Car stalling AGAIN, Updates- none of them good. Options

[rjames]

Drove around for 30 minutes in 80+ degree weather. All arterial roads, so several stop lights, etc. No problems until I was almost home. Car stalled when I stopped at a light. RPMs just dropped to zero. Was able to start it again with a little difficulty and had to keep my foot on the gas to keep it from stalling out again. Power seemed ok though the rest of the way home (I think). It stalled once again at a stop light a couple of blocks from home and then again when I pulled in the driveway. I let it sit for 30 seconds, started it again and it idled just fine. Rock solid at 1000 RPMs. Pulled it into the garage where it sits now.

Prior to today the car has been running and idling perfectly since I went through the FI parts last year, which included installing a 123 distributor, new CHT sensor, a newly rebuilt mps (calibrated for correct afr on my engine), new vacuum hoses, NOS throttle body, rebuilt injectors, new fuel pump, valve adjustment and timing.

I haven’t checked the AFR since last year, not sure why it would change though.
It’s a ‘75 so the fuel pump is in the front, so I can rule out vapor lock I think.

Anyone have ideas as to why it would be stalling?

[yellowporky]

Did you ever replace the board on your TPS? 914 rubber sells them

[rjames]

Did you ever replace the board on your TPS? 914 rubber sells them

No, and not discounting it, but I'm stuck on how it would explain the engine stalling since the car will still run with the TPS unplugged. I did clean the board last summer even though the contacts looked good. It's been calibrated.

[Highland]

Did you ever replace the board on your TPS? 914 rubber sells them

No, and not discounting it, but I'm stuck on how it would explain the engine stalling since the car will still run with the TPS unplugged. I did clean the board last summer even though the contacts looked good. It's been calibrated.

Another WAG, but if your TPS is worn and intermittently telling the ECU you're at idle, I can see how you can go way rich or lean sporadically (depending on ecu and MPS settings) especially as engine compartment temps change.

Do you have a variable resistor between the cht and ecu? I find that adds an extra knob to dial everything in.

[rjames]

Did you ever replace the board on your TPS? 914 rubber sells them

No, and not discounting it, but I'm stuck on how it would explain the engine stalling since the car will still run with the TPS unplugged. I did clean the board last summer even though the contacts looked good. It's been calibrated.

Another WAG, but if your TPS is worn and intermittently telling the ECU you're at idle, I can see how you can go way rich or lean sporadically (depending on ecu and MPS settings) especially as engine compartment temps change.

Do you have a variable resistor between the cht and ecu? I find that adds an extra knob to dial everything in.

I like WAGs.
The premise makes sense to a point, but then doesn't explain why when the idle surge is happening, the rpms continue to surge when I open the throttle a bit and hold it in that position. In that condition the TPS wouldn't be reporting an idle state to the ECU.

I don't have a resistor between the CHT and ECU. Car ran great for 7+ years without one before this issue cropped up, so I haven't felt a need to put one in. I've also got 3 CHTs that I've tried, both used and new ones. All test in spec when measuring resistance cold and warm.