Idle vibration + hard start

[Jordan325iC]

I had two issues, not sure if they're related.

The car takes a while to start. It always starts first try, but it has to crank for 5-10 seconds. It helps if I give it a few dabs of the throttle. When the motor is warm it starts right up.

Also, the engine vibrates the car very noticeably at idle. I just replaced the motor mounts with OEM units, so that's not the problem. The idle is a steady 700rpm, but the motor looks like it wants to shake out of the bay.

I've seen the coolant sensor mentioned in threads about both. Any ideas? Could the issues be related?

[BimmerBall]

i could be wrong but i think your starting issue is the fuel pump. apparently there's some drainback valve in it that takes a shit and lets all the fuel drain back into the tank. it' s a non-user servicable part so you have to replace the whole fucking fuel pump. therefore its hard to start cold b/c there's no fuel in the line and starts good when its hot b/c there still is. I'm having the same issue and am looking hard at a new fuel pump. Mine makes more noise than the exhaust. Oh, I replaced the coolant temp sensor as well and it didn't make a difference with respect to cranking times. YMMV

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[Jordan325iC]

What does the fuel pump sound like? I've had an rpm-dependent whine, sounds almost like a supercharger, since I've had the car. Is that the sound of a bad fuel pump?

Think that might help the the vibration problem too?

[jlevie]

Slow to crank could be a loss of residual fuel pressure (bad high pressure pump or bad FPR). It is easy enough to test for that condition by inserting a gauge in the fine that feeds the fuel rail. Low fuel pressure could cause a rough idle, but it would tend to affect higher rpm operation more. Since you don't mention any drivability problems I suspect the idle issue is something else. Likely candidates would include bad plugs, ignition wires, distributor rotor/cap, misadjusted valves, intake leaks, bad AFM, bad injectors, etc.

[BimmerBall]

yeah, i know its a little old.

dude, i found out what my problem ended up being. i've been so fucking furious about my shitty idle i decided, "fuck it, i don't care anymore" and went and took off the tps off the throttle body. then snapped the clips off and opened it up. christ on a pony it was full of dirt, grease, oil, and shit. so cleaned it up w/ brake cleaner and then some electrical contact cleaner and reinstalled. voila! starts so fast i can't let go of the key fast enough and it idles just as smooth at a nice even ~800 rpm. didn't want to leave you hanging and thought you might be interested in a possible solution....HTH



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[jlevie]

Oil in the TPS is a common problem. After the engine has some age on it oil will get into the intake from the crankcase vent or valve seals. Because the TPS is mounted underneath the throttle body any oil that seeps down the butterfly shaft will wind up in the TPS. Had BMW mounted the TPS on top of the throttle body that would not be a problem, but...

The fix for this is to drill a small hole in the TPS body in line with where the butterfly shaft enters the TPS. That allows any oil to drain out.

[Jordan325iC]

Thanks for the follow up! I will definitely check that this weekend.