Dear Scotty,
great channel without sponsors and great advices. There is an issue on my BMW 316i model E30 from 1990, engine M40B16, capacity 1.6L, 102ps, model with a catalyst. The car has some above 300000 km and is completely restored in 2017 by original parts. At about 5 to 10 seconds after the start the engine begins to stutter, it does not respond well to the throttle and it lasts for about 30 seconds to about a minute, then it suddently stabilize and works correct in either idle or drive. First my mechanic BMW certified suggested to replace the air mass flow meter, but nothing changed. Then the BMW support suggested to change injectors, but it had no effect. Then we changed temperature sensors, it has no effect. Then we measured the fuel pressure it is 3.0 bars at start and when it suudently stabilize it is 2.86 bars. As to the manual 3.0 bar is standard for this car. If the idle valve is disconnected from supply there is a little more shake at start but generaly the same, it has initial stutter, after half a minute it stabilize then it works fine. The test with a BMW service computer did not show any issue. It is only appearent now at the winter cold, at 2 C degrees, that it starts ok, but after it is heated after or at the summer temperatures, it results in stutter.
There are no more ideas what to do, could you please help?
Thank you and best regards,
Robert
Could be the intake manifold gasket. When the engine heats up the parts expand and the intake manifold leak closes.
Next time it does that, pop the hood and spray some carb cleaner or brake cleaner around the base of the intake manifold where it mates to the cylinder head and see if the idle smoothes out some.
gaskets of the intake manifold are all set new and original. The only other thing to note, if petrol engine system cleaner liqyu molly professional is added to the fuel, on that tank there is no issue. The next fuel tank is loaded, the issue comes again. The car was initialy without catalyst. The problem got stronger this year when it was installed.