Throttle Sensor? Brake Sensor? Something Electrical is causing surging idle :( please help

Ksmillie1987 · Post by **Ksmillie1987** » Thu Mar 21, 2019 6:17 am

Hey guys - this is my first time posting. After an extensive search on multiple topics revolving around Throttle Sensors all the way to MAF and the Brake/Stop light switch. Ive learned a ton about how the systems work.

I cant seem to track down the main cause of my problems although I feel I am closing in on it.

Ive got a 2003 Z4 2.5 with 146k on the clock (manual 5 speed)

my foxwell obd2 has been giving me some weird readings while trying to track down a LTFT +20 avg issue. (both banks) when idle.. highway speeds it comes down to about +10 ltft... my stft bounces from -2 to 8 usually

Replaced Plugs / Coil packs / new ICV / cleaned Throttle Body / new Injectors / switched to catch can at first but now have a new CCV system installed. Whole new Intake Boot. and a nice new battery

and pre cat 02 sensors and a HPFR

seeing that I replaced these items thinking i had a vac leak- i made a home made smoke tester and have ran several tests and the system is sealed.

One code i am getting depending on outside temp is the secondary air injection which i have not fixed yet. (but the one way valve under the air pump is working and doesnt let exhaust pulses out.
I dropped the exhaust and replaced the High pressure Fuel components filter/reg etc. trying to rule out the hard starts and fuel issues.

heres the issue that has me stumped

My original MAF sensor is dead I believe... it reads .01lb at idle and only changes when aprx at 3-4k on highway. So I put a MM on it and the OHM reader tells me its lacking compared to a new MAF.

Ive bought new mafs both cheapy and OEM and they do the same thing .
when new maf is installed my idle surges when applying the brake . from 700rpm to 1200rpm up and down steady.

Next i read on this forum that the Brake Servo could be the culprit. SO i disconnect the sucking jet line from the booster and low and behold... the problem STILL HAPPENS.

Ive tracked this issue to the very second the electrical signal happens from the brake switch is when it occurs.

my throttle position sensor could also have a part in this because my TPS% usually stay at 0 or are all over the place from 3 - 35-18 then to 8. which would explain the car taking 2-3 attempts to start.

my question is --- could this issue be a voltage regulator issue? seems when the idle hunting begins the radio roof and AC button lights dim down ever so slightly.

or a Throttle sensor issue - because my gas mileage has dropped and its hard to start with varying fuel trims in the positive (not to mention the live data readings all over the board TPS%)

or a brake sensor causing some type of short which causes a chain reaction with the tps and maf.

i have no engine vacuum leaks from my smoke tests - engine hard to start but runs great afterwords.

when accelerating - i get a bit of a stutter around 2k and 1500k --- just a flicker . also if i let off the pedal to coast down from 3500rpm she floats around 2k and 1500 then continues down to idle.

I am running with the original maf right now which has no idle surge when braking... all these issues pop up when putting a (working MAF) into the car. and yes ive tried several different ones.

SORRY this post has been so long - this has been a perplexing issue with tons of forum searches and tons of replacing parts thus far.
My MM readings at the battery (which is also new) reads optimal and slightly up after the car is running but not too much.

Thank you all for taking the time to read this --- im leaning toward electrical issue of some type whether it be alternator voltage . brake. or pedal. but i need your help-

thanks all have a great night

Trav · Post by **Trav** » Thu Mar 21, 2019 10:07 am

You know it happens with your brake switch. Very odd. With ignition on and enigine not running what do you see on your OBD when you use it to monitor voltage and sensor readings when you press the brake? That should take the voltage regulator in or out of the game as it's on the alternator. The brake switch circuit will be on a relatively small fuse. A car battery is a powerfull thing if you short it, I think the fuse would blow. If you have a quiet road, disconnect the brake light switch and take it for a short run.
That should be enough to prove or discount this bit I think.

Ksmillie1987 · Post by **Ksmillie1987** » Thu Mar 21, 2019 3:15 pm

Trav wrote: ↑Thu Mar 21, 2019 10:07 am You know it happens with your brake switch. Very odd. With ignition on and enigine not running what do you see on your OBD when you use it to monitor voltage and sensor readings when you press the brake? That should take the voltage regulator in or out of the game as it's on the alternator. The brake switch circuit will be on a relatively small fuse. A car battery is a powerfull thing if you short it, I think the fuse would blow. If you have a quiet road, disconnect the brake light switch and take it for a short run.
That should be enough to prove or discount this bit I think.

I thought it very odd as well.... only with a new maf in the surge was so reliable to show up i just started narrowing it down... if i step on brake it rises up slow and if i take my foot off "right at that switch point" it will drop down to idle quickly. if you hold your foot down near the switch point of the brake pedal and just click it on and off you can def tell that is the cause..(maybe not the source) but def the trigger point.

unfortunately i need a better monitoring system... i have a foxwell scanner that doesnt go that into detail for electrical while plugged in to obd2 port. all my electric metering thus far has been with multimeters.

as far as disconnecting the brake fuse - i did think of that a few days ago... found 4 fuses behind glove box... pulling any of the 4 seemed to make the car not turn over at all as if there was a fail safe mode.

i will try again just to be sure and be specific..... i just had this crazy theory that maybe one of these three (throttle, stop switch, voltage reg) is dying and making a mystery out of them all in a domino effect.

Ksmillie1987 · Post by **Ksmillie1987** » Thu Mar 21, 2019 3:27 pm

my poor maf that is original but worn out - from what my scanner shows is trying to work at higher road rpms (fuel trims go back down.. maf readings go up etc etc)

quick update as of this morning

i was trying to re create the problems with my throttle sensor finding ranges where the tach was floaty or had a hiccup. ive also found the car drives way better concerning this problem while having the sport mode on. its much easier to re create these issues with sport off... which makes me think the problem is the throttle position sensors.

ive had lean codes and misfire codes and maf codes(air input low volt and air temp high volt) throughout this process but this morning i got something different.

as i was hunting for the throttle issue sort of waving the throttle up and down ... it threw a code.
this code couldnt be read though.... so i plugged my bluetooth reader with FIXIT app and it threw a different type of warning up there which stated possible computer issues.. *never through EML* but threw a code that 2 different readers had no clue on besides warning me it could be a problem with a main system.

This also leads me back to voltage regulator - becuase i was practically surging the car up and down looking for throttle problems and watching how dim back and forth the radio and button lights would go. this code was thrown before months ago but i paid no attention... it cant be read but it can be reset.

my foxwell just acts like theres no code there but will reset it

my cheap BT FIXIT app actually relates the code to an onboard computer issue ecm blah blah... but its still a mystery

if it happens again i will def snap a shot of it and post it... i hope my car brains arent gettingready to go.. hopefully its one culprit causing all of this

ph001 · Post by **ph001** » Thu Mar 21, 2019 3:34 pm

If you haven't changed the battery then this would definitely be the next step. I'm not saying it's going to fix it but you certainly need to eliminate it. It's important the the battery is in good condition (i.e. low impedance) for the electrical systems to function properly. It's no good just testing your battery for volts or even just capacity - you need to make sure that when a high load is taken off it that the volts don't drop too much.

Once that is eliminated you need to check the voltage at the charge points under the bonnet with your multimeter when you are pressing the brake on and off (just your ignition on and car not running). This will tell you if any of the wiring from the battery to the engine is bad. Then repeat the test with the engine running.

This could be an earthing problem in the rear lights (that has come up before on here) - when that happens it pushes the current through other ancillary items to get to earth and causes all sorts of weird screwy issues. You do tend to find that the brake lights aren't as bright as they should be though.

Ksmillie1987 · Post by **Ksmillie1987** » Thu Mar 21, 2019 4:29 pm

ph001 wrote: ↑Thu Mar 21, 2019 3:34 pm If you haven't changed the battery then this would definitely be the next step. I'm not saying it's going to fix it but you certainly need to eliminate it. It's important the the battery is in good condition (i.e. low impedance) for the electrical systems to function properly. It's no good just testing your battery for volts or even just capacity - you need to make sure that when a high load is taken off it that the volts don't drop too much.

brand new battery - glass matt = high price

ph001 wrote: ↑Thu Mar 21, 2019 3:34 pm check the voltage at the charge points under the bonnet with your multimeter when you are pressing the brake on and off (just your ignition on and car not running). This will tell you if any of the wiring from the battery to the engine is bad. Then repeat the test with the engine running.

never thought of checking those with engine off as well - i will def do this

ph001 wrote: ↑Thu Mar 21, 2019 3:34 pm This could be an earthing problem in the rear lights (that has come up before on here) - when that happens it pushes the current through other ancillary items to get to earth and causes all sorts of weird screwy issues. You do tend to find that the brake lights aren't as bright as they should be though.

i think your on to something here - while changing the rear passenger brake light- the housing had a black burn mark on the plastic inside -- this makes perfect sense- when my blu tooth receiver is connected i can hear a motor tick that increases speed with throttle. sounds like ignition ticking through door speakers- bad grounding

i will check into the rear brake light- the old one was burnt out but the new one hasnt burnt yet... but the black spot was in the housing where connected to the base of the bulb

Ksmillie1987 · Post by **Ksmillie1987** » Thu Mar 21, 2019 11:17 pm

Ok- so I tested posts under bonnet and starter/ jump post were both good at 16v while engine idle

Battery was also sitting at 16v at idle. Maybe 17 was highest it got around 3500rpm

Both pics are of an old sub system previous owner had that fuse was blown - I disconnected this
Bulb housing which I referred in original post is rear left brake light. Also removed for testing - works good now with new bulb

None of these issues fixed the idle surge when brake switch is activated.

I did pull connecter to throttle body and volt tested it- it’s 6 prong - all prongs were 0 except 1 which was 6v ... another was reading like .5v and bounced a little I could barely get anything out of it. (Key position 2 power)

Ksmillie1987 · Post by **Ksmillie1987** » Thu Mar 21, 2019 11:24 pm

https://youtu.be/7iOLz6i5ewo

The clicking sound is ONLY when my Bluetooth fm transmitter is on powered through the cigarette lighter

ph001 · Post by **ph001** » Thu Mar 21, 2019 11:52 pm

17v is way too high for the battery... somewhere very amiss there. Are you sure your meter is ok?

Ksmillie1987 · Post by **Ksmillie1987** » Fri Mar 22, 2019 5:51 am

ph001 wrote: ↑Thu Mar 21, 2019 11:52 pm 17v is way too high for the battery... somewhere very amiss there. Are you sure your meter is ok?

.
https://youtu.be/7iOLz6i5ewo ---- is the video of the surging problem.. wasnt sure if the first link worked

ive got two styles of multimeters - i will try the digital one tomorrow. it appears to be in between 16-17 while the car is running.

i do have a question about the throttle sensor... i cant seem to find the throttle position sensor for the 2003 e85 2.5L online or at any parts store. ive read some info saying that this model would need either a new pedal assembly or a new throttle body? closest thing for my model is a sensor connector that is 15 dollars and looks like a bare wire pigtail.

only thing that comes up is for 2006 or later models which appears as an actual 3 prong sensor.

so if i need to fix this TP% issue i would need a new pedal with a sensor built in?

thanks ph001 for your help so far

Ksmillie1987 · Post by **Ksmillie1987** » Fri Mar 22, 2019 5:57 am

also - i attempted to pull the Positive terminal from the battery while the car was idling. she ran just fine until about 3-4 minutes had passed and flat out died out of nowhere. The alternator kept the vehicle running at idle which is what I have read to be a test of the alternators output capacity.. for it to completely die after several minutes without warning im not sure is normal.

I drove her about 100 miles round trip today visiting my grandma in the hospital and she ran amazing at higher speeds and rpm... even with a dead maf it feels like the car has attempted to adapt. once i get this mystery issue fixed then I will be able to put the fresh new Maf in and lower my fuel consumption fingers crossed!

average time of cranking is 4 seconds.. sometimes a few more sometimes a few less. I have been trying to push the sport mode button before cranking the starter and pushing the throttle in and out to see if it helps - but im not even sure if the actuator is opening the throttle plate before the engine is actually on

Trav · Post by **Trav** » Fri Mar 22, 2019 8:38 am

You need to change your voltage regulator. If you see over 16V it will stsrt shutting modules down probably. You may normally get 14.5 or so on your MM but not 17. That is definitely high. The voltage should regulate well with the load so unless you have fitted some funky kind of battery the regulator is knackered. Or your MM is. If you dont mind me saying, you are getting frustrated, slow down and try to properley eliminate 1 thing at a time. You have to be able to trust your test gear before testing anything.

Trav · Post by **Trav** » Fri Mar 22, 2019 9:05 am

I also noticed in your second picture a metal thing with the word kicker on it. Not being down with the kids I had to google it. Do yo have a stupid big amp in your car? Sorry you do. I see it now referred to a sub system. Thats what probably fried your regulator. If you trust your MM that is.

Trav · Post by **Trav** » Fri Mar 22, 2019 10:31 am

Also may be the rectifier on the alternator itself. See if you get any A.C. ripple with the engine running. Should be clean D.C.

Ksmillie1987 · Post by **Ksmillie1987** » Fri Mar 22, 2019 7:30 pm

Trav wrote: ↑Fri Mar 22, 2019 9:05 am I also noticed in your second picture a metal thing with the word kicker on it. Not being down with the kids I had to google it. Do yo have a stupid big amp in your car? Sorry you do. I see it now referred to a sub system. Thats what probably fried your regulator. If you trust your MM that is.

I agree with you completely! the previous kid who owned the car had an amp and subwoofer system. everything was removed except for the lead and fuse that was still hooked on to the positive terminal ... i removed it shortly after taking that pic.

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