After trying to find the cause of some uneven engine behaviour at constant speed, I unplugged the throttle position sensor to see if it would be better or worse. It was much smoother. (As you would expect transient reponse was worse as the TPS is feed forward, so hard accel is slower basicly)
So: Firstly I measured the resistance over pins 1 and 3 and it was 5.6Kohms (it should be 4k ohms), resistance across pins 1 and 2 varied between 0.8 and 6.4kohms. So even at this stage it was clearly not working right.
Then I hooked it up to a data logger at work and could see that although the max voltage was ~5V and minimum was ~1V there was a big step in the middle of the range. Jumps from about 20% to 40%.
So when driving along at constant speed it was stepping telling the ecu that the throttle was much more open than it really was.
Moral of this story is when a garage says your throttle position sensor 'is fine', unless they have a plot of voltage v's position they have no idea if it fooked. Some garages will open to throttle slowly and look at the voltage - two well respected indys (probably the two most popular on this forum) did this and failed to spot the problem.
New sensor is £51.67 +Vat from BMW, I'm picking my new one up tonight.
Also just to note it is safe to drive without the TPS for diagnostic purposes as the MAF and Lambda sensors will keep the fuel mixture safe.
Cheers,
Craig
So: Firstly I measured the resistance over pins 1 and 3 and it was 5.6Kohms (it should be 4k ohms), resistance across pins 1 and 2 varied between 0.8 and 6.4kohms. So even at this stage it was clearly not working right.
Then I hooked it up to a data logger at work and could see that although the max voltage was ~5V and minimum was ~1V there was a big step in the middle of the range. Jumps from about 20% to 40%.
So when driving along at constant speed it was stepping telling the ecu that the throttle was much more open than it really was.
Moral of this story is when a garage says your throttle position sensor 'is fine', unless they have a plot of voltage v's position they have no idea if it fooked. Some garages will open to throttle slowly and look at the voltage - two well respected indys (probably the two most popular on this forum) did this and failed to spot the problem.
New sensor is £51.67 +Vat from BMW, I'm picking my new one up tonight.
Also just to note it is safe to drive without the TPS for diagnostic purposes as the MAF and Lambda sensors will keep the fuel mixture safe.
Cheers,
Craig
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