I've got a code 21, and I was kind of foggy on the procedure for adjusting the TPS. Anyone know how to do it with a VOM?

 

As far as I know the TPS (Throttle Position Sensor) adjusts itself? I have taken mine out and cleaned it off with parts cleaner as well as cleaned out the throttle body with TB Cleaner, but as far as I know it sets itself. If you do a search I'm sure you would turn up a lot of information about it.

 

i've never heard of a self adjusting TPS. you must check the voltage on the three wires going into the sensor. *note* the sensor must remain plugged in during this process, i've heard of people who have unplugged it then wondered why they can't get any voltage from it. there is one wire that is the power, it will show five volts. *note 2* use paper clips straightened out of something to push in the plug next to each wire. the other two wires, the voltage will change as you gradually increase the position of the throttle. do this with the key on but the engine off. voltage across these two wires at idle should be about .54 volts and gradually increase to about (i think) 4.75(?) volts at WOT.

 

We need the year of Jeremy's car.

85-89 = TPS not self adjusting
90-92 = TPS self adjusts

 

it's an '89

 

90-92 self adjusts?? i didn't know that. how come my 91's tps is a little off (not far but a little)?

 

I keep reading on how to check the TPS, but if it is off, how do you adjust it?

 

Loose the two screws and turn it while watching the meter.

 

okay, I just plugged the moniter 4000 into the car and did it that way

 

I did it today and tightened the screws down when the voltameter read between .4-.5....that's the best I could get it to read. Then I went to start the car and it was idleing at 1,500 rpm!! So I had no choice but to put the TPS back to the original spot. So what does this mean? Do I need a new TPS? Thanks guys.

 

AGood2.8- sorry, maybe I'm a little slow, but I don't understand what you're showing in those pics.

 

he's just showing how the tps can move.

 

my guess is to get it at the right voltage, then adjust your idle to that. check your IAC to see if its bad. I believe to check for bad TPS you just slowly open the throttle to wide open, and make sure the voltage climbs steadily to between 4.0 - 5.0 volts.

 

I just had a new AC delco IAC valve put in. I don't understand why the TPS isn't at the correct voltage. I mean, if it's to the point where I have to move it, which throws off the idle, then doesn't that mean I need a new TPS all together? It seems to me that moving it around to get a better voltage is "covering up" the problem....maybe I'm wrong. I just need to get better than 11 mpg.

 

you checked you O2 sensor? that can cause bad gas mileage.

 

I had that replaced the same time I had the IAC done....a genuine AC Delco... Still getting 11 MPG

 

Woah, wait, don't try to fix your idle by setting your TPS at an incorrect voltage!! Put the TPS to the spec listed for your v8 TPI IROC. If the idle is still high, there's a problem elsewhere. You might have to reset the idle. By screwing with the TPS to get the idle where you want it, you're just masking the real problem.

See the "IAC and TPS adjustment" article in the thirdgen.org tech section, https://www.thirdgen.org/newdesign/tech/ , for info on all of this.

Like Jeremy178 said, the way to check for a faulty TPS is to watch the meter as you open the throttle from closed to wide open. However, the best way to do this is by using an analog meter. You can NOT hook an analog meter up to the ECM harness though! You'll need to keep the ignition off and unhook the TPS plug. Set an analog meter to the ohms scale, and put your probe to the middle TPS pin, and to one of the upper/lower TPS pins (I forget which, upper or lower, but results should be the same). You'll see resistance on the meter. As you watch the meter, move the throttle slowly. The meter's needle should swing gracefully- no jerks or jumps.

This can't be done with a digital meter because the digital meter takes a "sample" every few milliseconds. For instance... let me bring this out of the milliseconds. Say you've got a meter that samples once every 5 seconds. If your value is steadily increasing over 30 seconds, your meter will only show you 6 new values. And that would seem like a "jumpy" readout. Analog meters show instantaneous values, and the only "jumpy-ness" would come from a bad sensor.

 

Yeah, like I said, I put TPS back to the exact place I moved it from (because I marked it on the TB). I don't have acces to an analog gauge. Today it surged twice pretty bad when I was sitting in traffic. So I think I will go ahead and replace the two Maf relays since they are fairly cheap, and go from there. If I still have a problem, I will consider getting a new TPS.

Yesterday when I checked the TPS, I could not EVER get a .5 reading....the highest I could get it to read was .4. I still don't really understand what the maf relays would have to do with the idle and bad mpg, but I'm just going by what others have said on here. I just got gas a few minutes ago, and I figured 11.9 mpg, up a little and still consistent, so that's a plus....now I just need to find the problem.