My idles hunts around slightly, i get a code 13 (oxy sensor failure) with a brand new oxygen sensor, my shift light doesn't act right, my MPGs aren't as good as they should be (16-18ish combined), and it stutters and stumbles a bit when i apply the throttle with no load on the motor (neutral).

I have an ohm meter but i dont know what the min and max resistance values of the TPS are supposed to be. If someone can tell me what those are and which leads to connect the probes to, i could just test it right now and settle this.

TPS voltage at idle (0% idle should be <.7volts and about 5volts at WOT

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Indy Northstar-Stretch ~ LT1-NOS Roadster

with the milage being so bad - I'd say new thermostat & coolant temp sensor
sounds like its not going into closed loop mode.
may take care of the stumble too - but 'prolly not

Maybe you have a bad ground.

Use a digital voltmetermeasure between terminal volts should read between .450 &1.250volts at closed throttle with key in run position ,,not running,,you are suppose to use jumper wires most just penetrate wire sheath
if you suspect bad T P S you can spray with wd 40,do not spray unless you think its bad use G.M.delco here
check grounds this effects many different components.
check idlle with all electrical off only ignition on
check Throttle body to make sure it is not carboned up ,spray clean plate area and IAC these are common cause of bad idle..many people do not check here because large rubber hose is pain to remove and replace..

Test..check vacuum line to map sensor make sure its not hardened,disconect map plug line .plug it run engine to see if it runs better..
Low freon level will make a car idle poorly when A/C or heat is on,,not all cars do this
check PCV valve a quick test is to place finger over the inlet hole and you can feel or hear the valve snap back.. when this part is malfunctioning it cloggs up the TB unit,,or you can remove it and shaketo make sure it is free.
the TPS and map are places you should only use GM parts..
if rough idle occurs only during warm up or when engine is cold or much more pronouced when cold it is probably fuel related ..
any time a rich condition is supected you pull a vacuum hose and force a lean condition use finger as controll..

Okay, tested both of my TPS units. the one on the car has a range between .77V and 4.16V, my spare has a range between .83V and 4.48V. The spare has a wider range with the WOT closer to 5 volts (alot closer) which is where it's supposed to be according to Fiero 2M8 (who is getting a + BTW, stan and Pyrthian already had a +)

I will switch to the spare and see if it improves

quote Originally posted by MordacP: Okay, tested both of my TPS units. the one on the car has a range between .77V and 4.16V, my spare has a range between .83V and 4.48V.

Did you make both your measurements with the TPS mounted on your TB or off of it? If you measured while they were mounted, it's possible you just need to bend the "tang" to get either one or both within spec.

[This message has been edited by Patrick (edited 03-12-2009).]

Closer to 5.0 is better ..it is difficult to get the readings unless you have excellent digital unit .. I do not fully understand how this works ..I hope the replacement unit works for you ..I thought the problem was in the throttle body ,Im not afraid to stick my neck out !! its heavily scared . ha ha let us know

[This message has been edited by uhlanstan (edited 03-12-2009).]

quote Originally posted by Patrick: Did you make both your measurements with the TPS mounted on your TB or off of it? If you measured while they were mounted, it's possible you just need to bend the "tang" to get either one or both within spec.

I measured it while it was mounted on the TB and I bent the tang to get it where i wanted. I couldn't find any adjustment to get it within the specs that 2M8 posted, the range of values on the TPS is just too narrow so I got it pretty close in between. Would a new one have a wider range? One funny thing was that it was 4.2V when it was closed and .8V when it was open which is backwards from what Fiero 2M8 said (.7 idle and about 5 WOT) is he mistaken or is my TPS just screwy or was i probing the wrong wires(i bet that's it, i was probing the top and middle wire)?

quote Originally posted by Stan the Man: ...Closer to 5.0 is better...

i went the other way here, i adjusted so it was would closer to the .7V value when it was wide open because it would be more accurate on the free way when i'm using more throttle.

quote Originally posted by MordacP: One funny thing was that it was 4.2V when it was closed and .8V when it was open which is backwards from what Fiero 2M8 said (.7 idle and about 5 WOT) is he mistaken or is my TPS just screwy or was i probing the wrong wires(i bet that's it, i was probing the top and middle wire)?

I use WinALDL to check my TPS voltage, but it's been awhile since I've done it. Seems to me though that the smaller values were for idle, and I also seem to recall that it wouldn't quite make it to 5V at WOT.

I've noticed today that it idles around 2000 when it's cold in the morning and wanders between 1500 and 2000 while it's warming up. I dont think it's a fuel problem because it starts up very easily so no leaky injectors. I will check my coolant temp sensor. Could this be a symptom of a faulty MAT sensor?

quote Originally posted by MordacP: Did more tests on my coolant t-stat, coolant temp sensor and MAT sensor.

Again, this is where WinALDL comes in so handy. When used first thing in the morning when the engine is cold, WinALDL should show that both the manifold air temperature sensor and the coolant temp sensor will read the same temperature at startup. If not, one (or both) of the sensors isn't reading properly.

quote Originally posted by Patrick: I use WinALDL to check my TPS voltage, but it's been awhile since I've done it. Seems to me though that the smaller values were for idle, and I also seem to recall that it wouldn't quite make it to 5V at WOT.

You are correct Patrick and ~4.5volts WOT is fine.
If the idle TPS value is higher than .7v the ECM will think that more than 0% throttle is being used.
BTW - When I bought my 350, someone had stuck a 305 TPS in the throttle body that was designed for the other side.
That caused the voltage to read backwards - what a pain to find that problem!

Here's some more info on Fiero TPS sensor:
http://stoney.lizardmaster....rticles/OSG/TPS.html

MordacP - I don't think that's your sole problem with the idle hunting:
Read the GM unstable idle (page B7) and hesistation (page B3) below to get more ideas of what to check:
http://members.shaw.ca/corv...6E3-B%20Symptoms.pdf

It could be vacuum leak (check at idle with a vacuum guage) if your idle is at 2000rpm cold or a MAP sensor issue (see link) :
http://www.pontiacperforman...les/MAP_Upgrade.html

A scanner might be a great investment because you could then report the sensor data to everyone and get more feedback/help.
Also it would help if you told everyone the details of your Fiero (year, engine, trans etc)
Cheers,
Ryan aka Fiero2m8