throttle position sensor..etc...

[bucket]

how does this effect performance..??:W

 

[toptechx6]

A great book that explains a lot about the systems in our cars, should be in every Vette owners library along with the correct Factrory Service Manual for your car.

Corvette Fuel Injection Electronic Engine Management 1982 Through 2001 : L83, L98, Lt1, Lt4, Ls1, Ls6, Zr-1 Charles O. Probst Paperback english 9780837608617 BENTLEY PUBLISHERS TRANSPORTATION BOOKS

 

[MBDiagMan]

TPS adjustment effects throttle response significantly, but unless WAY off, has little effect on overall power. There is power to be lost through misadjustment of the TPS, but there is little or no power to be GAINED by tweaking it.

 

[TedC]

Yes you can change throttle response by increasing the base voltage, but WOT performance remains the same. Don't go to high or you will see the engine light come on. I prefer using the stock specs. Verify 4.2+ volts at WOT with your foot on the gas pedal all the way to the floor. When I bought my 1988, it was showing only 3.9 volts. WOT performance improved when I adjusted it to post 4.4 volts.

 

[bucket]

thanx for the heads up..

 

[nelson84]

How exactly do you adjust it? I put a new one on my 85 vette and the car quit blowing smoke out of the exhaust the old sensor was hooped and it seemed to flood the engine some how. I just screwed it on and plugged it in. Now I read you are supose to adjust it;help.

 

[MBDiagMan]

How exactly do you adjust it? I put a new one on my 85 vette and the car quit blowing smoke out of the exhaust the old sensor was hooped and it seemed to flood the engine some how. I just screwed it on and plugged it in. Now I read you are supose to adjust it;help.

You just got lucky.

You properly adjust it using a digital DC Voltmeter connected to, as I recall the bottom two connections on the TPS. Look for .500 volts +/- about .04 Volts. To adjust, loosen the screws such that you can rotate it, but it is a little stiff so that it will stay in position once you get the correct reading. After tightening the screws retest the Voltage setting.

I haven't done it on one of these in a long time, but I think this is all correct. You can consult most any manual to verify my memory.

 

[TedC]

Two adjustment screws. I filed the TPS slots slightly so I had a little more adjustment voltage at WOT while keeping the base voltage at .54 volts. But a stock TPS should have no issue setting the base voltage properly and pulling 4+ volts at WOT. Don't assume you are all done by just setting the base at .54 volts. Verify WOT. You can use a VOM which is the low cost option and works just fine. A scanner is even better because it reflects what the ECM is actually seeing and you can measure inside the car. When I purchased my 1989, the idle (base) was set at .60 volts, and was way too responsive.

 

[MBDiagMan]

Actually, now days you can buy a pretty darn good Digital meter for $20 or less.

 

[Hib Halverson]

Once reason there are DMMs for 20 bucks or less is a lot of the units in that price range are POSes.

If you are buying a DMM for engine controls diagnostics make sure you get one with at least 10 meg ohm impeadance. DMMs with less than that will be inaccurate.

 

[TedC]

I've never had an issues when measuring voltages using a $10, $80, or $300 DVOM. Resistance accuracy is another story. As Hib points out, if you only have one DVOM, make sure it is at least 10 meg ohms. This is critical in testing circuit boards.

 

[MBDiagMan]

Yes, for many things a high input impedance meter is necessary and desirable, but for things such as the TPS adjustment, the cheapie from Sears will do fine. These are cheap enough, reliable enough and compact enough to throw in an emergency toolbox or in one of the compartments in the cargo area of a C4.

 

[joshwilson3]

Can you set this with it off the car, or does it need to be bolted to the car? And if the later, does the car need to be running?

I removed my TPS for cleaning on my 89, and forgot about it needing to be bolted back up a certain way.

 

[vetteboy86]

The TPS needs to be installed on the car. This is the main reason for adjusting it, because when you install it on the car idle position Voltage, and WOT position voltage may not be correct.

The car does not need to be running. You do need the key turned to ign.

 

[joshwilson3]

The TPS needs to be installed on the car. This is the main reason for adjusting it, because when you install it on the car idle position Voltage, and WOT position voltage may not be correct.

The car does not need to be running. You do need the key turned to ign.

I was able to find that article on setting the TPS and idle. I'll need to adjust my idle as it looks like the blades don't shut straight up and down. I noticed that block off plate for the screw that stops the blades has been removed.

And it looks like I'll need to get an adapter to check the TPS voltage. Though, in the article it told how to check for the base or idle TPS setting. But it didn't mention anything about the WOT setting. If you get it set for the base setting, but it doesn't get 4+ volts at WOT. How do you adjust it since you can only make one adjustment? Or does that mean the TPS is bad?

My IAC looks really clean on the needle. Though, I may still plug it back up to the car to get the needle to pop out anyways. I'm assuming to get the needle back in, you just stick it in and rock it back and forth very slowly? It's been a while since I've done an IAC cleaning.

 

[vetteboy86]

What RPM does your car idle at now? I wouldn't be adjusting the idle with the throttle screw. It's not like a car. You start turning that screw than you are fighting the computer that is trying to compensate by using input from the TPS and also varying the IAC steps.

I think I have read tech articles that say to set it at WOT then what it falls back to, just has to be it. Yes you are fighting to variables, and you need to do the best. The WOT setting i believe is more important, and it needs to be close to 4.5 volts.

 

[joshwilson3]

What RPM does your car idle at now? I wouldn't be adjusting the idle with the throttle screw. It's not like a car. You start turning that screw than you are fighting the computer that is trying to compensate by using input from the TPS and also varying the IAC steps.

I think I have read tech articles that say to set it at WOT then what it falls back to, just has to be it. Yes you are fighting to variables, and you need to do the best. The WOT setting i believe is more important, and it needs to be close to 4.5 volts.

I don't remember the idle speed. I've only driven it 4-5 times in the last 6+ months. I'll figure the idle out when I put everything back on the engine that I have off, and when I change the coolant.

Though, I think it idled at 700-750, but not sure. I know it is not a good idea to mess with the throttle screw. But the block off plate is missing, so the PO has already messed with it. I noticed the blades don't shut all the way. The blades are very slightly still open. I don't know if the blades are supposed to be like that, or straight up and down. I know there is a little square hole on top you can look in and see the top edge of one of the blades. I'm assuming that is there to tell you where the blade is stopping at.

 

[TedC]

Minimal air (yes the screw that some think is idle speed adjustment) should be checked before setting the TPS, especially if one feels it may not be right. Search under my name for the detailed steps. Properly set, the throttle plates (blades) do not close 100%, this is why it is called minimal air. The ECM is calibrated to adjust the IAC position based on a minimal air speed of around 450 rpm. I've had better luck with idle quality by replacing IACs than trying to clean them. Just make sure (new or old) that it is properly seated before installing. IACs come with different shapes, so make sure you match up if replacing. The throttle body has a year on it. I worked on a 1988 that someone had installed a 1986 throttle body using a 1988 IAC. Once we figured this out and installed a new 1986 IAC, it idled perfectly.

 

[Hib Halverson]

A great book that explains a lot about the systems in our cars, should be in every Vette owners library along with the correct Factrory Service Manual for your car.

Corvette Fuel Injection Electronic Engine Management 1982 Through 2001 : L83, L98, Lt1, Lt4, Ls1, Ls6, Zr-1 Charles O. Probst Paperback english 9780837608617 BENTLEY PUBLISHERS TRANSPORTATION BOOKS

I disagree.

I reviewed this book for the CAC right after it was printed. It's full of errors and inaccuracies.
Corvette Fuel Injection & Electronic Engine Control: 1982 through 2001 - Corvette Product Reviews

I agree with "toptech6" in that the Factory Service Manual is a good thing to have in a Vette related technical library, but the Probst Fuel Injection book is not worth even half of its cover price because of inaccuracies. If you're looking for books which explain electronic fuel injection there are many other better titles.

 

[joshwilson3]

Minimal air (yes the screw that some think is idle speed adjustment) should be checked before setting the TPS, especially if one feels it may not be right. Search under my name for the detailed steps. Properly set, the throttle plates (blades) do not close 100%, this is why it is called minimal air. The ECM is calibrated to adjust the IAC position based on a minimal air speed of around 450 rpm. I've had better luck with idle quality by replacing IACs than trying to clean them. Just make sure (new or old) that it is properly seated before installing. IACs come with different shapes, so make sure you match up if replacing. The throttle body has a year on it. I worked on a 1988 that someone had installed a 1986 throttle body using a 1988 IAC. Once we figured this out and installed a new 1986 IAC, it idled perfectly.

Thanks. I'll do that search and check the year of my throttle body. I was detailing the engine and plan on replacing the valve cover gaskets, and paint the valve covers. So, I figured I'd just pull and clean the throttle body while I had everything apart.

Got any tips on cleaning the throttle body and smog pump? Can't seem to get those clean like the plenum.

Oh, and here is a copy and paste of that article on adjusting the TPS. I have on order that TPS adapter that lets you hook up your multimeter. So, what screw is he talking about to adjust for the minimum idle speed? The screw for the minimum air?

How to Adjust your Early C4 TPS and Idle Speed
by Lars Grimsrud
SVE Automotive Restoration
Musclecar, Collector & Exotic Auto Repair & Restoration
Broomfield, CO Rev. New 6-15-00


This tech paper will discuss the procedure for correct adjustment of the Minimum Idle Speed and for adjustment of the Throttle Position Switch (TPS) on the early C4 Corvette TPI systems. These steps apply specifically to the 1985 model year, and in general to other years. Later model years do not have adjustable TPS's.
General


Idle speed and off-idle throttle response on the early TPI systems is determined by correct adjustment of the minimum idle speed screw combined with a correct setting of the TPS. I've seen many of these cars that have had their idle speed "corrected" by well-intentioned mechanics and owners by simply screwing the minimum idle speed screw in a few turns. This really messes up the settings, and will not make your car perform properly. Doing a correct setup of the TPS is one of the easiest ways to make your car feel and respond better. To maximize the benefit of this procedure, I recommend that you first remove your Throttle Body (TB), disassemble it (it's incredible easy - there are a total of about 5 pieces in it…), clean the TB up really good with some spray carb cleaner, and put it back together. A nice clean TB will really put an edge on the performance improvement you will get by doing this procedure.


The Service Manual has instructions for doing these operations, but the directions are scattered through several sections of the Manual. Here is the complete, step-by-step process for doing this (not including TB rebuild). All specs and steps are taken directly from the Manual (all 3 different sections), and this process is absolutely correct.


Tools & Equipment


You will need the following tools and equipment:


1. A set of Torx wrenches. You can buy a complete set in a nice, genuine plastic pouch at Sears.
2. A good digital voltmeter that will read voltages less than 1 volt.
3. A paper clip.
4. A small screwdriver.


Procedure


There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC). Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.


You will also be playing with the diagnostic connector under the dash. Remove the cover (if it's still in place). Bend your paper clip into a "U" shape. You will be playing with the two top right hand terminals ("A" and "B") in the connector.


First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It's located on the driver's side of the TB. Remove this plug if it's there.


With the IAC connected and the ignition "OFF," stick the paper clip into the diagnostic connector from "A" to "B." This grounds the diagnostic lead.
Turn the ignition to the "ON" position without starting the engine. Wait 30 seconds.
Now, with the ignition still in the "ON" position, disconnect the IAC connector at the IAC.


Remove the paper clip from the diagnostic connector.


Start the engine and allow it to reach normal operating temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.


If your car is an automatic, set the parking brake and put the transmission in "DRIVE." If your car is a manual, leave it in neutral.


Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.


Shut off the engine and re-connect the IAC.


That's it for idle speed. Now on to the TPS.


There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires. You can either buy a special harness connector that breaks these wires out (from Mid America), or gently pierce the insulation of the wires with the pointy prongs on your volt meter. You can also stick a paper clip into each of the two top locations of the connector and clamp onto the paper clips to measure the voltage. Whatever is easiest for you.


Turn the ignition to the "ON" position without starting the engine.
Loosen the TPS Torx adjustment screws.
Set your volt meter to a low scale DC volt setting that will accurately read less than 1 volt.
Measure the voltage between the two top TPS wires.
Adjust the TPS by rotating its position until you get a reading of .54 volts.
Tighten the Torx screws and recheck the voltage. Re-adjust if necessary to make sure voltage is right at .54.
Turn the ignition "OFF."

You are now in perfect adjustment on idle speed and TPS output. Start the engine. It may take a few seconds for the car to "catch on" to its new settings.
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