Can you drive the car like normal without the IAC hooked up, right now it's causing my car to idle at 2000rpm. the IAC is new and the old one wasn't bad either I just thought I would make sure by buying a new one

 

would this be a sign of a bad PROM? even after i close the IAC and take out the ALDL jumper pin and set the base idle at 900 so I can drive it like normal, the idle will bog down after a couple minutes a start jumping up and down with the IAC unplugged.

 

On 87? Minimum TPI air rate is 450, why did you set it to 900, and what procedure did you use?

 

i agree.
something is wrong with what you did.
check your TPS too.

 

I know I didn't do the procedure right, I did the procedure correct the first 3 times and I was having a problem with the IAC opening up fully and the engine running at 2000 rpm.

I was just simply wondering if I could make the car drivable by closing the IAC, unplugging the IAC, and setting the base idle to 900 (what the IAC is suppose to govern idle to), so I would be able to drive the car a 20 mile commute to my shop.

But the car doesn't even want to idle setting it that way. It will idle great at 900rpm for about 1 minute then it dies to 600 and bounces up to 1000 and back and forth a couple times before dying. (this is without the IAC plugged in)

I replaced the ECM, so I am now thinking it's a bad PROM?

 

I used this method to set it.

https://www.thirdgen.org/tpimod2

 

That doesn't work for me unless I disconnect the "Set Timing Connector" first which is in the Alldata GM procedure for my car. Makes sense to me ECM will change timing when you adjust the idle which affects timing which affects idle rpm.

Have you disconnected the MAF and see how it idles?

 

question, that article isnt very exact on all the procedures, when it says to put the paper clip in the pins or whatever, do you turn on the car with the paperclip still in? or do u take it out after you disconnect the iac connector?

 

I start the car with the paper clip still in. then after I set it, I shut off the car, pull the paper clip and plug the IAC back in, and then I start it again.

no I haven't disconnected the MAF to see how it idles. MAF is new, new burn-off relay, new MAF power relay, and now I just replaced the ECM, all tryingto fix a previous problem that was occuring on the highway. now i'm having this problem.

I got another question. Is the TPS suppose to go from +.54v down voltage and then into the negative voltage as you turn the throttle? It's a brand new TPS.

 

...would that fry my new ECM?

 

no, it goes up. you must have it in upside down or you have your volts backwards.
does it go:
+0.54
+0.1
0
-0.1
-2...
-4...

?


if so, then thats weird.

if it starts at -.54 then goes more negative to -4.... then you are ok and have the polarity wrong

 

i left the paperclip in and nothing happened.
the reason you remove it is to prevent static electricity or voltage spikes from getting to the ECM, but i forgot and did it with the paper clip in and mine is a-ok

 

Well you might want to read the instructions that came with the new IAC valve. Usually at the end somewhere it will say that in some cases they will idle at like 2k rpms because theyve just been installed and the comp dosnt really know where it is (open closed where inbetween) so to remedy this i believe the directions say something like by driving it up at like 40 mph it will reset itself to its "home" position and be fine.

 

that's exactly what it does, but it goes to -5.99v haha. I'll change the new one back out with my old TPS.

I set it at +.54v because that same "instructions" link I posted before said anything .54+/-.075 is fine at idle. so I figured it was suppose to go from positive to negative. ****, who the **** authorized that ****?!?

 

put my car into "drive" with the engine at 2000 rpm? I don't think so, I wouldn't even be able to sit stopped.

 

Well clearly i know it dosnt sound the best but the problem is the comp just dosnt know where the stepper motor is ever pulse it steps the IAC valve but the comp kinda keeps track of the step count but when you install a new one who knows what step its at beacuse the computer certantly dosnt and its not like 3 steps there alot of steps. Even in the directions it says take it up to like 40 and it resets the count fixing the problem. As always its your car but unless you have another way of setting it ide say you dont have a whole lot of options. Although like i said if you dont believe me you can read the directions it will tell you the same thing. You will not tear your car up by driveing it a short distance taking it up to 40 mph but if someone else has a better suggestion go for it.

 

Once the "MInimum Air Rate" procedure is performed the ECM knows exactly where the IAC pintle is positioned.

It's no different than setting the initial timing, you set it at 6° BDTC because that's what's in the EPROM. That's it's reference point. If you set the initial timing at 8° all the EPROM timing maps will be off by 2°.
Once you reconnect the IAC and reconnect the Set Timing Connector and start the engine it may surge, but should immediately attempt to idle at the requested rpm which is dependent on temp, load, etc.
if it still idles too high something else is wrong.

What I grew up knowing as a gas pedal is no longer, the correct name for it is "Air Pedal," but more appropriate is "Accelerator Pedal", there's no need to step on the pedal when starting the engine that only confuses the ECM.

Idle speed is speed controlled by the ECM through the Idle Speed Control motor and is not adjustable, unless you have the equipment to reprogram the EPROM.

The minimum air rate is adjustable as follows:

1. Warm engine to normal operating temperature.
2. Turn off engine
3. Disconnect the distributor "set timing connector."
4. Ground diagnostic terminal
   • turn ignition on
   • do not start engine.
5. Wait 45 seconds for IAC to fully seat (Completely closed is the reference point)
   • then with ignition still on
   • disconnect IAC connector
6. Start engine
   • allow engine to go into "Closed Loop". See Note
   • Remove ground from diagnostic terminal.
   • Adjust idle speed to specifications using throttle stop screw (all air is now only going through the TB)
7. Turn ignition off
   • reconnect IAC connector
   • Reconnect the distributor "set timing connector."
8. Adjust TPS voltage if necessary: With ignition "ON" use a scan tool or 3 jumper wires to adjust TPS sensor to correct voltage specification. Tighten screws, then recheck reading to insure adjustment has not changed. (As for your new TPS, anything is possible, but it's more likely you have the leads crossed.)
   
9. Start engine and check for proper idle operation.

NOTE:When the test terminal is grounded with the engine running, it will cause the ECM to enter the Field Service Mode (FSM). In this mode, the service engine soon will indicate whether the system is in open or closed loop operation. In open loop, the light will flash 2-1/2 times per second; in closed loop, the light will stay out most of the time if the system is too rich.

My block is anything, but stock, a 388, the TB is stock, but custom bored to 52mm, if anybody should expected to have trouble with idle it would be me.
At startup it's 1200, but immediately settles down to whatever is requested for the conditions at that time, but that was after repairs to intake & exhaust leaks, bad fuel pump, and bad coolant temp sensor, and some reprogramming.

 

one thing,
when i was checking my tps voltage, i got .55 at idle and just below 4v at WOT. do i need a new one?
i am pretty sure i was getting WOT, but i guess that would be the next check
seems like my range was from .55 to 3.8 or whatever.. it was close to 4 but not over it like the directions said it should be

 

whats the diagnostic terminal?

 

It's a ALDL connector under dash left of center console; Assembly Line Diagnostic, and or Data Link. When the Check Engine Light is turn on by a trouble code it's used to communicate with the ECM to read the codes and serial data among other things.

You may what to check to see if the TV cable (transmission valve) cable isn't keeping the throttle from opening completely in turn minimizing the the TPS voltage.

 

I got the idle back to normal but I still have a problem. When I start the car, it starts up like a normal car and the rpm drops, after it sits for 1 minute or drive it for 1 minute it idles like it isn't firing on atleast 2 cylinders, even when cruising in gear. As soon as I floor it, instantly everything is fine and I have all the power but as soon as I let off it cuts out then goes back to misfiring. If I shut off the car then restart it the problem goes away and comes back in about 30 seconds.

My timing is advanced to 10*, someone already told me to put it back to 6* and I will before testing it again. But I don't think timing would cause this problem?

 

I've replaced everything that I can think of besides the PROM, so could it be going into closed loop after 1 minute? I have a heated O2 sensor. and once in closed loop would a bad PROM cause that? I'm not getting any DTC's