Engine stalling

I'm finished with the engine rebuild and I'm braking in the engine but I have problems with the engine stalling every now and then.
It dosn't just stop it dies when I lift of the gas. Let's say I shift into 4th at around 3000rpm and depress the clutch and the revs fall down as usual...but istead if staying at the idle speed it goes all the way down to 0 and the engine stalls.
This happends both at high revs and low revs and not all the time.Just every now and then.
My thought is that it's a vacum leak, but I have looked everywhere and didn't manage to find one.
The weirdest thing is that it dosn't do it all the time.
Any indeas?

Looks like my post is in the wrong section....can I have some help please???

hmm do you have a bov... almost sounds like it could be leaking and stalling if you have one..

also it could also be that the idle control valve needs to be adjusted a bit, turn it up a bit and see if it still hapeens and we can go from there...

Yes I do have a bov, it was my first guess but I made the spring so hard that it dosn't open....just to test it.

Hmm what's the idle control valve?If I start turning it won't the idle speed increase?
I didn't have this problem when I had the idle speed at around 2000rpm. The rpms stil droped way low but came up again.

Can someone explain to me how the idle speed is controled? There is the unit on top of the radiator where you can decide how much air is going in, then there is that strange, never working, bi metall thing that has 2 electrical connectors and 2 vacum hoses and then there is this thing....don't know the name of it, that sits on the intake mani, it has vacum hoses coming to it and electrical connectors.
How do they all work and what is doing what?

I also switched the tp to a ca18det unit.When doing this I noticed a smal screw that controls how closed/opened the butterfly is. Why is this thing here?
Shouldn't the butterfly be completly closed at idle and all air comming to the engine should go through the idle speed control units?
And also, how important is it to set the TPS?It says in the manual that it should be placed exacly at the place where it turns on.....????
After playing with it I noticed that there is a spot where idle speed increases so I guess that's the place where it should sit?????

I'm confused

are you running the et or the det engine? if it's the et engine, the tps only detects between idle and non idle. you can adjust this by loosening the bolts on the tps and rotating it. you'll need a multimeter to see when the actual contact is made.

are you running the et or the det engine? if it's the et engine, the tps only detects between idle and non idle. you can adjust this by loosening the bolts on the tps and rotating it. you'll need a multimeter to see when the actual contact is made.

I'm running the DET block and ET head. Could a missplaced TPS cause my problems?
In the FSM they say something about how to measure the TPS resistance but it dosn't say that it's the way to set it correctly. Just says how to test if it works....ow well...I'll but my multimeter there and see what happends.

well, first of all, congrats on getting your frankenstein motor together!

i guess it could be the tps, but i doubt it.

to check the tps: when you throttle is closed, you should have conductivity between the two pins on the tps (like 1/2 ohm). there are 3 pins on the tps but check the connector to see which of the 2 pins to test. when you open the throttle slightly, there should be no conductivity. on the connector, test the two sockets for conductivity.

i just found my harness is broken so my ecu never thinks it sees idle at all (no conductivity). but the car still runs and doesn't stall. yes, i'll be fixing this soon.

I'm running the DET block and ET head. Could a missplaced TPS cause my problems?
In the FSM they say something about how to measure the TPS resistance but it dosn't say that it's the way to set it correctly. Just says how to test if it works....ow well...I'll but my multimeter there and see what happends.

Thanks Sshung but it's far from a Frankenstein....thinking....hmm the monster was ugly and loud....hey...IT'S ALIVE.
Anyway you where right, the tps dosn't change anything. I got pissed on my car so I started pulling out connectors, water temp sensor, IAA unit and to the bimetal thingy. It dosn't affect the car too much.Almost nothing. The rpm dosn't move.Shouldn't something more drastic happend?

No more ideas?

what about timing? is there a difference between the det and et crank sprockets? you can affect your idle by messing with the distributor a few degrees (at least on mine you can!).

Yes the DET sprocket is diffrent from the ET. But the ET sprocket dosn't fit the DET crank shaft so I used the ET crank to get the timing correct.

It seems that the stalling thing happens more often when the engine is hot????

if it's when hot it could be a lot of things. temp sensor, bi-metal air valve thing, etc. but if you didn't have this problem before, i don't know why it would suddenly appear. is your temp gauge showing you running hotter than before? is your oil pressure dropping more than it was before?

if it's when hot it could be a lot of things. temp sensor, bi-metal air valve thing, etc. but if you didn't have this problem before, i don't know why it would suddenly appear. is your temp gauge showing you running hotter than before? is your oil pressure dropping more than it was before?

How could I test the temp sensor? I am guessing that the bi metal valve is broken...since it's ALWAY broken on our cars, how much does that affect?
My temp gauge is normal, I have a new thermostat so everything looks normal. The oil pressure seems a little low, normal but low, but I was just guessing it was the sender.

Just a theoretical question. What if the MAF was placed verry close to the turbo, could the turbulance from the turbo somehow disturb the MAF? The car runs fine at hight throttle.