Morgenster
05-13-2006, 05:24 AM
Hi,
I tried hijacking an old thread to get some answers, but that didn't prove useful. So I'm trying a new one.
I recently bought a 1991 520i with M50 engine which has 260k km on it.
It's the best car I've ever driven (not that I've driven many, but still).
It's fitted with an LPG aspiration system. Where I live that's a serious bonus considering that premium fuel will cost you about 1,4 euro/liter and LPG is at 0,4 euro/liter.
I noticed something a little bothersome though:
When starting the car cold, idle will go down from 1,2k RPM to about 800.
After warm-up idle drops to 600 or less and at that point I sometimes get slight hesitation when I rev up. Tapping the accelarator doesn't give a quick rev, but a slight slowdown. holding throttle for more than a second gives me a steady rev.
In warm idle there's some misfires, which disappear at higher revs. Spark plugs have just been replaced.
For what it's worth, my mechanic said that the AFM is relatively new and shouldn't give problems.
I started to suspect the Throttle Position Sensor. Bentley says the range in resistance should be from 1K to 4K ohms. I get 2K to 5,6K, but without apparent flat spots.
Now here's my theory:
With 2K resistance at idle could the TPS be fooling the ECM into thinking that throttle is slightly open therefore not opening the ICV wide enough, subsequently causing slight hesitation when opening her up? Could it also be the reason why I don't feel a difference in pull between half-open and wide open throttle?
The reason I ask is because I don't really know the tolerances on the TPS measurements and I don't feel like replacing a 60Euro potentiometer (that's just wrong for a simple pot sensor) if it's not malfunctioning.
ANY input would be wildly appreciated since none of the other forums I visited had anything to say on this.
PS: I've been lurking a little to see how things work around here and I'm excited to see so many e34 enthousiasts in one board!
I tried hijacking an old thread to get some answers, but that didn't prove useful. So I'm trying a new one.
I recently bought a 1991 520i with M50 engine which has 260k km on it.
It's the best car I've ever driven (not that I've driven many, but still).
It's fitted with an LPG aspiration system. Where I live that's a serious bonus considering that premium fuel will cost you about 1,4 euro/liter and LPG is at 0,4 euro/liter.
I noticed something a little bothersome though:
When starting the car cold, idle will go down from 1,2k RPM to about 800.
After warm-up idle drops to 600 or less and at that point I sometimes get slight hesitation when I rev up. Tapping the accelarator doesn't give a quick rev, but a slight slowdown. holding throttle for more than a second gives me a steady rev.
In warm idle there's some misfires, which disappear at higher revs. Spark plugs have just been replaced.
For what it's worth, my mechanic said that the AFM is relatively new and shouldn't give problems.
I started to suspect the Throttle Position Sensor. Bentley says the range in resistance should be from 1K to 4K ohms. I get 2K to 5,6K, but without apparent flat spots.
Now here's my theory:
With 2K resistance at idle could the TPS be fooling the ECM into thinking that throttle is slightly open therefore not opening the ICV wide enough, subsequently causing slight hesitation when opening her up? Could it also be the reason why I don't feel a difference in pull between half-open and wide open throttle?
The reason I ask is because I don't really know the tolerances on the TPS measurements and I don't feel like replacing a 60Euro potentiometer (that's just wrong for a simple pot sensor) if it's not malfunctioning.
ANY input would be wildly appreciated since none of the other forums I visited had anything to say on this.
PS: I've been lurking a little to see how things work around here and I'm excited to see so many e34 enthousiasts in one board!