Engine stalls when releasing gas

[Jarnovdb]

First things first i drive a bmw e21 318i from 1981 now for 4months.

From the begining it had the issue that when the engine was cold the engine would start but idlle badly. I must always start the car 3 times and then it would stay on but when the engine was hot i could start it immediatly.

Now last week i was going to solve this problem and i did a bit of research and i came to the conclusion that it must be my warm up regulator so i took it out of the car and disassembled it.
And indeed the filter was dirty and in the reservoir of the WUR there was lots of oil so i cleaned it out and reassembled it, put it back onto the car and started it.
And the problem was solved the car started instantly and idlled verry wel, i even drove it for 15min whitout any problems.
But today i drove it and stopped for a red light and suddenly the engine stalls and now every time i stop or release the gas pedal to long the engine stalls.
Do you guys have any idea what the problem could be?

Hope i can fix it

[shadyracer01]

Im not familiar with 4 cyl engine set up but have a look at throttle bypass valve, if electric operated check it getting power, check for split air pipes and try cleaning with brake cleaner, if coolant heated type you can watch it move if you pour boiling water through coolant side of valve after cleaning. Another thing to check is the diode relay to see if power getting to cold start valve and time/temp switch which you need to test for power there as you crank the starter over. Check also Wur resistance (26ohms +/-) and if power there when its running.
Ive had similar issues resurrecting my 323i, the only part i havent touched yet is the WUR, but its running good but not perfect yet.
Theres a possibility that the barrel plunger inside your fuel distributor could be sticking if Kjet but id say check the above first.

Hope any of this helps, skol

[Jeroen]

Some additional info: the mechanical K-Jet fuel injection system has the two regulators working together:

Warm Up Regulator regulates the control pressure, ie the counter pressure on the fuel distributor plunger, and in that way it can make the mixture richer. This is being done by aforementioned bimetal strip (26 Ohn resistance and running on 12V) that operates a membrane inside the WUR and in this way regulates counter pressure. The membrane can get stuck and if you adjust your fuel mixture on the fuel dizzy in this condition, the engine will run lean when cold. You may have the WUR up and running again, but the fuel mixture may be way off now.

Aux Air Valve aka slider aka throttle bypass valve is either bimetal operated (electrical version) or by coolant temp (wax element mechanical version) allows more air flow through the intake thus 'asking' more air and in that way raising idle speed. These can also be defective or stuck of course with the same possible maladjustment issues as a result. However, apart from vacuum leaks I don't see many defects on this side, usually it is the WUR.

Temp Time Switch typically switches on for 8 seconds if the coolant temp is low. During these 8 seconds this operates the cold start valve, an extra fuel injector that is located centrally in the intake manifold to further richen the mixture. After these 8 seconds this switches off. If this section fails it will become slightly harder to start a cold engine (requiring longer cranking) but if the rest is set up fine it will start after a few secs. Once running for over 8 secs this section has no function or effect anymore.

My suggestion for now? Hook up an exhaust gas tester or a basic CO meter for starters, and check your mixture. For starters I'd try to set the warm CO to abt 1.5-1.8%.

[bealo]

Have you managed to sort this problem yet? I have the same issues but mine is not injection.

Wondered if you had any ideas?

[Jeroen]

Would be nice if we got some feedback indeed! But if your car has a carb, that's where you should look. Vacuum leak, maintenance backlog, needing a good clean and tune, the usual stuff. Perhaps Peter our carb specialist can give you some more specific hints based on your model.

[Mihajlo]

I had problems with carburated 315...

engine would run well only on WOT.
problem was clogged idle jet. I took it down and picked it with extremely thin wire and took out a cat hair.. (don't ask me how it ended up there)

and from then every time engine started to fool around on even opened throttle, I knew it was issue with jet.

Check main jet and idle one also!

cheers my friends!