I remember seeing 0.54 V when my mechanic set the TPS a while ago. I printed off the procedure but I think maybe he set it at 0.54 V @ normal idle, not the 450 RPM idle (we never could get it that low, must have missed something).

I am going to attempt to check it tomorrow when I buy a digital multi meter after setting base idle. I'm going to try for around a 0.62-0.65 V cuz I read that it will yield better performance and quicker throttle response.

A while back I did have a guy kind of tinker with my chip and I'm not positive all the settings were correct for it. WOuld adjusting my TPS voltage alter some paramater programmed in the chip?

Also, once I set the base idle at 450 RPM with IAC pintle fully extended and unplugged, do I turn engine off to read TPS voltage or must the engine be running to read voltage?

Tell me if this is right(I've read 2 diff sources, and both aren't exactly the same)

IAC
jumper A & B with paper clip
key on, car off.
let sit for a minute to extend IAC pintle
disconnect IAC power
start car and let get to operating temp
turn tb blades down by screw in back of tb until 450-500 rpm
turn car off
connect iac power
remove jumper pin
restart car


Now, to test the TPS voltage (want the 0.60-0.65 V @ 450 rpm right?)..Does the engine have to be running at 450 rpms for testing, or should it be off?

before plugging the iac power back in,
check tps voltage with dmm
adjust to 0.60-0.65 V
remove jumper
reconnect iac power
start car?

I've read a source that tells me to disconnect the timing connector (tan wire?) during the process. Also, the tech tip says to remove the paper clip from the diagnostic port before starting the engine to get it to 450 rpms, while 65z01's site says to remove the paper clip after the 450 rpm has been reached.
The tech tip doesn't say anything about the iac pintle being extended to test tps voltage while 65z01's site does.

I'll just try to do 65zo1's way, he seems to know what he's doing, :D

 

Thanks for the vote of confidence; I've picked up those performance tips and procedures from several books on TPI and tuning TPI.

I find that my TPS reading at normal idle (~600-700rpm) is around .73-.74 Vdc; if you get it a little too high the ECM will throw code 21 at idle.

The reason for adjusting TPS base idle voltage with the engine Off is that you also need to open the throttle fully to adjust the TPS to as close to 5Vdc as possible; I don't like to do that with the engine running. It's this combination of higher base idle reading and max WOT value that gives better throttle response. It's sort of like a cheap way to "reprogram the chip" so that the ECM sees more throttle advance and bumps fuel & timing.

You don't need to deal with the tan/blk wire unless setting base timing, which I would do after "tweaking" the TPS setting as that will increase timing advance as well as injector pulse width under hard acceleration.

I advance base timing until I just knock retard at high RPM at WOT; then back off a deg or so...just until there is no knock retard or maybe just a deg or so of retard. This seems to give best throttle response as well as pull at the low end with no power loss near the shift point(s).


[Modified by 65Z01, 4:25 AM 10/27/2003]

 

Also, there was a Tech Bulletin put out by Chevrolet some years back raising the idle speed recommendation to 550 RPMs as opposed to the 450 that is listed in the Service Manual.

Since my engine combination will not idle at anything close to 550 RPM, I set my TPS voltage just as the Service Manual says, with the ignition "On", engine off. I choose .61 which seems to work best for my combo. My PROM is burned for 850 RPM idle speed.

The Service Manual for the 86 does say - in bold print - not to forget to disconnect the EST wire when setting the minimum idle speed with the Throttle Body screw. Can't comment on other years tho.

As far as the jumper to ther ALDL A&B terminals, I've read it both ways. I choose to only connect and disconnect the jumper wire with the ignition "Off". I don't know if a voltage spike would result from connecting or disconnecting the jumper wire with the ignition "On", but I figure "Why chance it".

Jake

 

mine idles at 550 with .056 and seems to do well (87)