infamous 5MT low idle stall

[TomsSVX]

Dan, the clutch release is adjustable. I set it there and since there was full engagement did not move it. If you would like it moved out I can show you how to do it

Tom

[shotgunslade]

Tom:

Thanks. I'm just getting used to it. It's been 8 years and 2 SVX's (this one is now so different it has to count as a 3rd) since I drove stick as a daily driver. Sheila and I were talking today about my previous cars, and all before the SVX's had been manual. Two VW Beetles, a Chevy El Camino, a BMW 2002tii, a Fiat Spider, an Alfa Romeo Berlina, a Honda Prelude, and a Porsche 911, but 8 years is pretty long. Upshifting is not a problem, nor downshifting into anything but first. They go smoothly without consciously making sure the clutch pedal is on the floor. Maybe I'll make a list of adjustments and some further minor mods, and take a trip down to Beach Haven in a little while and buy some of your time. If you guys work out a dashpot thing, I'll definitely be buying one of those.

Mohrds:

I bought a complete Sti pedal assembly on eBay, and Tom rebuilt it and used it as a complete replacement for the SVX pedal assembly.

[TomsSVX]

Dan, sounds like a good idea. I never downshifted into 1st in any of my vehicles. I wait until I am stopped to put it into 1st. The synchos are always tight and I feel like I am going to break something when I do it. Thats not the clutch pedal but more the transmission holding it back.

Tom

[oab_au]

Originally Posted by mbtoloczko

It did occur to me yesterday that there is one instance where the dashpot may not prevent the stall. I have found that sometimes during a long decel with the tranny in gear and coming up to a stop sign (say taking a freeway offramp), as I come up to the stop sign and put the car in neutral, the engine will stall. A dashpot will have allowed the throttle body to have closed long before I reach the stop sign, so it seems to me that the dashpot may not help here.

With my car, I don't think the stall has to do with the tranny having a pull clutch. There is no change in idle speed with the clutch engaged or disengaged. Turning the steering wheel when coming up to a stop will exacerbate the stall though. The extra load placed on the engine by the PS makes it more difficult for the engine to recover from a very low idle. I've cleaned the throttle body and IAC very thoroughly and all the vacuum lines are brand new, so I think the lightweight flywheels definitely contribute to the stalling.

There does seem to be a couple of things going on. The sudden closing of the throttle, can be over come with the dash pot.

The stalling when running to the stop, with a closed throttle, is more a ECU problem. First the ECU has been told that the trans is in N, so it has been trying to control the idle speed, that it should be able to in this condition. But the engine is not free to control. The engine speed is being controlled by the drive train.

When running into a corner with a closed throttle, the ECU is trying to slow the idle down. So it winds the Idle Control unit down, but the engine does not respond, so it winds it down further. Then you get to the stop, push the clutch in, all of a sudden now, the engine can responded but, because the Idle Control unit has wound the control right down, the engine stalls.

To fix it you may have to try different positions of the ECU N, P, D, shift inputs to cure the problem.

Harvey.

[mbtoloczko]

Originally Posted by oab_au

...

When running into a corner with a closed throttle, the ECU is trying to slow the idle down. So it winds the Idle Control unit down, but the engine does not respond, so it winds it down further. Then you get to the stop, push the clutch in, all of a sudden now, the engine can responded but, because the Idle Control unit has wound the control right down, the engine stalls.

To fix it you may have to try different positions of the ECU N, P, D, shift inputs to cure the problem.

Harvey.

This is pretty much what I feel is happening with the light flywheel exacerbating the problem. I've got the ECU pinouts jumpered to make the ECU think the non-existent 4eat is in neutral. When I had it set to think the 4eat was in drive, the problem was worse. I'm thinking that a dashpot is an inexpensive solution that would help in some instances, but if there was a way to modify the IAC algorithm, that would be the ideal solution.

[oab_au]

Originally Posted by mbtoloczko

This is pretty much what I feel is happening with the light flywheel exacerbating the problem. I've got the ECU pinouts jumpered to make the ECU think the non-existent 4eat is in neutral. When I had it set to think the 4eat was in drive, the problem was worse. I'm thinking that a dashpot is an inexpensive solution that would help in some instances, but if there was a way to modify the IAC algorithm, that would be the ideal solution.

I was think more of the P being used, with the clutch switching it over to N when it is pushed. So that the ECU won't be trying to control the idle speed, on a closed throttle overrun, till the clutch is pushed.

Harvey.

[oab_au]

What I meant was that the N, P, inputs to the ECU be left open, so the ECU knows that the trans is in gear. The N be switched on, when the clutch is pushed or the box is in Neutral.
This would stop the Ecu from trying to stabilize the idle speed when it is coming to a stop.

Harvey.

[huck369]

Originally Posted by oab_au

What I meant was that the D, P, inputs to the ECU be left open, so the ECU knows that the trans is in gear. The N be switched on, when the clutch is pushed or the box is in Neutral.
This would stop the Ecu from trying to stabilize the idle speed when it is coming to a stop.

Harvey.

But that would keep the cruise control from working....

[TomsSVX]

you don't want the cruise to when the car is in N anyway. This still will not cure the stalling problem though. The neutral switch in Shotgunslade's pedal assembly was not working properly so I had to hardwire it in Neutral all the time so he could start it. It still stalls.

Tom

[Earthworm]

Do you have any problems shifting into 2nd gear from a stop?
If so either the return spring in the clutch master is sticking or you can adjust the rod on the clutch pedal. I've had both issues.

[TomsSVX]

the rod needs to be adjusted but it does allow for full release


Tom

[shotgunslade]

Observed this tonite on my drive home from the train station. Approaching a right hand turn, I'm in second gear, braking, about 2000-2200 rpm. Push down the clutch pedal, and turn. The rev's drop like a stone. Suprising how fast. Revs seem to hit zero, all warning lights light up, but then, without letting out the clutch, engine sort of restarts on its own, jumps up to 800 rpm, and settles at 600 or so. What caught my attention was the rate at which the revs dropped.

Contrast that with the next turn. Same thing, except, momentarily, I take my foot off the brake and lightly, very very briefly touch the accelerator, just as I push the clutch down. Rev's rise only as 100 rpm or so, but the rate of rev drop when my foot is completely off the pedal is much slower, and it hits 600 rpm and stays there briefly, until I let out the clutch and give it some gas as I straighten out .

Seems like the ECU is actively trying to kill the revs in the first instance, overshoots, and just catches it before it has a chance to die completely. Touching the accelerator in the second instance stopping that from happening. So, I bet, this wouldn't happen if the throttle butterfly didn't immediately close completely when you take your foot off the accelerator.

No problems shifting into second while I'm stopped, as long as the clutch pedal is depressed.

[oab_au]

Originally Posted by TomsSVX

This still will not cure the stalling problem though. The neutral switch in Shotgunslade's pedal assembly was not working properly so I had to hardwire it in Neutral all the time so he could start it. It still stalls.

Tom

Yes Tom that is what I have been saying.

Look at it, the way the Ecu does. The Ecu has been told that the trans is in N, so it waits for the 'closed throttle signal', when this arrives, it starts to control the idle speed. It does this by reading the RPM, if it is high it will tell the Idle Air Control to close a bit, it then reads the RPM to see if it is low enough, if not it will repeat the cycle till the RPM is OK.


Now look at what is happening. You have closed the throttle and are coming down in speed to stop. The Ecu now has to maintain the idle speed.

It should not have to do any thing, as the idle speed was right, last time the throttle was closed.

The Ecu reads the RPM, it's like 1700, the Ecu tells the IAC to close down, it keeps looking at the RPM, expecting it to fall. But because the engine is still being driven by the trans, it can't slow down.

Eventually you stop. The IAC has been closed right down, you push the clutch in, the engine is no longer driven, it will stall, unless the IAC can act fast enough, to pick the speed up.

This condition can be made worse if the IAC is sticky and can't respond fast enough. But the other condition of suddenly closing the throttle to stall, needs the dash pot.

I think Huck has the N on the clutch, so the Ecu won't be trying to set the idle speed, till he pushes the clutch in. It may work better if the N was switched by both, the clutch, and the N position on the gear box.

Harvey.

[oab_au]

Originally Posted by shotgunslade

Observed this tonite on my drive home from the train station. Approaching a right hand turn, I'm in second gear, braking, about 2000-2200 rpm. Push down the clutch pedal, and turn. The rev's drop like a stone. Suprising how fast. Revs seem to hit zero, all warning lights light up, but then, without letting out the clutch, engine sort of restarts on its own, jumps up to 800 rpm, and settles at 600 or so. What caught my attention was the rate at which the revs dropped.

Contrast that with the next turn. Same thing, except, momentarily, I take my foot off the brake and lightly, very very briefly touch the accelerator, just as I push the clutch down. Rev's rise only as 100 rpm or so, but the rate of rev drop when my foot is completely off the pedal is much slower, and it hits 600 rpm and stays there briefly, until I let out the clutch and give it some gas as I straighten out .

Seems like the ECU is actively trying to kill the revs in the first instance, overshoots, and just catches it before it has a chance to die completely. Touching the accelerator in the second instance stopping that from happening. So, I bet, this wouldn't happen if the throttle butterfly didn't immediately close completely when you take your foot off the accelerator.

No problems shifting into second while I'm stopped, as long as the clutch pedal is depressed.

You posted while I was writing. Amazing is this what I have been saying. The dash pot will do it on the fast slow down, but a long run down to a corner will still cause the IAC to close down. Bliping the throttle, turns the closed throttle signal off, so it does not have to set idle.
Harvey

[rmjjensen]

Just something to kill all of your theories:

I do not have ANYTHING connected to my clutch pedal. Both switches are unplugged.

The ECU always thinks it's in Drive by me NOT grounding the P pin or the N pin coming from the Transmission harness. To start the car, the NSS on the transmission harness is jumped with a heavy gauge wire. Starting the car is not controlled by the ECU one bit, the NSS that was in the automatic transmission is what controls when the engine can start. Yes I don't have cruise control - and I don't care. Frankly the SVX cruise control is jerky the way it works - seems more like it doesn't smoothly control the throttle (maybe mine's broken but it's not necessary when I drive anyway).

With that said, my car is always in drive, regardless of what gear the 5MT is in or whether the clutch pedal is pushed in or out.

I have the 5MT idle stall once in a blue moon. It rarely happens but I can MAKE it happen. Generally when you are turning the wheel and suddenly push the clutch in it sometimes may stall. I believe this to be the power steering pump sucking the little juice that the IAC is feeding into the engine.

Want a fix? send +10V to the AC activation wire of the ECU. This will raise the idle to about 750rpms. At the same time, interrupt the output from the ECU that feeds the AC Compressor so it's not always on with a 9V relay. Take the wire coming from the HVAC that used to feed the ECU +10V when the AC Compressor is to kick on and feed it to the relay to activate the compressor when it's really needed and complete the connection you just interrupted. Only draw back is the dam cooling fans ...it can cause both to go on because it thinks the AC is going. I'd have to build a temp sensor circuit to control the fans externally - which wouldn't be hard at all - just lazy.

But it works - put your Defroster (or AC) on and unplug the trigger wire at the compressor temporarily - see if you can make the SVX stall