First off, this is not my car. It's a friends Firebird. 1988, 5.7L TPI (I think) It's a Formula body, if that makes any difference to the typical engines. Anyhow, he's been having trouble with the car overheating in parking lots and at stop lights. I followed through all of the troubleshooting available here and finally figured it out just when I was about to replace the CTS.

When he first popped the hood, the first thing I noticed was a fusible link that had melted in half. My friend thought that was something he did when he first got the car. He had removed a car alarm that didn't work anyhow and trimmed some wires and just left them hanging.

After all my troubleshooting, I finally found an image that included a fusible link and direct connection from the fan relay to the battery. It just clicked then. I patched the wire and now the fans work.

We took it for a test drive and it ran perfectly! When we went to start it 4 hours ago, however, it would start only if I gave it gas. Jon said it's done that before and he normally just puts something in the throttle body to keep it from dieing. After about 20 mins it usually runs fine again. The guy he bought it from told him something was dirty and needed to be cleaned out. Jon's not a car guy and doesn't remember what it was exactly.

The car has run fine for the last 4 months, up until it started to overheat, he didn't have any complaints. I don't understand why fixing the fans would screw up the idle. I'm tempted to adjust the set-screw for the idle baseline on the throttle body, but the car ran fine before and shouldn't need that adjustment. It runs smoothly as long as I give it gas. It's an automatic transmission and I drove it for 25 mins tonight without taking my foot from the gas. Any time I let up on the gas, it would die when the rpms dropped below 400.

Jon said if the trick with the throttle doesn't work, there was "Something about resetting a computer" and he unhooks the battery for a few minutes. We tried that tonight before I took it for a 25 min drive. I've read on here that the computer needs to relearn the idle settings after that, but shouldn't a 25 min drive be enough time to do so?

I did the paperclip thing and it just gave me 12 over and over again. I'm sorry if there's a former post that deals with this, but I've been looking for over 3 hours and the suggestions here haven't solved the problem yet. Could the TPS be to blame? I haven't taken a reading from it yet. Is that done from one of the leads to ground, or across the leads?

Thanks for all your help guys,
Jon (Yes, my friend and I are both named Jon)

 

hey buddy one night my car did the same thing to me would start, but wouldn't idle without gas, but when it warmed up it would idle usually but roughly. It turned out i had not plugged my IAC in all the way and the harness had come out and thats why she wouldn't idle. The previous owner was probably talking about cleaning the IAC because that can sometimes help out rather than replacing it. The IAC is (when looking at the engine from iin front of the car) on the left of the throttle body, below the TPS, i took it out and cleaned it off with carb cleaner, thats all i've got im no car genious but thats been my expereince

Josh

 

having the same problem with the 91 Z28 that i have resting out in my back yard.......was told that the egr valve sticks in the open position and this causes it to die.....unfortunately, it involves removing the intake to change it.....this is what i have come across....

 

Can you explain this a little more b/c when my car is in open loop for about 1-2 min. the car will not have a steady idle it will just die unless you give it gas. I def have the IAC plugged in all the way do you think from your experiance with this problem that I might need a new IAC motor? I took it out and cleaned the passages. maybe i did this wrong? I am getting really frustrated with this problem. Also when you did the IAC did it fix the rough idle? Thanks Dennis

 

The idle is controlled by the ECM with input from sensors.
For the ECM to properly control the idle, the minimum air setting, and TPS must be in spec.
Do the minimum air adjustment first, then the TPS.

Search for minimum air to find the procedure.

Adusting the idle screw changes the voltage output of the TPS which only serves to confuse the ECM.

 

im not sure if the IAC is necassary, and im not sure if its the only problem, but it could be, let me try to explain my situation. I got into my car after doing the thermostat, and having to remove the throttle body. I parked it at my gf's house, and got ready to leave a few hours later, on a cold night, maybe 30-35 degrees out. The car turned over great caught, and IMMEDIATLY died. did the same tihing a few times in a row, held the gas down a little, cranked it and it started and ran fine @ ~1200-1500 rpms. let off the gas it idled down..all the way to 0(read it died again) Started it with the gas, let itm warm up, drove it home, ran ok it seemed not needing any gas at stoplights or anything. After trying to figure out what the hell i could have messed up doing a simple thermo swap, i noticed the IAC harness was loose, not completely off, but loose. So a problem like yours in my opinion could easily be related to the IAC. May want to try a junk yard, they are easy enough to swap out, rather than a new one at a parts store. Otherwise try what others mentioned about the tps.

Hope you at least understand my story and can figure out if it still relates to you.

Josh

 

That is exactly how my car acts, there arent many junkyards in NY but I think that the IAC is about $50 but not sure so maybe I will go out and buy one. I bought this car while it was running bad and have gotten so far with it, now this is my last problem. for the time being. When I cleaned it I took off the throttle body, Is there a way to take it off w/o removing the TB? Thanks, Dennis

 

yeah it comes out with the throttle body on, kinda tight, i removed it awhile ago to clean it, i was just gentle with a big pair of channel locks, cleaned it with some carb cleaner

 

Try a new IAC it would be worth it if it's old. Also check for any vaccum leaks.

 

Thanks a bunch guys!

I can't tell you how elated Jon was when I put the IAC in and it ran! Of course that was after cleaning with fuel injector cleaner and then scraping the crap off the pintle.

Case solved!

Jon (2)

 

I would still do the Minimum Air Rate & TPS idle voltage procedures.
This is the procedure I use on my 88'.
Idle speed is speed controlled by the ECM through the Idle Speed Control motor and is not adjustable. The minimum air rate is adjustable as follows:
I first remove the IAC and push the pintle into the IAC motor until it's about 1/2" long, and reinstall it.
Best results obtained when TB is clean.

1. Ground diagnostic terminal, turn ignition on, but do not start engine.
2. Wait 45 seconds for IAC to fully seat (no air should enter through IAC passage if the pintle is fully seated,) then with ignition still on disconnect IAC connector (all air will now enter only through the TB otherwise base idle can't be set, just like the base timing can't be set with the set timing connector connected.)
3. Disconnect the distributor set timing connector ( if not the ECM will try to adjust the timing which changes the idle.)
4. Start engine and allow engine to go into "Closed Loop". (When Temp gauge stablizes if you don't have a scanner. I'm not sure, but I think the SES flashing light will increase, or decrease in frequency when the engine goes into closed loop because the diagnostic terminal is grounded.)
5. Remove ground from diagnostic terminal.
6. Adjust idle speed to specifications using throttle stop screw (scanner will give a more accurate rpm reading than a stock gauge.)
7. Turn ignition off and reconnect IAC connector.
8. Adjust TPS voltage if necessary: With ignition "ON/Engine OFF" use a scan tool or a jumper adapter to adjust TPS sensor to correct voltage specification. Tighten screws, then recheck reading to insure adjustment has not changed.
9. Start engine and check for proper idle operation.
10. Don't forget to reconnect the "Distributor Set Timing Connector"

Try to achieve the highest voltage reading at WOT (minumum of 4.50v) without losing the idle voltage setting (0.54v ±0.04v,) and watch the voltage reading as you slowly open the throttle, any sudden, and large voltage jumps are symptoms of a bad TPS.

 

my only problem is, I have a scanner but whenever i hook it up the rpms jump to about 1100 and the int and blm #'s are high. when i disconnect the scanner the rpms drop why this happens i dont know.

 

good to hear it was the issue, glad i piped up for once

Josh

 

RGarcia, do you do the minimum air set with the car cold, or after it's been warmed up?

 

If it will idle on it's own, do it after it's gone into closed loop.