UPDATE IDLE HUNTING -Test a faulty TPS(sorted see post 15)

[Jibs05 86]

Hi all,

(copied from my build thread)

So i did some tests the other day on the electrics/sensors with his multimeter that is a lot flasher than mine,

the coils came back reading good, and so did the crank angle sensor and cam position sensor. so i was standing around kinda clueless as to why it did so bad at the dyno.

I checked the TPS, and at close (around 1.3ohm), to half throttle (2ohm) it reads resistance fine until i turned it just past half way. kaka. reads nothing.

Online (because its sooo reliable) has told me to look for 1-4ish ohms. Does this sound about right for a faulty TPS?

Or am i doing it wrong?

cheers!

---------------------------------------------------------- update ----------------------------------------------------------

1/11/2014

Hi all, put in some 21lb injector for my m50b30 stroker. Naturally it would hunt for idle because the tune isn't right(haven't been driving it, maybe one pull up the street then parked up).

So I purchased a chip from Euro-tuning specifying my modifications, installed the chip, reinstalled the ECU and started it up. Waited until it was near operating temperature, but its still hunts for idle. Although it does run more consistent than before and less smoke out the exhaust.

question is could my o2 or AFM be reading wrong(broken)?

I honestly don't think the chip is bad, but then again, I don't know enough about chips to make that assumption.

Here is a video of what is happening at the moment...

you will see at the end of the video i look at some black liquid on the ground, it has the consistency of water but looks black. Is it because it has been parked for a while? (2-3 weeks)

thanks for any help!

Edited November 1, 2014 by jkhan05

[KwS 2425]

i was under the impression you tested TPS with voltage (between 0-5v), not resistance?

[thorburn 121]

what engine and how are you testing?

[Auzeras 28]

Yeah, I can't remember the specifics but a TPS isn't a potentiometer or simple variable resistor so simply ready the resistance won't product a nice smooth curve.

I think (as 4th gear suggests) you're supposed to test it under working voltage and measure the received current. If I recall correctly that's not exactly perfect either and a "proper" test involves graphing the resistance and return voltage against each other.

I'm pretty sure an 88 E30 uses a similar TPS to an 89 E32 - I'll try find the documents on TPS testing and link them, they are for the E32 I think but should be a similar process.

[Jibs05 86]

Mine reads 1.32 - 4.25 over the full range and operates correctly, I've compared it to a known good one.

Ok cool! Is that resistance or voltage?

i was under the impression you tested TPS with voltage (between 0-5v), not resistance?

Oh? The world wide web told me to test resistance?

what engine and how are you testing?

Sorry should have mentioned this is on my project e30 with a M50B25 non vanos and 402 ecu

Yeah, I can't remember the specifics but a TPS isn't a potentiometer or simple variable resistor so simply ready the resistance won't product a nice smooth curve.

I think (as 4th gear suggests) you're supposed to test it under working voltage and measure the received current. If I recall correctly that's not exactly perfect either and a "proper" test involves graphing the resistance and return voltage against each other.

I'm pretty sure an 88 E30 uses a similar TPS to an 89 E32 - I'll try find the documents on TPS testing and link them, they are for the E32 I think but should be a similar process.

Sorry should have said this was on my e30 with a M50 engine

[Auzeras 28]

Just in case it's not a TPS here's a quick "symptoms check" -http://www.bimmerboard.com/forums/posts/1081877 Note the value given in resistance are NOT indicating that there should be a linear or exponential scale between them, just at those positions those approximate resistances may be read. Anything drastically out may signal a problem.

All good with the M50, that was run until early '96? Similar systems I think in terms of TPS technology. Things haven't changed a hell of a lot since then.

Here's what I got from a few pages:

With the IGN ON - Test for +5v on the TPS harness from the engine, if it's not getting a good 5v there is another electrical problem causing the TPS to give out wrong data. Not sure which pin it is, but just take the + lead and probe each one to see what ya get. Get the other pin on a good ground. If you get an out of spec reading then try the - lead on another ground as it might be that that's causing the bad reading. Pays to be sure.

With IGN OFF check resistance between the TPS harness +5v pin and the DME/ECM (again you'll have to check your schematic for this) resistance should be less than 5ohms. Repeat for the common or ground wire on the TPS, if your TPS uses the chassis to ground itself then make sure it's seated cleanly.

IGN ON again - Reconnect TPS to the harness and some how work out how to probe the TPS signal wire with the sensor connected. This can be tricky, might be best to run some jumper wires from the harness to each pin of the TPS minus the signal pin which you'll probe + lead to signal wire, - lead to good ground.

That last one can be done off the car or disconnected if you have a good 5v source. You'll need to work out which pins are +5v and Ground/common and which one is the signal wire. Anyway hook it up and see if you get a nice reading of between 0.5v to 4.5v

IF the voltages are correct then there is a problem elsewhere. Most likely to be with DME/ECM but could be elsewhere. Never assume with these damn expensive computers!

Hope this helps & the info is accurate!

[Auzeras 28]

This is a nice write up http://www.enduringautomotive.com/tps/

- None of this info covers a 5 or 6 pin TPS... don't have any info on them

[Ahmedsinc 414]

Just further to this, does anyone know if the TPS is the same on Vanos and non - Vanos M50B25?

Wondering if this might be the unicorn I've been searching for..........

[Jibs05 86]

Just in case it's not a TPS here's a quick "symptoms check" -http://www.bimmerboard.com/forums/posts/1081877 Note the value given in resistance are NOT indicating that there should be a linear or exponential scale between them, just at those positions those approximate resistances may be read. Anything drastically out may signal a problem.

All good with the M50, that was run until early '96? Similar systems I think in terms of TPS technology. Things haven't changed a hell of a lot since then.

Here's what I got from a few pages:

With the IGN ON - Test for +5v on the TPS harness from the engine, if it's not getting a good 5v there is another electrical problem causing the TPS to give out wrong data. Not sure which pin it is, but just take the + lead and probe each one to see what ya get. Get the other pin on a good ground. If you get an out of spec reading then try the - lead on another ground as it might be that that's causing the bad reading. Pays to be sure.

With IGN OFF check resistance between the TPS harness +5v pin and the DME/ECM (again you'll have to check your schematic for this) resistance should be less than 5ohms. Repeat for the common or ground wire on the TPS, if your TPS uses the chassis to ground itself then make sure it's seated cleanly.

IGN ON again - Reconnect TPS to the harness and some how work out how to probe the TPS signal wire with the sensor connected. This can be tricky, might be best to run some jumper wires from the harness to each pin of the TPS minus the signal pin which you'll probe + lead to signal wire, - lead to good ground.

That last one can be done off the car or disconnected if you have a good 5v source. You'll need to work out which pins are +5v and Ground/common and which one is the signal wire. Anyway hook it up and see if you get a nice reading of between 0.5v to 4.5v

IF the voltages are correct then there is a problem elsewhere. Most likely to be with DME/ECM but could be elsewhere. Never assume with these damn expensive computers!

Hope this helps & the info is accurate!

This is a nice write up http://www.enduringautomotive.com/tps/

- None of this info covers a 5 or 6 pin TPS... don't have any info on them

wow all that info! thank you! Obviously my search skill aren't as good as yours!

Impedance (resistance) for sure.

I'm not sure you should be measuring V+ for a TPS, it could work I suppose but it would only be approximate. (I'm open to be schooled here!)

Edit:

Despite everything said above (by everybody) if your sensor is not providing an accurate reading between _any_ range and especially if is providing *no* reading at *any* point then it is faulty. Ohms or V+ is irrelevant in these cases.

It is reading 1-2 ohms just till around half throttle, just past half it will read dead.

Just further to this, does anyone know if the TPS is the same on Vanos and non - Vanos M50B25?

Wondering if this might be the unicorn I've been searching for..........

Im hoping this for me too, if its mechanical... another can of worms.

[Ahmedsinc 414]

Im hoping this for me too, if its mechanical... another can of worms.

Ditto mate, have had a weird 'flat spot' between 2700-4000 rpm for a while but hadn't thought of TPS til I saw your thread. Slightly surging idle sometimes too.

I cbf testing the one in the car now, but I do have one from an NV motor that I can throw at it and see (hope) it fixes the problem

[Jibs05 86]

If you have the TPS in situ then you should measure voltage, the operation should be either linear or logarithmic ( don't know specifics)

and you should read a proportional change in voltage as you operate the throttle, no gaps dips or significant variations.

IF you have it out of circuit then you can measure the resistance and you should equally measure a proportional change in resistance as you operate the device through its full range.

Two simple tests just pick the one that is appropriate - for Voltage the key needs to be on .

P.S. measuring with the engine running is sub optimal

"There are 3 prongs on the tps. Put one of the leads on the first prong and one of the leads on the last prong. You should get approx 4K ohms. Next, touch the leads to prongs 1 and 2 while rotating the throttle plate from the fully closed to fully open position. The resistance should flucuate from 1K to 4K ohms."

that's the test i did yesterday, although i didn't get the 4k ohms.

will try the voltage (in situ) test tomorrow afternoon and report back!

cheers!

[Jibs05 86]

Ok, did the voltage in situ test

TPS location (has yellow dot on it)

Remove the cover

And with the ignition on (engine not running) I tested the voltage to the TPS while opening the throttle slowly

So i think i have good voltage at the TPS. As 3pedals (Ron) said, there weren't any gaps or inconsistencies when operating the throttle with the multimeter in.

Anything I've missed?

[Jibs05 86]

You use the word "fluctuate" if what you mean is it changed progressively then it appears okay , if it fluctuated it means that the change was not progressive. - please clarify.

You should measure 4kohms end to end , you should measure a varying value between an end pin and the wiper (active) as the throttle is operated

If when you measure voltage you had the correct voltage at the hot end and a progressive change on the wiper then it suggests it is okay.

measuring voltage can be more reliable than resistance

OK mate. Just quoting what you said in your words so i could convey an understanding of what i was implying. The change in voltage was progressive.

[Jibs05 86]

Thank you

[FRT 144]

Easy to pop appart and clean potentiometer sweeper with some IPA. Make it go betta :-)

[Jibs05 86]

Easy to pop appart and clean potentiometer sweeper with some IPA. Make it go betta :-)

oh wow thanks! Probably do that today!

Rather than starting a new thread ill update this one

1/11/2014

Hi all, put in some 21lb injector for my m50b30 stroker. Naturally it would hunt for idle because the tune isn't right(haven't been driving it, maybe one pull up the street then parked up).

So I purchased a chip from Euro-tuning specifying my modifications, installed the chip, reinstalled the ECU and started it up. Waited until it was near operating temperature, but its still hunts for idle. Although it does run more consistent than before and less smoke out the exhaust.

question is could my o2 or AFM be reading wrong(broken)?

I honestly don't think the chip is bad, but then again, I don't know enough about chips to make that assumption.

Here is a video of what is happening at the moment...

you will see at the end of the video i look at some black liquid on the ground, it has the consistency of water but looks black. Is it because it has been parked for a while? (2-3 weeks)

thanks for any help!