introduce a small enough leak in the intake air hose, it's the same as turning that screw outward and opening that circuit slightly wider(thus leaning the A/F ratio at idle). Up to a point the idle speed may raise, somewhat. But a large enough leak WILL lower the idle speed...GUARANTEED!

Still don't believe me? Cut a hole about the size of a dime in your air intake hose while the engine's running and watch what happens. Or simply pull the PCV breather hose next to the throttle body on a 3VZ-E while it's running(effectively the same thing as cutting a dime-sized hole in the air intake hose).

Hint: A large enough leak will even cause the VAFM to shut far enough to kill the fuel pump switch. Motor won't want to run at all then.
Wrong. If so then just how do the A/C or PS idle ups manage to raise the idle speed. Because of the fact that it's metered air? HAH! I think not. Disconnect the hoses for those from the air intake, plug the holes in the air intake, and let the hoses draw unfiltered/unmetered air instead. Does it make any difference in how the function? NOPE, NOT ONE BIT!!! They both still work exactly as they did before. Why? They ONLY need an AIR SOURCE(PREFERABLY FILTERED) to function correctly, NOT NECESSARILY METERED AIR. The fact that it is metered, under normal circumstances, is of no consequence.
Why don't you set the idle speed the way it's supposed to be set, @ 800 rpm +/- 50 rpm, and see how it runs then. What's with all this TPS adjustment if it's really needing the idle speed adjusted? You know there's reasons why the idle's set at a particular speed from the factory, and why it should always be adjusted to maintain that specified idle speed.

FYI, the idle speed NOT DROPPING when you short the check connectors means absolutely nothing. IT SHOULDN'T! But go right ahead and jump on that BS bandwagon if you must...

alltracman78

No way man. You need to relearn some of this stuff....
All the idle ups [including the ISC valve] raise the idle speed by bypassing the TB [but still using metered air], not by adding unmetered air in.
Disconnecting the hoses from the intake doesn't effect anything because the idle up valves are CLOSED normally......
So no unmetered air is getting past them.
Disconnecting those hoses is the same thing as drilling that 1/2" hole in the intake tubing you were talking about......

A vacuum leak in an AFM metered engine WILL worsen the idle, or kill the engine.

BMcEL

Of course idle will drop with a big enough vacuum leak. My point was that your first statement wasn't entirely correct, hence the rhetorical question.