1974 1.8L engine fast idle then stalls, Fuel injection issues Options

[tshih914]

My 1.8L 914-4 with stock Bosch L?-Jetronic FI after being stored several years started to develop a hard to start problem. When finally started would stall when I give the gas pedal any input to raise the revs. I suspect there was some kind of intake air leak and while fiddling around had a backfire which blew the AF meter which I had Pelicanparts repaired. After replacing the fuel lines with the stainless ones from Tangerine Racing and flushing out the fuel system with Techron the engine started to run normally for a short time. Now the engine can be started and fast idles at 3000 rpm but again any input to rev up the engine results in stalling. The idle adjustment screw at the base of the throttle housing is fully closed. Any suggestions on how to fix?

[wonkipop]

@Van B

thinking about his problem there are two tests he can do right now without fiddling with anything or altering things as they stand. given the engine starts and fast idles at 3000 rpm. its obviously getting fuel at crank and at idle. and plenty of air.

1. before starting check the operation of the throttle valve. move it around by hand and make sure it is moving freely and resting right back at closed position.

2. start it up and let it settle at its 3000 rpm.

3. clamp off the vac hose tightly shut between decel valve and intake plenum.
note what happens if anything. does idle change. (make sure you clamp the right hose, its the one that comes out of side of decel valve and goes to intake plenum EDIT - sorry it comes out of end of decel and goes to plenum - it operates the valve off vacuum, but thinking about it you can also clamp off the hose that comes off side as its getting the air from the intake boot, so either of those can be clamped off shut).

4. unclamp hose. let engine return to 3000 rpm if it did change.

5. clamp Aux Air Valve hose tightly shut between end of AAV and intake boot.
(clamp it before it gets to the Y junction into boot as you want to isolate the AAV. - the other hose off Y junction is going to the decel valve).
note what happens if anything. does idle change.

Refer excellent video by prof Van B of hoses posted above to know which hoses referred to.

report results of 3 and 5 back here.

------

[tshih914]

@Van B

thinking about his problem there are two tests he can do right now without fiddling with anything or altering things as they stand. given the engine starts and fast idles at 3000 rpm. its obviously getting fuel at crank and at idle. and plenty of air.

1. before starting check the operation of the throttle valve. move it around by hand and make sure it is moving freely and resting right back at closed position.

2. start it up and let it settle at its 3000 rpm.

3. clamp off the vac hose tightly shut between decel valve and intake plenum.
note what happens if anything. does idle change. (make sure you clamp the right hose, its the one that comes out of side of decel valve and goes to intake plenum EDIT - sorry it comes out of end of decel and goes to plenum - it operates the valve off vacuum, but thinking about it you can also clamp off the hose that comes off side as its getting the air from the intake boot, so either of those can be clamped off shut).

4. unclamp hose. let engine return to 3000 rpm if it did change.

5. clamp Aux Air Valve hose tightly shut between end of AAV and intake boot.
(clamp it before it gets to the Y junction into boot as you want to isolate the AAV. - the other hose off Y junction is going to the decel valve).
note what happens if anything. does idle change.

Refer excellent video by prof Van B of hoses posted above to know which hoses referred to.

report results of 3 and 5 back here.

------

@wonkipop

When I pinched off either one of the 2 hoses from the decel valve to the intake plenum the idle dropped from 3000 to closer to 1000 rpm. (result of 3)

The idle also dropped when AAV hose was clamped (result of 5.)