Scott's 4.9 Formula

[TopNotch]

The VSS in the 4T60 on my 3800 works just like the crank position sensor on my 88 duke. It is a magnet inside a coil of wire, and it is positioned close to a metal wheel with slots in it. As the slots pass by the magnet, they disturb the field and generate electric pulses.
Assuming that the 4.9 originally had a 4T60, it's PCM will want to see the same kind of VSS pulses, and I'm sure they are different from what a Fiero-type VSS produces.

[Raydar]

It did the pull up to a stop sign and die thing with me

The only other option (other than the rather sketchy Dakota Digital adapter) is to pop the plug out of the throttle body, and set a "minimum" idle speed. It kind of over-rides the ECM and ISC.

Here's the long story, because I don't have anything better to do...
What happens is that, if you're coasting with your foot off the gas, in gear, the ECM is trying to slow down the engine to idle speed. (Remember... it sees NO meaningful speed input.)
It tells the ISC to reduce engine speed. Of course, since it's a manual, and you're coasting in gear, the engine does not slow down. The ECM finally closes the throttle completely, trying to get the engine to idle down.
When you finally push in the clutch, the engine stalls because the throttle is completely closed, at the behest of the ECM/ISC. Hence my comment about setting a "minimum" throttle opening with the throttle body screw. 

...
Assuming that the 4.9 originally had a 4T60, it's PCM will want to see the same kind of VSS pulses, and I'm sure they are different from what a Fiero-type VSS produces.

Exactly right. Different in wave shape and frequency.
 

[Fierofool]

So, to prevent the stalling, would jazzing the throttle a little at the time of disengaging the clutch do the trick? 

[scottb]

It did the pull up to a stop sign and die thing with me

The only other option is to pop the plug out of the throttle body, and set a "minimum" idle speed. It kind of over-rides the ECM and ISC.

The plug has been removed (wasn't me, someone else got to it first). It's a bitch to adjust the throttle stop.

What I don't understand is why it drove for years without this issue...... now it comes up?

And this car has a bulb in the socket as I have seen the "Check Wallet" light

[Raydar]

So, to prevent the stalling, would jazzing the throttle a little at the time of disengaging the clutch do the trick?

Probably. But maybe not necessary. Look back at my edited comment. A "minimum" idle speed can be set.

[Raydar]

The plug has been removed (wasn't me, someone else got to it first). It's a bitch to adjust the throttle stop.

What I don't understand is why it drove for years without this issue...... now it comes up?

And this car has a bulb in the socket as I have seen the "Check Wallet" light

Ed, and company, probably tried to set the minimum idle speed/throttle opening. I would have.

The VSS thing is a well known issue. The stuff I quoted was posted elsewhere, like ten years ago.
Posted by people who were swapping V8s into S10s. But it's the same deal.

Otherwise, I can't explain anything that happened before you got the car. Take everything you were told with a grain of salt.
"Ran great, right up until it didn't." Right.
Anything else? Nothing would surprise me.
My Check Wallet light was NOT installed. Maybe they learned, by then.

[Fierofool]

Steve, Troubleshooter wants to know if the rotor on the 4.9 can be installed 180  out.  It mounts with 2 screws, not like the Fiero that has a keyed slot on the shaft. 

[Raydar]

Steve, Troubleshooter wants to know if the rotor on the 4.9 can be installed 180  out.  It mounts with 2 screws, not like the Fiero that has a keyed slot on the shaft.

I don't know. He should try it. I suspect not.
I think it has a "tit" on the end of the plate, where the rotor mounts, that fits a notch on the rotor. I don't think it will work.

[Wreck It Ralph]

Nope. It’s keyed on the sides. Well there is a tab. Or I’m remembering incorrectly. If it’s like most GM v8 distributors.

[Fierofool]

Scott says it's keyed, too. 

[Fierofool]

I had a chance to drive the car today. The idle changes from rough to smooth, depending upon what the oil pressure gauge is doing. When it pegs, it runs very roughly. When it drops down to a proper oil pressure, it runs smoothly. This is an intermittent thing of about every 10 seconds. I don't know which is the one creating the effect. The temp gauge will quickly move to the red, but it doesn't seem to be overheating.

Under acceleration, it seems as if the timing is off. Initially, it will lurch with good power, then it begins what I think sounds like a misfire. Whether that's caused by too much or too little advance will have to be determined by Troubleshooter. My damaged hearing range doesn't easily detect spark knock.

So, they are going to look at the old distributor to see if there's any alignment indicators and also look into the Field Service Manual engine rebuild section for information on resetting the distributor after a teardown.

Just found out the old distributor was tossed and isn't available any more.  Different approach. 

[Raydar]

I had a chance to drive the car today. The idle changes from rough to smooth, depending upon what the oil pressure gauge is doing. When it pegs, it runs very roughly. When it drops down to a proper oil pressure, it runs smoothly. This is an intermittent thing of about every 10 seconds. I don't know which is the one creating the effect. The temp gauge will quickly move to the red, but it doesn't seem to be overheating.
...

All that other stuff notwithstanding, this really sounds like a ground problem. The offscale gauges, especially. But if it also makes the car run poorly, it's not surprising.

[Fierofool]

That may be.  My 87 oil pressure is unplugged because it blows instrument panel fuses when plugged in.  When it's unplugged or removed from the sending tube, plugged in and the ignition on, it loses its ground and pegs. My thoughts are that it may have to do with the relays.  Scott said there was a pair of relays in parallel that I believe fed the fuel pump.   

[scottb]

No, the fuel pump and AC relays were moved from behind the air filter. There is an extra relay that is wired in to provide power for those 2 relays. To find why it's wired like that you will have to talk to the rocket surgeon in Huntsville cuz I have no idear.

[Raydar]

No, the fuel pump and AC relays were moved from behind the air filter. There is an extra relay that is wired in to provide power for those 2 relays. To find why it's wired like that you will have to talk to the rocket surgeon in Huntsville cuz I have no idea.

Seems like I remember that. Still can't explain why he did it that way, however. (From the department of redundancy department?)
BUT... normally the fuel pump is wired hot at the fuse box. A bad idea IMHO. The "upstream" relay may have been a way to "fix" that. Or not.
But that's not really applicable to the task at hand. Just a random thought...