my hayne's manal says to set the TPS in such a way that the lever on it is pressed down far enough to read .54 - .56 volts on a voltometer. In order to do this though the lever on the side of the TPS has to be almost halfway pressed down. I cant even set it in the vehicle tilted enough so that at idle the lever is pushed down that far be cause the positioning of the bolts is in such a way. HOW am I to set the TPS in at such an angle that I pull readings of .55 volts?? (I get the reading by running 3 wires from the sensor to the plug and stripping a part in the middle of the 3 plugs, then I read the top and middle wires circuit voltage.) In order to pull a .55 I have to have the lever on the side of the TPS pulled down approximately a half inch from its rest point, am I not calibrating/reading this correctly?? By having it moved a half inch the TPS is facing upward at approximately a 45 degree angle (also weird, since everyone else's seems to point reletively straightforward) I've been trying for about 4 hours to get it to read right and rest in the right spot, WHAT DO I DO TO CALIBRATE MY TPS!? I have a 2.8 V6 automatic with A/C and P/S... no A/P.... just in case it makes a difference. PLEASE HELP ME

 

The TPS voltage is read with a digital volt meter negative to ground and positive to the middle wire on the TPS. I don't think the TPS voltage is adjustable (I could be wrong). If you've had the TPS off of the TBI (it is TBI isn't it?), the lever that moves may not be hitting the correct part of the throttle shaft. If it's an MPI system, the same thing could be wrong. A picture would be helpful.

 

nope - the dreaded MPFI.. i know how to take the readings, it just seems that in order to get the required reading (.55V) the TPS has to be held out of position

 

Have you adjusted the throttle plate min air rate?

 

Theres screws that hold your TPS in place. Theres rainbowshaped holes in the tps so it can be moved around like loose goose and adjusted. Back off on the screws a bit and pysically move the tps to 5.55 (my sweet spot). Tighten and test it out. maybe no solvent, or your coughing up 40 buck or 23 off the net.

 

yea i know that's how it's supposed to be adjusted, the problem is in order to pull the right number (you set yours at 5.55?? mine haynes says it should be .55!) the TPS has to be tilted in such a way that it almost points up at a 45 degree angle, and is out of the tilting range of the two rainbow shaped slots. Whats this about the throttle minimum air plate though, I am intrigued?

 

The minimum air rate is the lowest RPM the engine will idle at if IAC is commanded closed. The throttle plate angle or gap between the throttle plate and the throttle housing is the minimum air the engine can receive if the IAC is fully closed with no vacuum leaks. This is adjusted in drive with an automatic. I believe the spec is @ 500(D) possibly 450. Once the thottle angle is set, then the TPS can be adjusted to coincide with the throttle plate. Not the throttle plate to the TPS. Some people set the throttle plate by watching the IAC counts. Set to about 25 or so. That gives it room to go up and down. If the IAC counts are at zero, the IAC is fully closed and at minimin RPM with the computer trying to lower the RPM, to the programed speed, due to too high an RPM (too much air). If the IAC counts are above 50, the IAC is opening farther than needed, which could mean the throttle plate is closed too far causing the computer to command more counts to keep the RPM at the programed speed (not enough air). Or throttle plate may be dirty.

 

.... I have no idea how to set what you just said ... I realize what you mean by minimum air rate, however how to set it seems a fair bit more complex... and i'm not entirely clear on what you mean by 500 (rpms?) or other numbers... thanks for good info though, could you clarify a bit?

 

Yeah I made a mistake, I meant .555. wouldnt the idle screw be the minimum throttle plate, i believe.

 

RPM = revolutions per minute, directly related to the Tachometer reading (engine speed).

That screw against the throttle lever is the throttle plate screw adjustment, not the idle speed adjustment. The computer controls the idle speed with the Idle Air Control Motor (IAC). Let's say the computer is calibrated for a 700 RPM idle speed. With the throttle plate set correctly, the IAC motor controls the idle speed and the TAC reads 700 RPM's. When you put the car in gear it creates a load on the engine and the computer sees the drop in RPM and increases the IAC counts, which in turn, opens the IAC motor until 700 RPM's is read. Then you turn on the A/C and create another load, and the computer increases the counts until the 700 RPM is read. You put the car in park, turn off the A/C and the RPM's increase and the computer drops the counts to lower the RPM back to 700. This is the basic operation of the IAC motor, to maintain a constant RPM. If you close the throttle plate and block off all air to the intake, the IAC would have to open a lot, more than necessary and sometimes fully open, to control the idle. In most cases the idle speed would be very noticeably real high and won't come down. The same if the throttle plate is set too far open, where the IAC all the way closed wouldn't be able to drop the RPM to the desired level. Rule of thumb is no more than 50 counts (read with a scanner in the data steam of the computer). If the IAC counts are over 50, the throttle plate is closed too far, usually due to vibration over time, if no one has messed with the plate screw. Most common reason for the throttle plate screw being out of adjustment is inexperienced "mechanics". All GM engines with IAC motors have a "minimun air rate" spec. Not to be confused with carbureted idle speed control motors, which push on the throttle linkage. So, with all air cut off to the engine (IAC fully closed), other than the PCV system, the engine has a lowest idle setting. For automatic trans vehicles, the spec is in "Drive". That air is entered into the intake from the throttle plate gap around the butterfly. The more the gap, more air, the higher the RPM. The smaller the gap, less air, the lower the RPM. You would adjust the idle RPM with the plate screw and the IAC fully closed to the spec. Once the plate is adjusted, the IAC would control the idle speed the way it was designed to. Once the plate screw is set, the TPS voltage would be set. Kind of like setting the points dwell angle, then the timing. Because setting the timing first, and then the points, would cause the timing to go out of spec. The IAC air inlet is just in front of the butterfly. The air goes into the IAC, and then goes behind the butterfly for air control. By blocking off the IAC air inlet, or closing the IAC motor, you are able to adjust the thottle plate screw to the desired speed without the IAC motor trying to compensate for the air change. After adjustment is made, the idle speed will go real high because the computer during the IAC being closed has tried to open with full counts. The ignition switch would need to be cylced or the vehicle may need to be driven to reset the computer once the IAC air passage has been cleared. That in a nut shell is why the minimum air rate is a very important adjusment that most people are not educated about.

Does that help?

 

I know all that, i understand the functionality of the IAC valve and I definately know what an RPM is. However, the only thing I didn't understand was how you go about testing your minimum air rate. I was just asking how to go about reading IAC cycles in particular, I need a scanner. I don't have one.

 

You don't need a scanner. All you need to do is cutoff all air to the IAC inlet, put the trans in drive, and adjust the throttle plate screw to approx 450 to 500 RPM's. DONE. Then adjust the TPS voltage to .55, DONE. If you can't adjust the TPS voltage you have another problem, either in the TPS itself, or the contact surface of the actuator arm on the back of the TPS or throttle linkage. May not be installed correctly. If the IAC is working, the computer will take it from there. Engine RPM when cold should be around 1000 RPM's and slowly come down. Engine idle when warm in park/neutral should be around 600 to 700 RPM's constant depending on the computer program. When the trans is put in drive, the RPM should adjust up to where it was in park. If that's the way it's working your done. If it doesn't then your IAC is not controlling the idle speed like it should, hence, the IAC problem breakdown.

Does that help?