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?

[Geezer914]

1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.

[tshih914]

1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.

I assure all that the AFM is plugged in and my fuel pressure gauge reads 28psi. One other piece of info is when the engine is "idling" at 3000 rpm I placed my hand to cover the nozzle of the air box housing feeling for vacuum from the air passing through the air filter into the AFM and felt little air flow! This means that there is an air leak (like when you adjust the idle by opening the screw at the base of the throttle to bypass the AFM). I had replaced the intake boot when the initial problems showed up. When searching for vacuum leaks there are lots of hoses and connections and even the O-ring gasket under the oil filler cap to check. Also is there an auxiliary air flow sensor in the 1974 1.8L FI system?

[wonkipop]

1+ on the AFM not being connected. Check for vacuum leaked. The intake boot may have a crack.

I assure all that the AFM is plugged in and my fuel pressure gauge reads 28psi. One other piece of info is when the engine is "idling" at 3000 rpm I placed my hand to cover the nozzle of the air box housing feeling for vacuum from the air passing through the air filter into the AFM and felt little air flow! This means that there is an air leak (like when you adjust the idle by opening the screw at the base of the throttle to bypass the AFM). I had replaced the intake boot when the initial problems showed up. When searching for vacuum leaks there are lots of hoses and connections and even the O-ring gasket under the oil filler cap to check. Also is there an auxiliary air flow sensor in the 1974 1.8L FI system?

there is no auxiliary air flow sensor in the L jet.
but there is a cold start aux air flow valve. AAV.
provides extra air to the engine during cold start.
but its connection is in the boot and after the AFM flap.
so it causes the AFM flap to deflect and for the car to receive extra air bypassing the closed throttle. there are two other sensors to measure temp. the main one at a cold start is the cylinder head temp sensor telling the ECU the engine is cold. i doubt the AAV will cause of the 3000 rpm high idle. it will raise the idle if its stuck open but not usually to that extent. not from stone cold anyway.

its a matter of downloading the manual and testing each component methodically 1 by 1.

i'm not sure exactly what is causing the engine to die when you gas it for revs.
apart from the AFM not communicating properly with the ECU.
i've got some other L jet diagnostic manuals. i'll look through them to see if thats a specific fault mentioned. as you mentioned - you had this fault initially before AFM explosion. so its something there you have not found yet despite the rebuilt AFM unit.

i don't want to speculate too far, but one of the components on the check list will the throttle position switch. i'd have to read further on what that might lead to if its faulty or not operating correctly.