thook

This has been an intermittent/recurring problem that I thought was fixed long ago, yet........IT'S BACK!!!!!!!! This time the gun is loaded and if I don't shoot myself first, this thing is going to look like a long block of swiss cheese...

I can't figure it out and I'm hoping someone has had the very same experience.

Let me give you the run down:

Timing is perfect
New plugs
Good wires (tested them)
New fuel press. regulator
Fuel press. is good
New TPS adjusted correctly
No vaccum leaks....NONE
New coolant temp sensor
VAM is fine
Lots of things I've checked already, but ask anyway

Here's what it's doing:
It does it "mostly" when it's up to or close to operating temps. A couple of times (not sure how many....don't keep count) it has done when it's cold, but has gotten "better" in that respect the more I tinker with it.
It will idle just fine and quite normally (as in, it idles high and then slows as it warms and will idle evenly once it is..."mostly") until I press the throttle and release it. The idle/RPM seesaws and then it about falls flat on it's face and dies. It doesn't die everytime, but a lot.

If someone can help me figure this out and get it fixed, I may go ahead shoot the thing anyway just to relieve myself.....

thook

Incidentally, I messed with the dashpot. Meaning, I tested it and I believe it to be bad....not sure. I bought what was supposed to be a good used one in the recent past....relatively.

I pulled the cap and filter off, revved the motor to around 2500rpm, held my finger over the VTV, and the engine slowly returned to idle. What does this mean? Is it good or not? Shouldn't the motor stay revved?

thook

<<<<Bump!!>>>>

nate V

dash pot???? whats that and what is the VTV????

WFO

http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

Did you replace the dash pot? I was actualy just reading up on testing the TPS and saw this on the dash pot. It sounds like that could be the problem. If its not working or not adjusted properly it could be causing the RPMs to drop too fast.

If you slowly release the throttle and bring it back to idle does it still die?

thook

Here's the throttle body.http://personal.utulsa.edu/~nathan-b...93throttle.pdf
You can see the dashpot on the throttle linkage side. It dampens the throttle release. The VTV is the vacuum transmitting valve. It creates enough of an air "portal" that air can pass in and out of the dashpot and creating vacuum.

Thanks. I'm familiar with 4crawler's site and TPS adjustment.

I replaced the DP about a year ago suspecting it was a problem. It seemed to help at the time. I talked with a tech at the dealership and another mechanic about the dashpot and my results of testing it determined that the present one is good.

However, the tech at the dealership strongly believes it's the idle switch settings on the TPS. Couldn't be because I've set it enough times to know it's right on. The only thing I can figure is the soldering job I did on the wiring (at the time I replaced the dashpot) isn't making good connections. So, I'm going to test the TPS settings at the ECM and see if the signals are getting to it correctly. I've wondered about the splices before, but when I originally did it, it was working just fine. I don't remember if I had the wreck (a year ago) before or after I spliced them, though. Maybe they got screwed up in the wreck.????

Sometimes it's okay if I slowly release the throttle and sometimes not. An intermittent problem....sounds kinda of like an intermittent signal, doesn't it? Does to me. I'll find out, I suppose.

Thanks.

nate V

Thanks
Sounds to me like you are on the right track!
I think that you are on the right track with it being an intermittent signal problem. Im sure that you will figure it out. good luck

runslikecrap

hey my 95 3.0 auto 4runner does the same. Its new thing is to "cough" while im driving it, like everything f's up for a split second...idiot lights flash, power gone. Ive tried everything but replacing the tps cause shop tested it and said it was fine.

runslikecrap

"The idle/RPM seesaws and then it about falls flat on it's face and dies. It doesn't die everytime, but a lot.

If someone can help me figure this out and get it fixed, I may go ahead shoot the thing anyway just to relieve myself....."
X2!!!

thook

Thanks for the support guys. Very kind.

So far I've managed to get the throttle stop screw back to it's original location. I haven't gotten any further because it started dumping snow on us and had to pitch a makeshift tent over the vehicle. But, I will get back to it in a little bit and post what I find. In a way I hope this is the problem (with the soldering) because then I won't have to dig any further. On the other hand, it also means needing a new TPS wiring harness. Costly.....which is why I chose to solder it in the first place.

For those interested and for reference sake....if you should so happen to mess around with the throttle stop screw and don't how to get it back, the factory setting is .5mm between the stop screw and throttle lever. However, I've done it without the luxury of my feeler guages.....since I seemed to have misplaced them. Plus, I had the brilliant reference of where I marked the TPS setting when I originally adjusted. All you do is adjust the screw inward/outward...whichever direction it needs to go.....until it just touches the throttle lever. Then, just back it off very little until the throttle lever/screw on the TPS come to rest solely on the throttle opener. A delicate little balance, it is. If you wind up having to do this, you will have to also adjust the TPS accordingly as the throttle position/idle setting will have changed. Hopefully, you have feeler guages. Otherwise, it may take a couple of tries to get it right.

thook

Tested the TPS at the ECM and it checks out fine for both voltage and resistance. I then checked a bunch of other terminals at the ECM, but of particular interest is when I checked the VAM. I was testing for voltage and resistance throughout the procedure on everything and when I came to the VS terminal (at the ECM) for the VAM, I got a low voltage reading. Not by much, but the spec is supposed to be 2.3-2.8 volts between the VS and E2 (E21) terminals. I got 1.69 volts. Being that the spec range is so fine, I'm concerned, but I really don't know what it means. I will have to ask someone who has that knowledge.

For your interest, to those who would like to delve deeply into the realm of Techdom, I found these sites and pages while researching. Very, very informative. Info surpassing that of our beloved FSM. Speaking of which, the fellow/a friend of mine in the parts dept at the dealership (the one I've been speaking of.....and he's not the tech, btw) is going to let me borrow THEIR FSM. I was talking with him earlier this evening and we were swapping info. Their manual is a lot more detailed than the '93 FSM we have stickied here....and the one I, of course, have referred to since joining this forum.

Anyhow, here's the links to the sites I mention. I suggest fav'ing them if you plan on seriously figuring out how your vehicle works. The first site I've run across before, but the second was a golden find.

http://www.autoshop101.com/forms/h34.pdf

http://64.233.167.104/search?q=cache...lnk&cd=4&gl=us

Neither of these are the main page for either site, but certainly one could find it.

thook

Furthermore.....

The VS terminal at the ECM is the wiper track variable voltage terminal. It's connected to terminal #6 at the VAM....the wiper track signal. It signals the flap position to the ECM.

This is getting interesting....

Look at the autoshop link on page 5. It shows a diagram of the AFM/VAM. In the paragraph above that diagram it explains how the VS operates. Can't say for sure yet, but it's possible the voltage reading I get is only a reflection of a low/poor idle and not necessarily the cause.

There is a test at the ECM to run on the same terminals except the test is run while the engine is maintained at 3k rpm's. It will be interesting to see how the voltage reading changes accordingly.

Anyway, just sharing some thoughts. No conclusions, yet.

thook

It was the dashpot. More tomorrow. I'm.....

ddiablo

mabey this is my trucks problem, i thought it was only the injectors but it is'nt my truck nearly stalls when i let off the gas @ around 3000rpm, and other times its fine. at first I was like wtf, ive checked my manifold, and taken it apart, along with the fuel rails but there isnt any problem there. I dont paying attention to how fast i let off the gas, mabey its that or the dash-pot thing, my truck has gone many miles, everything is old and warn out besides the engine. some things just dont work hardly at all any more; stereo volume, the clutch(agravating), and seat adjuster (forward-backwards).

WFO

Nice find Thook.

Can we sticky these? I know I might need these in the near future.

thook

Maybe. Start a thread, if you need to. We can talk about there.

Definitely.

I don't see why not. I found them free via internet search.

This morning I started the truck and it ran just fine. Problem is completely gone... In fact, I even drove it to work. There's still a few minor glitches in the vehicle to figure out and fix, but I'm also rebuilding the motor in my '86 (hey, that rhymed... ), so I have to kinda juggle things as necessary.

But, now I'm sad. This thread was so short lived.......

thook

Oh, and just for curiosity.......I found out why exactly there is a dashpot. Not sure on 5spd equipped vehicles, but atleast on auto's it's there to compensate for extra vacuum load from the transmission so the motor isn't starved at throttle release. Then again, it may be just for the total amount of vacuum load period. There's so many vacuum lines on this thing....

TNRabbit

Dashpot also helps on the manual trannys as it keeps the engine rpm up so when you shift the revs match closer to the speed you'll be when you release the clutch...(helps prevent the "jump" you get when you let the clutch out & the engine is at idle)....

nate V

thook
quick question the dashpot is there to dampen the butterfly valve when letting off the throttle correct?
also is the dashpot always supposed to be in contact with the throttle valve??? regardless of the conditions?
thanks ahead of time

thook

The first part I can see.....that makes sense, but the second part doesn't. When you let the clutch out? What jump? A jump in idle?