Nowanker

If you're sure there is no external source, and the throttle plate is truly closed to spec (Butterfly sticks in the bore, + half turn on the limit screw is what I use in lieu of any 'real' spec)....
Extra air is coming from somewhere.
Maybe time to visit a pro.

Last Lemming

Unfortunately, there are no pros around here for this car, this forum are where my pros are at.

So I did some more research tonight, please let me know your thoughts on each item if you have something to say:

1. I started the car and immediately clamped off the vacuum line at the manifold that comes from the ISV, in the car just about died. Once the car was warmed up, however, it just dropped RPM - but did not die. My question is almost dying what you would expect if you clamped off the hose when the car is cold?

2. after I de-clamped off the ISV, I clamped off the hose coming from the Venturi into the manifold. The car just dropped RPM but did not die. The car was still cold at this point. Normal, not normal?

3. When I try jumping the B/C test port nothing changes in the RPM. What would that tell you?

4. Lastly, just a question, when the car is cold and you start it, the ISV should open up to allow more air to get the car to warm up and keep idle, correct?

5. I will try unplugging the ISV this weekend, if the wiring tests good I will pull the throttle body off and see if there’s some thing I missed that I can’t see while it’s on the car.

Nowanker

I'll ponder the above, and get back to you!

orig944

While you have it unplugged, briefly apply 12 V to the center terminal and ground terminal 1, the terminal that the black with red stripe wire is connected to. This will snap the ISV closed. Without reconnecting the ISV, start the car and let us know what happened.

Nowanker

Items 1 and 4:
The engine needs more air when cold, so it would be normal for the ICV to open more (stay open longer in it's cycle...) when the engine is cold.
If the ICV and circuit are OK, it would be logical that the system would be able to maintain cold idle speed more in spec, with the ICV working more in its normal range or toward the lower edge of it.
I'd expect the engine to still run on the air it's drawing in from elsewhere, just slower.
Seems like the ICV function is OK...
Item 2:
Sounds like that's a clue about the unmetered air... I don't think there should be any airflow there at idle.
I'd expect the ICV would pick up the change and maintain the idle at cold normal speed.
Maybe there's some damping or adaptability built into the system to keep a steady idle. Dunno... it has been about 20 years since I messed with a stock one!
Item 3:
See the last sentence, above!

With the engine warm, what happens when you clamp off both vacuum taps at the manifold?
The only air it should see would be through the throttle body itself. Might not even run...

I do have another suspect for an air leak... and it wouldn't show up with the smoke test.
If the brake booster is leaking, the one-way valve would prevent the smoke from flowing into it.
Test it with a vacuum pump.

Gage

There was mention of Vitesse earlier in the thread. Is this a MAF conversion or an engine management system?
Wondering about ignition timing and fueling parameters as they would also be able to affect idle speed.

Last Lemming

So, a couple of responses to above:

I blocked of the vacuum line going to the brake booster, and there was no change, so I suppose that means there is no vacuum leak there.

I do have the Vitesse system, and I have been in contact with John there, he and I tried working this out for a couple of weeks to no avail, but it doesn't appear to be his system that's causing this, at least not based on the monitoring program that comes with the Vitesse system.

Last night I was able to pull the plug on the ISV.

I tested the resistance from the center pin to pins on either side of the center pen and I got an OL, which means there shouldn't be a short between those wires unless I did the test wrong. But I also noticed that the wires going into the connector were cracked, but not broken, so I cut the old connector off and stripped the wires back and put on a new connector (I had bought one months earlier in case I needed to do this exact thing). But this didn't cure anything, the car still exhibits the same behavior.

Before I pull the TB off and go through that, there is one thing that is still nagging at me. When I jump the B/C pins on the test port there is no change at all in RPM and no amount of adjusting the TB screw has any effect on idle speed or quality. You might think that there is a vacuum leak then, but after changing all the hoses over and smoke testing the system from various points the only place some comes out is the air filter - which you would expect so I'm not inclined to think there is a vacuum leak. OH IF IT WERE THAT SIMPLE!!!

So my question is what if there is a short at the test port? Isn' jumping the B/C pins supposed to ground something and disable the ISV? if so what if something going on there could be the culprit? If so, how do I test this with multimeter, what am I looking for?

At some point, I'll need to pull the DME and check the connection there, but I just did this not too long ago and all the pins were solid, at least visually, I'll need to check the continuity between pin and ISV connector and Test Port (if possible).

I read somewhere on this forum (can't find it now) that there might be a fuse between DME and Test port but this is unconfirmed as far as I know.

T&T Racing

The electrical diagrams are available on the web for free.

Last Lemming

Yes I understand. If you look up above in my previous posts you see I post the electric diagram. But it doesn’t tell me what I should be looking for. I’m not an electrical expert, so while I can follow the wires, they don’t tell me what voltage I should see or anything else that I can tell. Maybe you more electrically inclined can, but I can’t. . That’s why I’m asking what test to do and what I should be looking for, if that makes sense.

orig944

I've given you two tests to do, that you have apparently not completed, in posts 27 and 34. I suggest you do the test in 34 first, to find out if your ISV can close and the idle RPM is lowered. If the ISV will close, then I suggest you do the test in post 27 to find out if it is the wiring, or your DME that has a problem.

Here is a video you should watch:


You will note early in the video his green test lead is connected to the black with red stripe wire. This, and the schematic, is how we now know that grounding pin 1 with power on pin 2 will close the ISV.

Last Lemming

I will be doing these tests this weekend. Thought I was going to do them last night but ended up spending my time on the making a new ISV connection. Sorry if I wasn't clear.

thanks for your input.

Chris_924s

Exactly what I was thinking is the ISV is either failing, or potentially the DME/ I'd have to go back in time before to see what the original issue was and revisit issue root cause. -- May be a combination of errors. I also never underestimate the potential of purchasing a NEW replacement part that has failures-- or the wires it connects to "cause broken".

I wish you patience- BTDT. Your horror story will have a good end if followed through to completion. I recommend 3 fingers of bourbon, a fine cigar and 2 days off. Then revisit.

Dan Martinic

?

In the old days, we called it a "choke"--the thing you pulled to limit air on cold engine and thus make mixture very rich.

Engine needs less air when cold

Since there is no easy way to accurately measure rpms, I set the idle so that no change when B&C are shorted (in other words, no change with ISV in or out as I presume ISV is keeping idle at appropriate level). Not sure why turning the bypass screw with B&C shorted has no effect. What happens if, while idling, you pull a vacuum line or even better the big hose post-AFM?

Nowanker

Engine needs more fuel when cold, to compensate for poor atomiation.
It also needs more air, to smooth the idle and compensate for increased friction.
Along with the old time choke, there was also the fast idle cam for that function.
Early fuel injection used a separate auxiliary air valve to supply the extra air, but now taken care of through the ICV.

Dan Martinic

Well well... seems it's been too long since I had carburation; thanks for the reminder... and for the explanation

Now I understand why our cars don't fast idle when cold. My wife's fuel-injected '05 Matrix still does though. Trying to imitate old carbs I guess?