Pilotrick50

iTrader: (1)

I just bought a parts car. 1989 Firebird Formula, 305 TPI, factory duel exhaust, 5 speed, 3.42 posi rear end. Ok, I have been reading as many of the threads dealing with the TPI prior to posting this. When I bought the car they were sick of working on it trying to get the problem with the TPI to idle so they took off the TPI and put on a 4bbl carb....They ran out of money and patience before finishing when I came along and bought the car. I have put the engine back to it's original state as I wanted a TPI engine and yes there is a problem of the engine not idling and stalls. I believe it is all dealing with the IAC. The car starts and revs to 2500 then drops and stalls. When I put the new IAC in I had it set at 1 1/16 inch, I did not plug it in, I then started the car and it Idled at 1500 and purred like it should. I let the car warm completely up then shut the car down to begin the process of setting the idle according to the thread I read in the tech forums. I plugged the IAC in and shut the car off. I did the paperclip jumper, waited 30 seconds then removed the paperclip and tried to start it. I could never get the car to start let alone idle. I took the IAC back out and set it at 1 1/16, reinstalled without plugging it back in and it starts and idles at 1500, I then plugged it in and the IAC closed and stalled the engine. Not sure what is telling the ECM to close the IAC. This is the work that has been done and parts:

No check engine light showing.
All vacuum lines have been replaced.
Fuel pump replaced.
Fuel Filter Replaced.
Fuel pressure gauge on fuel rail reads 42lbs.
TPS replaced and adjusted to .54 on voltmeter.
Ignition coil replaced.
Distributor cap and rotor replaced.
New plug wires.
New Spark plugs.
New Temp sensor.
New IAC.
Timing set at 6 BTC.

Thank you.

Bob88GTA

iTrader: (2)

When you did the procedure, and unplugged and started car, the idle should have been down around 400 rpm. Did you back the idle screw out to bring that idle down??

Bob88GTA

iTrader: (2)

You might even have air passages blocked in the IAC housing preventing air through passages. Might not be a bad idea to pull the TB and IAC Housing and check. JUST BE REAL CAREFUL WITH THE TINE TORX SCREWS, THEY TEND TO SNAP OFF. Soak with PB Blaster or equivalent and go easy.

Warm engine to operating temp, then shut off, jumper pins at ALDL

Turn on the ignition, but don't start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. Under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector is your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.

Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400 RPM with the transmission in "DRIVE" on an automatic transmission car, 450 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.

Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.

Then go into TPS set procedure

Throttle Position Sensor (TPS)

Tools needed:
1. Digital Volt-Ohm-Meter (VOM)
2. Breakout jumper wires or probes (make your own)
3. AutoXray, Diacom, or similar scanner will replace the VOM and jumper wires.

Turn on ignition, but don't start the engine.

With a diagnostic scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.07 VDC.

Connect the VOM to the TPS electrical connector terminals ‘A' and ‘B'.

With a breakout jumper: Disconnect the electrical connector from the TPS. Install the breakout in-line, between the TPS and wiring harness connector. Connect the meter probes to terminals 'A' and 'B' on the connector. (‘B' is the positive connection, ‘A' the signal ground, or negative.)

With probes: If you have very slender probes on your VOM, you can back-probe the TPS connector while it is attached to the TPS. If you have made probes of large dressmakers pins or a similar item, you can back-probe the connector as well. Connect the meter probes to terminals 'A' and 'B' on the connector.

Turn on the ignition to read the TPS output voltage at the idle position. The reading should be 0.54VDC +/- 0.07VDC. The ideal is the center of the range, 0.54VDC for a stock engine. To adjust the output voltage, loosen the two Torx screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, the TPS sensor may be failing and could be a cause of stumbling and driveability problems.

After achieving the desired setting, turn off the ignition switch. Remove all jumpers or the scanner and reconnect the TPS connector as required.

Pilotrick50

iTrader: (1)

Yes, that is the procedure I did with the IAC and TPS. I had the Throttle body off when I changed the IAC and I sprayed the inside with carb cleaner and blew it out. Tomorrow I will recheck the TB

Pilotrick50

iTrader: (1)

Ok, followed the procedure to set the IAC. and at the same time I checked the timing which was way off, I couldn't get it right on the money it kept jumping 4 degrees above and below. But anyways I can get it to idle but now you can't rev it, sounds like it's missing on cylinders and back firing. I still believe it's not getting enough air. I now have engine code 42 and 44

Pilotrick50

iTrader: (1)

Just an update for those following along. Replaced the ECM and that fixed majority of my problems. Cold start is real hard but once warmed up I can work with the car. Right now I am not getting a temp reading on my guage so I'm going to put a new sensor in because the voltage is not changing with the temperature increase. Also from a idle if I kick it down I get a backfire then it revs up. I have another distributor I am going to try. Been working a lot of hours lately and will send another post when I get a chance. If anyone knows if a fuel pump pulsator would cause a hard start let me know. Thanks for everyone's help so far, all the postings I have read really help putt an understanding to all of this.

Pilotrick50

iTrader: (1)

Ok, I have an update from this past weekend which is a significant improvement. I replaced the temp sensor (this was the 2nd) and it works. Even though I was told the distributor had checked out good I replaced it with a new one. That's as far as I got before stopping for the weekend. Today I went out and the car started a little easier, but vastly improved as I didn't have to hook up the battery charger to get it started. It went into a smooth high idle warm up at 1800 rpm as the IDC closed and Idle went to 1000 rpm it began surging from 1000 rpm to 1600 rpm. I unplugged the EST line and the car idled smoothly. As the car warmed up the idle dropped to 750 rpm and I checked the timing and I am between 4 to 5 degrees BTDC. I plug the EST line back in and the car continues to idle very smoothly. Now here's the latest problem: I follow the procedure to set the base idle and the engine idles at 1200 rpm with the IAC closed and unplugged and the idle screw is backed out not even touching the idle adjustment plate. If anyone has any ideas please let me know. Thanks

Gunsbee

Maybe try re checking throttle position settings.

Bob88GTA

iTrader: (2)

At this point, it sounds like you have a vacuum leak at the intake or runners SOMEWHERE. Its definitely sucking air from somewhere to be idling that high with the adjustment screw backed all the way out. Thy the butane/propane method on finding the leak. There is post on the site to tell you how to do it. In short, take a unlit propane/butane source with engine running and aim it all around sealing surfaces. When idle goes up even further, you found your leak. Also check all your vacuum hoses.

GL

Pilotrick50

iTrader: (1)

Ok, Checked all vacuum lines, everything is ok there. I sprayed carb cleaner all around the plenum and runners and had no drop in idle. I adjusted the idle screw out so it is against the the plate. I pulled another IAC from a running Trans Am and did the best I could setting the base idle at 700. With everything plugged in I am idling at 750 (5 speed trans) and my throttle response has improved but still lags at first but no backfiring is an improvement. That's all for today and we can look at things tomorrow.

Pilotrick50

iTrader: (1)

Yesterdays Events: Started car, cold start a little hard. While in high idle I got the check engine light for codes 12, 15, 44. I let the car warm up and as it warmed up it started surging between 1000 and 1500 rpm. I wanted to try and set the base idle and this is what I found. Jumpering the ALDL did not close my IAC, so I pulled it and manually adjusted it so it was closed. Started car and set base timing and set TPS to .54 with the new idle settings. Plugged everything in and it idles real nice at 750 rpm. I still have poor throttle response from and idle to half throttle where it will hesitate and sometimes backfire. But if you get it through that dead spot and get it revving it runs just fine. I did drive the care down my drive (450 ft) and turned around and backed across the pavement and aimed the car straight across from my drive, revved it up and dumped the clutch leaving two black lines across the road then shifted into second at the end of my drive throwing stones half way up that before letting up on the gas.... and lets say...she held her own!

Pilotrick50

iTrader: (1)

After everything I have a good start now, still a little hard but not bad and a fantastic idle. Currently I have the EGR valve plugged off which helped everything smooth out. I still have slight hesitation, which I will switch my focus on getting the EGR properly working first which I believe is the switch is getting a signal to open right away and staying open or the switch itself is bad. Thank you everyone for your help.

Pilotrick50

iTrader: (1)

The EGR switch is definitely bad so I bought a new one for a 1995 Cadillac Deville like so many people have done and I had an extra wire harness for my TBI and I found the the connector I needed for the Caddy switch and I cut it with an extra foot length so I have options on where I want to mount it. I also was able to order the Delphi "weatherpack" 2 wire female connector to put put on the end of my wires so I dont have to cut and splice my wire harness. I did a quick hook up to see how it worked and start up and idle was great but as soon as I gave it a little gas it started running bad and stalled so that tells me the EGR valve was sticky the whole time. Needless to say I have a new AC Delco EGR valve on the way and a new EGR sensor too. Hopefully everything will be here within a week and I will give you an update.

Pilotrick50

iTrader: (1)

It's been almost a month and it is DONE!!! My 305 TPI idles perfect. Starts right up now. I ended up following the tech advice and replaced the whole EGR system, cost about $130 all together buying parts from EBAY. I bought the 95 Caddy EGR vacuum switch, the temperature switch that threads into the EGR and a new AC Delco EGR valve. I also bought a female weatherpack connector so I didn't have to cut and splice any wires on the harness in the car. I had the connector for the new switch on a old wire harness and I gave myself an extra foot of wire so I can mount the switch anywhere now. My conclusion on all of this is the ECM was definitely bad along with the coolant temperature sensor and the EGR system along with the Distributor. Last but not least I put a fuel pump pulsator on, which works good as I see less fluctuation on the fuel pressure gauge. THANK YOU PEOPLE FOR ALL YOUR HELP!!!!

ChezeSammy

I had similar issues, among others, and the problem turned out to be the actual harness to ecm connection. Took the ECM down from behind dash and it took pressure off clip for time being and will need to reinstall with more slack. It runs perfect when that connection is good, and horribly when it isn't.

89 iroc 305 tpi

Pilotrick50

iTrader: (1)

That is definitely a first for me. So I take it that one of the wires are possibly broken or a pin is being pulled out. I got mine running real good now.