I have an issue with my 740 where it randomly dies when shifting gears, accelerating from idle, and sometimes just upon startup. It starts fine every time, and once it gets going I don't usually have any problems. I have also gotten it to work by holding the throttle open under the hood while someone else cranks it over, but it still wants to die when shifting gears (automatic). Note that this doesn't happen every time I drive it, but enough where I can't reliably use the car. Right now I set the idle adjustment screw so that it idles really high, so it doesn't die as much at an intersection.
Things I know that are wrong:
- my ignition switch is worn, because it wants to stick in position where srs light is on and radio is off.
- i think I have a vacuum issue, because the heat/air system only blows through the top vents at low rpm, and when my turbo gauge goes up, it switches to floor/defroster vents by itself.
- pcv breather hose is in bad shape, not sure if that would effect this issue
I've seen in other forum posts that my issue might be from vacuum leaks, but I don't know how to check for that. I replaced the most obvious vacuum lines under the hood with silicon vacuum lines many months ago, and i'm 99% sure I did it correctly, plus this problem only arose recently. also saw someone saying maf issue, but my maf is only a year old (its oem and everything)
Other posts also say to clean the throttle bottle and IAC.
The reason why I'm asking for opinions before trying much is because I don't have easy access to tools and a place to work on it right now, so I want to try diagnosis before I start replacing things.
I'd appreciate any help and advice.
Thanks.

 

It will take some time to pinpoint your issue, don't replace everything all at once.
Start with vacuum hoses and check valves if you think that is the problem.
I don't have specific advice about your problem, just general troubleshooting advice.
Reply with updates

 

what do you mean by check valves?
i fixed a few messed up hoses, cleaned the throttle body, crankshaft position sensor wire was intermittent so i replaced that, in line fuel pump connectors were jiggling loose too so i fixed that, but the problem persists! maf is very clean and i can't find any vacuum leaks with a propane tester,
someone suggested the fuel line pressure regulator could cause it to lose power from lack of fuel, is that a "check valve"?
thanks

 

hello, the check valves are inline in some of the vacuum lines and may fail or get stuck. They look like this
https://www.fcpeuro.com/products/vol...xoC8AYQAvD_BwE
There is also a vacuum routing diagram posted on the inner fender/shock tower that may help you with engine bay vacuum line routing.
I don't know if cabin vacuum lines will cause your problem, but you can see most of them from the driver's side footwell