I need some directions here. I've been trying to adjust the idle on my '87 Firebird, but it's always coming out about the same-too high.
The idle is about 700-800 rpm, and I'd like a very low idle, about 500 rpm tops.
Should I just pull the idle adjuster cable? Will that work? Or do I have to reprogram the prom?
Suggesstions anyone?

 

To adjust the minimum idle speed on your motor, you first have to put a paper clip in between terminals A & B on your aldl connector inside the car. Then turn your key on for about 30 seconds to let the IAC valve extend all the way. Then unplug your IAC valve connector. Let the motor warm up for a little bit and then you can adjust the screw on the throttle body that controls the idle. It may have a cap over the screw that you have to knock out. Just adjust from there to where you want it set to.

 

Hello Chieftain_57!!

Just curious as to why you'd want your idle speed set that low!!!!

 

An '87 TPI curb idle speed is controlled solely by the ECM and IAC working together. You would have to program the target idle RPM to the value you desire.

Of course, you CAN disconnect the IAC and try adjusting the throttle minimum air position stop screw to get the desired idle, but there will be several detrimental effects resulting from that.

 

Thank you for your answers.
85Iroc-Z, I've tried that, but it seems that as Vader says, idle speed is controlled by the ECM, and this is what I regard as way too high.
I didn't like the idle in the Trans Am the engine was in when I bought it, and now (here's the answer to your question 87IROC-DAN61) that the engine is in a 1957 Pontiac, the idle sounds really weird.
And I just love super slow idle!
The idle is the one thing I'd like to reprogram on my ECM prom...

What would the "several detrimental effects" be resulting from disconnecting the IAC?

Come to think about it: Where does the IAC draw its air? Maybe plugging the air supply would be a way to disable the IAC without getting a SES light?

 

the main effect to unplugging the iac will be constant stalling.
it will stall when starting cold, shifting into gear, at speed when you let off the gas,
at idle in gear, if you have ac it will stall when the ac pump comes on, etc.
just all the time.
it draws air from just in front of the throttle plates in the throttle body.

 

Yes, ATOMIC, I've read about she stalling problem... Do you have any suggestions as to how I'd be able to make the engine idle real slow? Is there any other way than burning a new chip?
I'll experiment some with the IAC disconnected, maybe it'll work as fine as a carb, which also has fixed idle. Can't hurt to try..?

 

I'm having a similar problem... but i did reprogram my prom.. it still idles too high.. also.. i can't pull out the minimum air screw anymore the throttle blades are closed all the way, my ecm seems to enjoy advancing the timing too much, if i unplug the wire for the Dist it'll idle correctly for a few stops but then it'll advancing the timing again and raise the idle...

 

nope, a new chip with a lower target idle is the only reliable way to do it.
may still have stalling issues with the idle that low, depends on how well the engine is balanced and how much the flywheel weighs (more=smoother)

 

the throttle plates shouldn't be closed all the way,
you will ruin the TB quick, it wears a groove in the bore and sticks.

 

Hello Chieftain_57!!

I gotcha!!

One of the effects of a super low idle is lack of proper oiling due to lower oil pressure at the super low idle setting!!



Sounds detrimental to me!!

 

After experimenting a bit I can now state that idle without the IAC connected is no problem, except when the engine is cold, and a few seconds after firing the engine up, even hot, when the accelerator has to be depressed a fraction of an onch. No stalling, no problem when coasting to a stop or anything.
And the idle is steady and nice at some 400 rpm. Just as with any carbureted car, the idle drops some when drive is engaged, but that's no problem.

And about the detrimentals. You may want more power, and you pay with poorer fuel mileage and a shorter life span on the engine and transmission. You want your car lower, you pay with less practicality and often a poorer ride. Etcetera.
You want your idle low, and you pay with low oil pressure.
You want something, you have to pay, simple as that

 

A healthy Chevy V8 can maintain sufficient oil pressure at 500rpm. Several full size sedans during the 70s ran idle speeds of 550rpm. I understand wanting low idle speed with an automatic transmission.

 

Hello Chieftain_57!!

I guess that you don't have an SES light in this 57 Pontiac either!!!



With the IAC disconnected, does the ECM go into "closed loop" mode, does it set any codes, and/or does it go into "limp home" mode???

 

Most vehicles will set a DTC if the ECM is unable to acheive desired idle. I have never seen any such code on an OBD1 GM.

 

******* No4, Have you tyied connecting a scan tool to look at data for desired idle and a possible cause of your idle problem? If your PROM was rewritten, your desired idle should differ from OE. Look at TPS and other possible causes.

 

as 87 iroc dan said closed or open loop when the ecm reports a un nominal temperature voltage or certain parameters or intervals of less than required run time the engine will of course give you a inconsistant idle, if you have a tpi in that old of a car why did you not go with a engine management set up like a pro jection system at that time you can set all the parameters you need and save yourself time playing with the oldschool prom junk it gets a bit hairy when you start playing with voltage, idle and other settings with the oem or modified prom it becomes a royal pain in the rear... old saying you gotta pay for performance...

 

Nice, ASE doc, to get a response from somebody understanding a benefit of low idle :-) The most important benefit of low idle in my case is that I like it, and it sounds plain wrong with a high idle on a fifties car.
I'm pretty sure the prom is original, as the rest of the car and engine was, and everybody hereabouts are afraid of injection systems, they're like woodoo...
87IROC-DAN61, I must prove you wrong, as I really have an SES light in my '57. In diagnostic mode it shows that the engine is working closed loop. Even without the IAC connected.


Apparently the IAC is working just fine, closing up when it should, and opening up as the ECM commands it to. The throttlebody works ok too, I can get a very low idle, or stall the engine by turning the air adjustment screw.
Can I reprogram my prom for lower idle, and if that's the case, can anyone steer me in the right direction?
I don't have any equipment, but I could get some if I'd know where to start.

 

Options for reprogramming desired idle in the ECM depends on what ECM you have. I don't know all the numbers by memory but they vary from the earliest the the latest. the earliest MAF ECMs used a basic PROM(programmable read only memory), which was hard programmed and could not be rewritten. To change any parameter in this type of PROM, you need to have a new one "burned". The later ECMs used an EPROM(erasable programmable read only memory) which could be programmed but only once, then it would have to be replaced in order to change programming.

Finally, and I don't remember if any 3rd gen received this type of ECM from the factory, GM started using the EEPROM(erasable erasable programmable read only memory) and did away with the replacable PROM. The EEPROM can be programmed using a J2534 pass through, almost while you drive.

Zaar mentioned using an aftermarket DFI system to manage the TPI. I use an ACCEL DFI system in my IROC Beast because I wanted to be able to tailor fuel and spark maps to fit my extreme engine and don't trust PROM "burners" do my programming for me. I really like the system and it allows me to make programming changes should I change anything in the engine. It also allows me to set idle wherever I choose. Of course, with this engine, low idle isn't an option. It does idle quite well though at 850rpm.

You might consider something like this for your application. The newer systems are really advanced and basically program themselves using wideband 02 sensors.

 

Thank you ASE doc for your input.
My ECM is an original '87 Firebird MAF systen ECM. It has the "hard programmed" PROM. I've read somewhere how you can burn new ones, and might be interested in trying. I remember reading that investments will be one or two hundred bucks to get started, so maybe an aftermarket DFI system would be a good alternative anyway?

For now my engine works perfectly, apart from requiring a bit of throttle when cold. Just as any old carb setup with the choke butterflies removed, as they often are anyway :-)

 

The aftermarket systems are pretty neat. they use the wideband O2 which most of the OEs still aren't using even today because of cost. The wide band allows the ECM to accurately monitor AFR thoughout the engine's entire operating range. This gives the ECM the ability to custom tailor its own fuel maps as you drive. I've spent hours upon hours tuning my ACCEL DFI and now that I've got a wideband AFR meter, I'll be doing more. All this could have been avoided if the wideband ECM had been available when I built my car. I remember my dad's 57 SuperChief what a cool old car! Have fun with that beauty.

 

Of course it would be nice to go Digital and have a new crate engine with all the bells and whistles. This is my first try at fuel injection, and this has been a very interesting winter with a lot of studying.
A huge satisfaction was felt as the PFI mill started on the first try!
Also, I'm on a budget, and after selling off the Trans Am body the complete engine with electrics and ECM, the TH700 tranny and part of the brake system cost me less than $1000.
Any way I like this car very much, I think its a keeper, so the future will tell if I'm going to invest in DFI. It's certainly possible!
Here's a pic from one of the first outings a couple days ago:



My Pontiac project home page can be seen here: http://www.waasadata.com/pontiac

 

Hello Chieftain_57!!

Nice set up, SES light to boot!!!

 

Thank you, 87IROC-DAN61!
It works a charm too! I've added a switch between A and B terminals on the ALDL connector, so I don't need a paper clip to check the codes, and to check if the engine runs open or closed loop.
Now I have a new "problem". I need to have the TCC (lock up) work in fouth only...

 

Stand alone TCC controllers are available. What is the problem with your current setup?

 

Immediately when second gear engages, the TCC locks up. Feels weird, and then third gear "clunks" in. I have disconnected the TCC wire, and now the shifts are smooth and nice, but of course the TCC is disabled.
I've seen a diagram somewhere, för connecting the TCC so that it works only in fourth, and I thinkt that would be a good idea for my setup.
For now, the original GM ECM does the locking up.

 

Hmm, this is strange. Factory TCC logic only allows for lockup in 3rd or 4th gears, above 45mph. Do you have the VSS circuit connected to anything? This should be setting a trouble code.

 

Hello Chieftain_57!!

I like the idea of the switch between A and B!!

 

The ECM uses the signal form the TCC pressure switch in the trans to activate the TCC solenoid. Also, the TCC solenoid is a vent type solenoid, meaning that it vents pressure from the TCC clutch to hold off engagement. If the solenoid is restricted, the TCC will activate with line pressure. Remove the trans pan and check these things out. Also, carefully inspect the harness inside the trans for any sign of rub though or other shorting.

 

actually i have a UVC light (erases the Eprom in 5 min) and the Q3 programmer, i've been using tuner pro(checked with WinALDL), found some issues with 870 DEF and ADX files on the TP website but moates website has revised versions that are correct, regardless, I didn't change the factory idle settings the Prom that was in the car when i bought it wasn't on a stock tune I changed it to the stock tune (from moates website as well) then added a few degrees of timing and took out some low load fuel,

the only thing i can't change is the idle, regardless of what i set the target idle to it will go up to 1000 in D and 1500 in P and it does this ALL the time open or closed loop with ought an SES, also from your suggestion i set the throttle plates to where they are happy, just before they'll stick again no change in idle, my IAC is at 80 steps aside from when i'm cranking its at 145 steps, but when i'm cruising it will go down to as low as 20 steps so the iac can go lower than 80, my timing will go to ~15 degrees advance which is fine when i'm driving but not necessary when i'm idling aparently

 

Strange that the TCC should be able to engage in 3rd and 4th only... Maybe there can be several different programs in these old chips?
I have disconnected the TCC from the transmission, and the shifting has improved immensely. Smooth, nice up shifts, but of course the TCC is not working at all. I guess this means that the tranny/TCC works as it should. I used a switch to engage the TCC on a previous car, and it worked ok, maybe I'll go that route this time also.
Here's how it was connected: