Manual gearbox Stall.

[Dessertrunner]

Okay so for as many years as I can remember we have all been trying to stop the car that have been converted to manul from stalling. Over the years many things have been tried and none seem to work.
What we do know,
- Mike says that there is no fuel map in the ECU under 700rpm so the engine shuts down if revs drop below that.
- Any adjustment of the idle control valve is corrected by the ECU learning ability.
- A million thinks have been tried and as yet I don't know of anything that works.

Here is what I think is the cause,
If you have a look at the idle control valve you will notice that the little baffel can fully close off the air to the engine.
During some of my trial a coupel of years back I noticed that when you lift off the fuel the valve fully closes to pull the engine revs back quickly.
I think that during this fully closed period the engine is staved for air so the revs drop to low (below 700).
Engine shuts down as a result.

My suggested fix is to drill a small hole through the body of the valve so as to bypass some air at all time. In this way even when the valve is fully closed the engine will be getting air flow to keep it running.
I have cut open a valve to investigate how best to do this. I will post images of it later and also when I get a chance I will install a modisified valve and report back.
Tony

[NikFu S.]

My engine does not always shut down below 700. Mine drops all the way down to the bottom, dash flickers a bit, but stumbles back to life without throttle input on many, many occasions.

I have noticed what you have described, mostly during geared deceleration. Someone said they found idle fuel delivery is maintained up to 1250rpm. I tested this for weeks and for hundreds of miles.

When I decelerate, if I return to neutral over 1250rpms the stall situation probability is greatly increased, but at or below 1250 the rpms drop smoothly to idle.

My thinking was the fuel delivery simply was not able to anticipate a sudden drop in rpm.

I dunno, though, I'm no expert. I only excel at noticing patterns. Am interested to see the results of your experiment.

[Wikedjuggalo]

No to sound like a jerk but, I have never had any of these problems. The closest I come is the fall to about 500 rpm and then back up like Nikfu described. I never have had it stall unless it was my fault (1st gear). The manual from what I remember stats the ideal speed to be 610+/- 100.

[Dessertrunner]

The rpm Mike mentioned could be lower I can't remember.
Tony

[icingdeath88]

I have a great many thoughts on the subject, which I will share with you after I get some sleep. :/

[icingdeath88]

Ok, I have been having the exact same issue since I installed the swap. I switched to a 94 ECU, which seemed to help at first, but doesn't (I have a '92 engine and should be using the 92 ECU).

~700 RPM seems about right. If it dips under that, sometimes, randomly it will stall and die.

It happens a lot more often when clutching in from engine braking, and close calls happen a lot more often too. What NikFu said also very much sounds like my blue car.

Mine is probably a bit more sensitive due to the cams, but I'm not quite sure, since it will idle for hours and hours if you let it. Most of the time when I clutch in, I give the gas pedal a slight tap to prevent it from stalling. If I do that, it never stalls, regardless of how high the RPMs are when I do it. Falls perfectly down to idle speed and stays there.

I have thought of two ways of fixing this. Raise the target idle RPM speed in the software until it stops doing that. Basically have to get one of the ROM writer things that Mike uses and play with it until it's right. That would probably also help with driveability, since you could let the clutch out a bit more before giving it gas when starting off.

I was thinking instead to trick the ECU into always using the target idle RPM from when it's in A/C mode, since that's a bit higher. There's several pins on the ECU pinout that are related to the A/C - one must do that. I have been planning to try this for a while now, but I haven't had the time. My blue car has no A/C so I haven't been able to check whether it still does the same thing with the A/C on.

It does definitely seem to be more fuel related than air related. I'm not sure that bypassing the IACV alone would fix that.

Also, why not instead just run a small vac line from the plenum to the intake behind the MAF? You could put a valve along it to adjust how much air flows through it.

[Tim]

I've had this issue occur when taking a turn with the clutch depressed and turning the wheel. Turning the wheel will generally lower the rpm and I have stalled. Since then I've generally always made sure i was turning while in gear and haven't encountered the problem.