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E34 (1989 - 1995)

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Old 11-13-2012, 04:19 PM
robertobaggio20 robertobaggio20 is offline
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Safety warning : Bad TPS causes sudden engine cut-outs

Hi Everyone,

I encountered a fellow E34 owner in 3D who had a problem that was familiar....too familiar. Then I remembered. I had this problem a couple of years back. It was fixed before I joined the fest and thus remained forgotten, until now.

My comments refer to the M50 engine but I don't imagine why they wouldn't apply elsewhere so please note.

A buggy throttle position sensor (tps) can sometimes lead to engine cut-out situations, and seems to happen most often when the car is making a turn. It cut out on 2 u-turns for me. And once, I was speeding toward a highway's exit and the engine cut out ! Power steering died and brakes got on life support immediately but quick thinking and Total Self Confidence enabled me to negotiate the turn without any harm to me, other road users, or my car. It is amazing you can turn into a superdude when you're put on the spot and you don't have time to think doubt in.

So as I was saying, the E34 owner I met had this problem too. The car would cut out while in traffic, and when being driven slowly, and while making turns. Their mechanic had tried everything, changed everything, read all the damn codes, problem had not been fixed for weeks. As they lamented about this, I remembered what happened on my car. Lo and behold, I had a spare good used tps in my trunk ( I had put it in there just 3 days before!) and I handed it to them.

To my recollection, there has been only one person here who had the same symptoms and it was traced to the same problem. So this is an obscure issue to be sure.

The engine will always restart after it cuts out. You may or may not have an error code stored in your car as a result (I don't know why it works this way as yet). These are my direct observations.


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Unfortunately new ones don't seem to be cheap :

http://www.ebay.com/itm/BMW-Throttle...-/110728789876

And used ones are not worth buying.

So, if cash flow is real tight, then at least do the following until you can invest in a new tps:

1. Check the bentley manual. It has a section on this and will show you how to test your tps's resistances. Ensure that everything is in order.

2. Clean your tps's connections on both the tps and its connector. Use contact cleaner and a toothbrush on the tps's prongs itself. Let the cleaner dry, apply dielectric grease on both the connector and the tps's prongs, and reinstall.

3. At least purchase a good used one to keep as a spare. I just saw one on ebay for $25. Once received, check its resistances, then install it into your car and make sure it works, then keep your old unit as the spare. When cash flow improves, get a new one and put up at least one of the used ones for sale.

The tps itself is real easy to swop out. A short screwdriver and 10 minutes. No torquing down needed.

A buggy tps can also lead to idling problems and hard shifting (the transmission ecu also uses tps signals to determine shifting points). These issues are obscure but they do happen. So getting a new one may be useful in others ways as well.

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I'm putting this out there because a buggy tps CAN and HAS caused engine cut outs at both low and high speeds, which also cuts power and vacuum to your steering and brakes, and that is just dangerous. And this is a 20 year old car...nothing in it is new unless you replaced it yourself.

That being said, this is an E34. Its cheap to begin with, you're buying it because you're making a lifestyle choice and not because that's all you can afford, and with the help of the manual and the forums, you can deploy your resources efficiently. So please get yourself a new tps, it is a safety issue on our old, high mileage cars.

And yes, even mechanics would do well to change their tps's out. If you are a mechanic and you think that this is a waste of time, I dare you to show this post to your missus and have a good night's sleep thereafter.


rgds,
Roberto

Last edited by robertobaggio20; 11-13-2012 at 04:49 PM.
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