I have recently aquired a 92 Firebird V6.

260,XXX Miles, Regularly Maintained & Tuned Up (pro-long oil additive since 1994) ** All Highway Miles

The Vehicle Has Sat for 7 Months, Started weekly but undriven.

Last Tune-up Unknown...

1000RPM Idle After Warm Up (PRIOR TO ANY PART REPLACEMENT)

Begun a DIY tune-up, and have encountered idle issues after replaceing of the following components: Spark Plugs, Wires, Distributor Cap & Rotor

Findings: Old plugs very black, appeared worn. Underside of Cap revealed Corrosion And white build-up, Rotor Appeared Worn and Rusted. Underside of Rotor/Top of actual distributer Covered in Rust.

I replaced all parts indicated and metal brushed the rust off the distributer to best ability. I also noted a small 2" span of vaccum line above the cap was bad and was replaced. Intake cleaner was gone so havnt checked rest of vaccum lines yet.

Symptoms:
First Start, Idle raised to 1600 and continued to 2000RPM in park, failing to decline. Second Start, Idle raised only to 1500RPM and failed to decline.
-Placed vehicle in gear at this point, vehicle idle declines to 1000RPM
-Drove Vehicle and topped off gas with 92 octane, Gas was low for 7 months . (Alot of water had dripped from tailpipe's prior to all of these part replacements, possible gas tank condensation?)
-Drove very smooth under acceleration. WHEN AT A slow to complete stop after acceleration, The idle drops anywhere from 700-500 and bounces back up to 1000. Car did stall once, but it was on a very low tank exiting a steep hill onto flatland. (Before getting new gas)

Summary: Vehicle idle stays at 1500 untill placed into gear.(even after long waitng period) In any gear but park, 1000. Slow to stop Driving Idle drops to 500 and rises to 1000.

IAC (unchecked) TPS (unchecked) Entire Vaccum system (unchecked) Injectors (no cleaner treated, no ohm's checked) PCV Valve (unchecked) Fuel Filter (unreplaced) Timeing (unchecked)

Pretty sure Cat is shot, getting a rich funy smell as well as rusted metal flakes from exhaust. ALSO seeing water vapor on concrete under muffler tips.

Also experiance a light bubble or light popping sounds from exhaust note at high rpm 5000-6000 K (IN PARK ONLY) Sound undetected under acceleration. Sound was described to me as a very light backfire noise? Definitly not the loud explosion sound I normally associate with backfire.
I am a total NEWBIE to pontiac/gm, and have little to no access to data and electric reading tools. THANKS for your help, please be detailed.

 

Sounds like you're a newbie to cars in general reving the engine in park to 6,000. Do you really want to sling a rod out the side? Check the stuff you have listed as unchecked and change the fuel filter.

 

Usually any reving is done under neutral... Allthough this one time I was exhausted and I just did it in park... thank you for your advice as to not throw a rod... I will note that, and make sure it isnt done again.. but i must ask "Why it can throw a rod in park gear, and not in neutral?" or did you mean parked period?

checking other areas noted today... BUT can anyone else with similer problem experience list what fixed it? And anyone able to go over the excessive water vapor in my gas tank if it's effecting the idle? or ignition period.

 

water out of your tailpipe isnt abnormal

Reving a TPI? to 6k isnt a good idea, nor is it on any stock valvetrain for that matter ( ESPECIALLY WITH 260K!)

 

Update:

Replaced 90% if not 100% of all vaccum lines exposed in bay.

Removed and cleaned IAC. Spring pretty much popped right out without any turning. IAC pindle and spring compressed to 1 1/8" and stayed in that position... is this normal?

Major Black Gunk found on IAC & The tube the IAC is located in. Cleaned well, and Throttle body also cleaned out.

TPS sensor removed and cleaned and put back.

RESULTS: IDLE starts at 1500 rpm's and slowly declines to 1000rpm. Under acceleration the idle hesitates or drops down -200/-300 rpm from any position then properly accelerates. After acceleration the RPM's decline to 1500 and slowly decreases to 1000 then 700 and stays constant untill acceleration. Then cycle repeats. Cars Throws Engine Light When idle sticks on 1500, then light goes away when idle returns to 1000-700.

Friend physically pushed throttle cable plate when stuck at 1500 and idle intermittenly would return to 1000-700 RPM

What you guys think? going to replace tps and iac... anything else I should look into?

(car was never reved to 6000rpm that was my mistake of what the redline was ...actual revs never exceded 5000)

 

Do you have a volt meter so you can check the TPS voltage? Do a search on what wires to tap into and voltages you should be seeing. As far as the reving, don't rev so high with no load on the engine.

 

I would try and pull the code and see what it is. That will give you some direction. It could be a very sticky IAC. The code for that would be a code 35.

Q: How can I display the error codes from a Service Engine Light?
A: If your car does not have the 12 pin DLC connector, you may not be able to manually "flash" your trouble codes. The language "may be possible" appears to suggest that this method should work with most, if not all, 12 pin DLC equipped cars.
THE CONNECTOR
----------------------- | 1 2 3 4 5 6 | | 7 8 9 10 11 12 | -----------------------
DISPLAYING THE TROUBLE CODES
Run a wire/hairpin from Pin 6 to Pin 12 with the ignition off (although on later cars it should be from Pin 5 to Pin 6), then turning the ignition to the on position without starting the engine will flash the "Service Engine Soon" light in the following sequence: flash, pause, flash-flash, long pause flash, pause, flash-flash, long pause flash, pause, flash-flash, long pause Following this "12" code repeating three times will come any trouble codes stored, flashing each of them three times. If you do not see the "12" flash three times, your diagnostic circuit is defective. Some vehicles will display stored trouble codes, then "12" again, followed by energizing "most system controlled relays." The fuel pump relay will not energize. The idle air control valve will fully extend to enable checking minimum idle speed.
CLEARING THE TROUBLE CODES
Turn the keyswitch to the off position. To clear any trouble codes, disconnect the power feed for 30 seconds. If this is done at the battery, and your car stereo is equipped and programmed with a four digit pin code, you may have to re-enter that as well to use your stereo again. A better place to remove power is at the fuse.
TROUBLE CODES

12.No reference pulses to Electronic Control Module (ECM).
13.Oxygen sensor signal stays lean during warm engine cruise
14.High temperature indicated at engine coolant temp sensor
15.Low temperature indicated at engine coolant temp sensor
16.High battery voltage OR Direct inition system open or shorted to ground
17.RPM signal problem
18-20.N/A
21.High voltage at throttle positon sensor
22.Low voltage at throttle positon sensor OR Fuel cutoff relay circuit open or shorted to ground
23.Low temperature at manifold air temperature sensor OR Throttle position sensor error
24.Circuit fault in vehicle speed sensor
25.High temperature at manifold air temperature sensor OR Vacuum switching valve circuit open or shorted to ground OR High voltage at ATS sensor
26.Fault in quad driver module
27.Fault in 2nd gear switch
28.Fault in 3rd gear switch
29.Fault in 4th gear switch
30.N/A
31.Low voltage at manifold absolute pressure sensor OR Fuel injector OR Park or neutral switch OR CAM diagnostic OR Governor malfunction OR Wastegate overboost OR Wastegate eletrical signal open or shorted to ground
32.Fault in barometric pressure sensor circuit OR Fault in exhaust gas recirculation valve diagnostic switch OR Fault in electronic vacuum regulator valve
33.High voltage (low vacuum) at mass air flow sensor (or MAP sensor)
34.Low voltage (high vacuum) at mass air flow sensor (or MAP sensor)
35.Idle speed can not be set to desired RPM
36.Burn off at mass air flow sensor OR Problem in transmission shift OR Fault in direct ignition system OR Missing pulses in electronic spark timing signal
37.N/A
38.Fault in torque converter clutch brake switch
39.Fault in torque converter clutch circuit
40.N/A
41.Fault at cam sensor OR Cylinder select error OR Tach input error
42.Fault at electronic spark timing circuit OR Fault at direct ignition system OR Fault at fuel cutoff relay circuit
43.Low voltage at electronic spark timing circuit
44.Oxygen sensor lean
45.Oxygen sensor rich
46.Fault at vehicle anti-theft sytem OR Fault at power steering switch
47.Problem at Electronic Control Module (ECM)
48.Misfire
49.Vacuum leak
50.N/A
51.PROM error
52.Problem at Electronic Control Module (ECM) - Missing fuel calpac missing OR Analog to digital converter error OR Fault at quad driver module OR Low voltage at oil temperature sensor
53.High voltage at battery OR High voltage at exhaust gas recirculation valve OR Voltage reference error OR Problem at vehicle anti-theft system
54.Low voltage at fuel pump OR Low voltage at Fuel pump relay OR Output failure at quad driver module
55.Problem at Electronic Control Module (ECM) - ECM failure OR Serial bus error OR Fuel lean malfunction
56.Low coolant or corrosivity OR Fault in port throttle system vacuum sensor
57.N/A
58.Problem at vehicle anti-theft system
59-60.N/A
61.Oxygen sensor degraded OR Port throttle system error OR Cruise control problems
62.Gear switch input diagnostics OR High voltage at oil temperature sensor OR Fault in cruise control- vacuum solenoid circuit
63.High voltage at manifold absolute pressure sensor OR Fault in exhaust gas recirculation valve OR Fault at right oxygen sensor
64.Low voltage at manifold absolute pressure sensor OR Fault in exhaust gas recirculation valve OR Right oxygen sensor lean
65.Failure at exhaust gas recirculation valve OR Faulure at injector peak/hold diagnostic OR Right oxygen sensor rich OR Fault at cruise control position sensor
66.Internal reset of Electronic Control Module (ECM)
67.Fault at cruise control switch
68.Fault at cruise control switch
69.Fault at air conditioner pressure switch
70-87.N/A
88.Internal reset of Electronic Control Module (ECM)
| 1 2 3 4 5 6 |
| 7 8 9 10 11 12 |

 

IDLE ISSUE FINALLY RESOLVED

Replaced IAC and TPS sensor. No change is symptoms.

Friend came bye and noticed the TB was sticking. We removed the intake and gave the butterfly some extra cleaning feeling the sticky deposits rather then eyeballing them. A Good Second cleaning allowed the TB to fully close again.

HOWEVER the External rocking peice attached to the throttle cable had some side to side play. Is this normal? or should I look into replacement? Or self repair?

Idle is currently corrected.