Having issues with idle when at operating temp about 15-20 mins of being started. I have run into lots of dead ends on this forum and not many responses to any post. I am running a 5.7 TPI system on an 87 camaro. All new sensors on vehicle and all new gaskets without any vaccum leaks. Need help finding out what is going on...Posting video on youtube view at about 20 secs into video and watch when I rev the engine and how the needle on rpms go down then up and then corrects its self.
http://www.youtube.com/watch?v=6F53guhqYNY

 

 

Bump..Bump

 

TTT

 

What is your Curb Idle (throttle stop screw) speed set at?
What is your TPS Voltage set to?

Your curb idle speed (IAC Disconnected) should be about 450-500 rpm, or at least 100 rpm less than your specified "normal" idle speed.. With the throttle stop properly adjusted, the TPS voltage should be set at .54 volts.

 

TPS is right on and the RPM's are high at 1400 with IAC unplugged. I tried to set the idle screw back on 58mm Holley Throttle and can not get the plates to go back anymore... Do you know if I need to mess with the spring on linkage?? Not sure how to get this down on RPMs....HELP Please! Anyone know about these Holley Throttles?

 

Ok used these instructions on setting TPS and RPM's and still is doing the same thing....Could it be the ECM/PROM when I unplug the brown wire for timing it runs really good.... Any ideas???

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.


Questions, Comments & Technical Assistance
If you
have questions or comments regarding this article, or if you notice any
errors that need to be corrected (which is quite possible since I’m
writing this from memory…), please feel free to drop me an e-mail.
Also, if you need any technical assistance or advice regarding this
process, or other maintenance issues, feel free to contact
me:

lars.grimsrud@lmco.com

and RPMS

 

Bump....

 

TTT

 

Did you do the "minimum idle speed" procedure? That is exactly what you need to do.

When you jump the A-B in the diagnostic terminal as described above, the IAC valve should "buzz". Did your IAC "buzz"? This is something that can be clearly heard. If you DID NOT hear the IAC make a noise when following those instructions, it is likely that the IAC is bad or jammed. If you screwed your IAC into the throttle body with the plunger extended, you could have jammed it or ruined it. You need to be sure that the IAC plunger is FULLY RETRACTED before you try to install the IAC.

Here is an old motorcycle trick you can use to check your throttle plate setting. you will need a .005 feeler gauge and a torx screwdriver for the idle screw. With the air intake boot off, screw the idle stop screw until it is NOT Touching the tab on the throttle arm. Open the throttle, insert the feeler gauge at the 6 o'clock of one of the blades, close the throttle (Gently). Now try to pull the gauge out, it should be held tight! If not then something is holding the throttles open, NOT GOOD. If the feeler gauge is not held by the throttle plates when the stop screw is turned out, then the throttles are not closing properly. The plates must close completely (the feeler gauge held tightly and cannot be removed) when the screw is backed all the way off. If it passes that test; screw the stop screw in until the feeler gauge can be easily inserted between the bottom of the throttle blade and the casting. With the feeler gauge in place, screw the stop screw OUT to close the plates and until the feeler gauge just has some resistance when pulled out. This will position the throttle plates slightly open. Does that make sense to you?

 

I did do the minumim idle procedure and brought the rpms down to 400 in drive. Is that the correct RPM's? Did not hear the IAC Buzz as the fans turn on so could not hear. All Relays,sensors,EGR and IAC have been replaced with quaility ACdelco products. The distrubitor/module and fuel injectors changed. Not sure if there is anything wrong with the plates on throttle as that is new too. I get what you are talking about and will check out. Appreciate the help just seem to be running into a dead end....and things left to check.

 

400 is close enough, in drive. I am thinking your problem is that the ECM is hunting for the right mixture. Maybe the O2 sensor is too cold or not working?

 

The O2 sensor was replaced too... I am think it has to be the ECM but just replaced with another used one and same issue. Think I might try a new ecm and maybe new prom. Keep the ideas coming! Thanks mlynch001 for being the only one to reply.

 

I do not think this is the ECM. Are you running Headers? My 85 El Camino had a little of this "idle surge" sometimes, still trying to work it out. I am using a 91 730 speed density ECM and F-body headers and the O2 sensor seems to be a little slow to respond. Speed Density systems seem to be more sensitive to this, but yours is not a SD system. Mine is worse on cold days, but not as much variation in idle as you have. Is you IAC valve cleaned really well? Is you MAF new or a "Known good" part? Is the PCV Valve and hose in good shape? Is the PCV Valve new? AND Is it the "correct" part for the vehicle? We are looking for the proverbial "Needle in a haystack"! This is going to turn out to be something REALLY Stupid or Simple!

 

Hello all,

I assume you replaced the original 1 wire oxygen sensor. I had a similar idle hunting problem and I would recommend upgrading the "quality AC-Delco 1-wire O2 Sensor" to a heated 3 or 4 wire sensor. The idea is that, at extended idle, the O2 doesn't get warm enough to operate properly. Wire in the new sensor via a relay and you should see an improvement in your idle.

Also if you have access to a scanner, you should take a look at the BLM, INT, and O2 values, this will let us see what the computer sees and look for obvious problems.

If you don't have a scanner do a search for WinALDL and build an ALDL cable to connect your car to your laptop. Sounds difficult but actually very easy.

Do you have the original injectors in your car? I wonder if your injectors are leaking causing a rich condition that the ecm can't recover from.

You mentioned a 58mm Holley throttle body. I had one of these HUGE throttle bodies on my car at the same time as the idle problem. The ecm and IAC could never get my idle low enough because even at minimun idle and no IAC counts, my car still would idle unevenly. Eventually I put the stock 48mm tb back on and now i have far fewer idle problem.

Check over all your vacuum lines. If you touch them and they leave your hands black, time to replace them.

Hope this helps.

 

Thank you skibum2100 sounds like good information given. The O2 was replaced can not remember what brand it was. I did replace the injectors with the Bosh III that everyone seems to recommend. Whats a 3 or 4 wire connection you speak of? Do they sell ALDL cables to connect to computer? And vacuum lines all replaced....Will try this stuff out and let you know if it worked. Again much appreciated for your ideas!

 

Cheers AJ,

Good...Bosch III's are good.

The "3 or 4 wire" refers to a newer heated O2 sensor from an LT1. I just bought an oxygen sensor for a 94 camaro (I think) and made sure that it had at least three wires (in my case 4 wires) attached to the oxygen sensor. In a 3 wire sensor: one wire is 12V for the ceramic heater, one wire is the ground for the ceramic heater, and the last wire is for the ecm. In a 4 wire: it is the same as above but you get an extra ground for the sensor to guarantee a good ground, instead of just relying on the ground through the manifold, into the engine.

Yes, they do sell ALDL cables already premade. The first google result was this...
http://www.aldlcable.com/

However I was able to assemble a cable with parts from Radio Shack for far less than they are charging. If you know how to use a soldering gun, then you can make it too.

 

Ok now I feel stupid I have a SNB block which is a 87 TPI engine but have TBI cylinder heads just checked the # is 14102193... TPI are set at 6BTDC and TBI engines are set at 0BTDC. Everyone check this out very easy fix but took me a lot of parts a money don't make the same mistake!! Thank you skibum2100 for trying!