3-Series (E21, E30)Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.
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It seems like after a long drive if I stop and go into a store and then restart it the engine struggles to stay running. It starts no problems but goes "vroom" (then rpm goes down like engine cuts off from gas) then "vroom" and repeats that until it shuts off. And if I apply the gas sometimes it will rev up and sometimes it sounds like it will shut off. After a few minutes of reving and restarting it idles fine and drives like nothing was ever wrong! I did just replace the fuel pump but i dont see how that could be the problem. Can someone try and help me narrow it down to what the problem is?????
.... MAF doesn't appy to your car... you have a AFM (Air Flow Meter...)
Hows your MPG?
HowsDoes the car feel when it is warmed up?
It could be Leaky injectors Cold start injector or the tempature Sensor...
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after it goes through the erratic idle for a few minutes or so, it idles and runs like nothing ever happened. I took off the intake housing and cleaned off the Air Flow Sensor even though it looked clean. while it was off (both air filter and Air Flow Sensor) i started my car and it ran exactly the same as it would with the filter and sensor plugged in. so im thinking it could be the sensor.
And i wouldn't even know how to check the injectors, cold start injector, or the temperature sensor to see if they are fine
Since this happens after a long drive (hot), I might suggest that you may be experiencing vapor lock in the fuel lines... especially if you just replaced the fuel pump... the new pump may have a bad check valve allowing the fuel pressure that should be built up in the injector rail to bleed back to the tank. If that happens and it is hot under the hood you will have a pressurized gas inside the fuel lines and it will be difficult for the liquid gasoline to get back up to the injectors. Has it been a little long cranking when it's cold as well? If so, next time you go to start it cold, turn the ignition on and of about 3 or 4 times and see if it starts up real quick that time. That will run the fuel pump prime sequence several times and re pressurize the fuel system that had previously bled off, if that is the cause. The other issue could be the fuel pressure regulator. You can test it fairly easily by pulling the vacuum line on and off of it while its idleing. You must put your finger over the vacuum line immediately upon removing it or it will cause the motor to stumble. If removing the vacuum from the FPR has no effect on the engine, you could use a new one.
.... MAF doesn't appy to your car... you have a AFM (Air Flow Meter...)
Hows your MPG?
HowsDoes the car feel when it is warmed up?
It could be Leaky injectors Cold start injector or the tempature Sensor...
Before I replaced the fuel pump my OBC was saying 33 mpg and now it's reading 29 mpg. any idea why? and cleaning the AFM seemed to help a little and it has been running better (only idled weird one time). gas mileage has me puzzled though.
Since this happens after a long drive (hot), I might suggest that you may be experiencing vapor lock in the fuel lines... especially if you just replaced the fuel pump... the new pump may have a bad check valve allowing the fuel pressure that should be built up in the injector rail to bleed back to the tank. If that happens and it is hot under the hood you will have a pressurized gas inside the fuel lines and it will be difficult for the liquid gasoline to get back up to the injectors. Has it been a little long cranking when it's cold as well? If so, next time you go to start it cold, turn the ignition on and of about 3 or 4 times and see if it starts up real quick that time. That will run the fuel pump prime sequence several times and re pressurize the fuel system that had previously bled off, if that is the cause. The other issue could be the fuel pressure regulator. You can test it fairly easily by pulling the vacuum line on and off of it while its idleing. You must put your finger over the vacuum line immediately upon removing it or it will cause the motor to stumble. If removing the vacuum from the FPR has no effect on the engine, you could use a new one.
Good luck... I hope the IAC valve was the issue.
Ill try checking the FPR as soon as I can and I'll let you know how that turns out. Thanks for all the help guys! hopefully it just badly needs a tune-up!
i never check the FPR but it has been running good ever since i took off my throttle body and cleaned it all out. HOWEVER, my gas mileage went from 33+ mpg to 27.6 mpg! so i dont quite know why this happened...
It seems like after a long drive if I stop and go into a store and then restart it the engine struggles to stay running. It starts no problems but goes "vroom" (then rpm goes down like engine cuts off from gas) then "vroom" and repeats that until it shuts off. And if I apply the gas sometimes it will rev up and sometimes it sounds like it will shut off. After a few minutes of reving and restarting it idles fine and drives like nothing was ever wrong! I did just replace the fuel pump but i dont see how that could be the problem. Can someone try and help me narrow it down to what the problem is?????
When i took off the throttle body, there seemed to be a vacuum hose going into it after the valve. The hose on the outside was loose so i zip-tied it tight. maybe that was just the problem?
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1988 325is idle issues! HELP! 
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