Throttle Position Sensor Test?

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Throttle Position Sensor Test?

Postby iwbnwif » Thu May 17, 2012 7:16 pm

Hello everybody!

I've been having problems with my otherwise perfectly behaved 45 and hoping I can find some help here :D Its a 2003 1.4i Impression S with just over 53k on the clock.

A couple of days ago the alarm went off at 5am which was caused by an almost flat battery having not been driven for 10 days.

Next day I charged the battery without taking it out of the car or disconnecting it, which was probably a big mistake. When I went to drive it, as soon as the temperature needle moved off the stop it starts bucking like a bronco. Also the idle RPM was oscillating between about 1000 and 1300.

Having read some of these forums it sounded like a Engine Coolant Temperature sensor so disconnected that and no change. Fiddled around a bit more and tried disconnecting the Throttle Position Sensor and hey presto - running smoothly again, but with high tickover still.

Reading the Rover 45 System Description and Operation, the TPS should be a 4kohm variable resistor. On mine it seems to be about 5Mohm, so suspect its faulty.... but...

When turning it manually it does smoothly and gradually increase / decrease resistance as expected across the bottom two pins, but across the top two it remains static. According to the description, I was expecting it to be a centre wiper type device like this:

+5V ----
|
|<---- variable
|
GND----

So I should see an increasing resistance across the top two pins and a decreasing resistance across the bottom two.

I wonder if anyone has a good working device that they might be able to compare with before I shell out £50 :( for a new one.

Also after stopping and switching off the engine, there is a whistling noise (has always been there and was also on my old 51 plate 1.4 Impression that I bought at 6 months old). Today I worked out this is coming from the Idle Air Control valve. I can also hear it stepping with the ignition on but the engine not running and can't think why it would do that? Disconnect the IAC and the whistling stops.

Sorry for the long post and thanks for your help!!
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Re: Throttle Position Sensor Test?

Postby rhyds » Thu May 17, 2012 7:42 pm

Hello and welcome!

Have you tried re-setting the TPS since the battery went flat? It's a pretty simple prodcedure:

1: turn ignition to "on" (so all the dash lights are on)
2: Fully depress and fully release the throttle pedal around 20 times
3: Start the engine normally

If that doesn't work then you might be right regarding the TPS being up the spout. When mine failed the car wouldn't idle properly and didn't like slow/overrun running (especially around 30mph). I swapped mine for a known good one from a spare throttle body I had, so it might be worth popping down the breakers and getting a few s/h ones.

Here's what the workshop manual has to say about the TPS:
Throttle Position (TP) Sensor

The TP sensor is mounted on the throttle body and is driven from the end of the throttle spindle. The TP sensor consists of a potentiometer which provides an analogue voltage to that the ECM converts to throttle position information.

The TP sensor signal is required for the following
vehicle functions:
• Idle speed control
• Throttle damping
• Deceleration fuel cut off
• Engine load calculations
• Acceleration enrichment
• Full load enrichment
• Automatic gearbox shift points.

The TP sensor is a potentiometer which acts as a voltage divider in an external ECM circuit. The potentiometer consists of a 4kW ±20% resistive track and a wiper arm, driven by the throttle spindle, which sweeps over the track.

The track receives a regulated 5 V ± 4% supply from pin 46 of ECM connector C0914, together with an earth path from pin 34 of ECM connector C0914.

As the wiper arm moves over the track it will connect to areas of different voltage ranging from 0 to 5 volts. The ’output’ from the wiper arm is connected to pin 20 of ECM connector C0914, to provide an analogue voltage signal.

The TP sensor requires no adjustment as the ECM will learn the lower voltage limit which corresponds to closed throttle.

If the TP sensor signal is missing the vehicle will continue to run but may suffer from poor idle control and throttle response. The ECM will store fault
codes which can be retrieved using TestBook.


As for testing, here's the procedure from Autodata:

Throttle position (TP) sensor

Component disconnected

Terminals Condition Typical value Note
1 & 3 3492 
1 & 2 Throttle fully closed 3114 
1 & 2 Throttle fully open 389  7

Notes
7. Resistance change should be smooth.
Throttle position (TP) sensor

Component connected

Terminals Condition Typical value Note
1 & 3 Ignition ON 5 V 8
2 & 3 Ignition ON - throttle fully closed 0,6 V
2 & 3 Ignition ON - throttle fully open 4,6 V 9
Notes
8. Checking supply voltage.
9. Voltage change should be smooth.


The other option is that you've somehow damaged the alternator's voltage regulator during charging. Double check that the battery voltage is healthy and stable with the engine running.
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Re: Throttle Position Sensor Test?

Postby iwbnwif » Thu May 17, 2012 9:00 pm

Hi, that is brilliant thank you.

Yes, I tried the TPS reset procedure (only 5 times and manually moved the throttle lever opposite the TPS)

I read the workshop manual description, but I haven't seen the Autodata information before.

I would be interested to see the original autodata page for this - is there a diagram showing which pins are 1,2 and 3? I am guessing top to bottom when installed, in which case mine is definately wrong because it remains static at ~ 5Mohm. Also are the typical values in ohm or kohm?

I might take a punt at a second hand one off ebay, but worried that it will also fail a bit later!
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Re: Throttle Position Sensor Test?

Postby rhyds » Thu May 17, 2012 9:06 pm

You have PM.

EDIT: Figures in Ohms (so 3kohm)
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Re: Throttle Position Sensor Test?

Postby iwbnwif » Mon May 28, 2012 11:30 am

Rhyds, I would just like to say thank you for your excellent help.

Managed to get a new TPS for £10 including P&P and everything is now back to normal, although my ELM 327 shows throttle position at 88.6% with the accelarator fully down (also tried moving the butterfly by hand).

I have tried following the recalibration procedure several times and wondered what reading other people are getting?
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Re: Throttle Position Sensor Test?

Postby Griffo » Mon May 28, 2012 11:39 am

That figure may be correct.

Somebody mentioned recently that some of the 1.4 45s have a lower power output (80ish bhp compared to the standard 103) which is limited by having a throttle body which only opens to something like 75-80%

If you take the TPS off and turn it manually whilst monitoring it you may find it will read 100%
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Re: Throttle Position Sensor Test?

Postby rhyds » Mon May 28, 2012 1:08 pm

The 84 PS 1.4 25s had a throttle that only went to 75%, but that was thanks to a different plastic cam on the throttle body.
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Re: Throttle Position Sensor Test?

Postby MGJohn » Mon May 28, 2012 3:06 pm

rhyds wrote:The 84 PS 1.4 25s had a throttle that only went to 75%, but that was thanks to a different plastic cam on the throttle body.


Yes, different ( longer ) cam and operating it manually you will still not get it to open fully. The VIN plate may give a clue as to the 84/103 engine output.
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Re: Throttle Position Sensor Test?

Postby Benny » Mon May 28, 2012 4:20 pm

Bin it and fit the 103 unit. Whos going to know?
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Re: Throttle Position Sensor Test?

Postby rhyds » Mon May 28, 2012 11:24 pm

It's only the Throttle body that's different ben, and any insurance assessor will probably check that the right TB is on before owt else.
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Re: Throttle Position Sensor Test?

Postby iwbnwif » Fri Jun 01, 2012 8:56 pm

Thanks folks!

Its not often I put my foot flat on the floor so probably it won't make too much difference anyway. Out of interest my 45 has an aluminium throttle body which I have seen mentioned is an upgrade (but that may have been talking about 400's).

Anyway the good news is its running sweetly, just put two new Firestone's on the front and had the aircon regassed!
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Re: Throttle Position Sensor Test?

Postby HH-R » Sun Jun 03, 2012 6:12 pm

Were 45s fitted with the 84 PS 1.4? I didn't think they were. My 25 used to have the engine output and trim level on a plate on the driver's (IIRC) door shut.
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