Thanks for viewing. I just bought myself a 92 z28 maybe 2 weeks ago . When I went to buy it, the car ran great. It would stall every now and then while driving, but the po assured me it was the iac valve needing to be replaced and that there was one on the way. That made sense to some point. But the engine seemed solid. On the drive home from buying it, it stalled and wouldn't start again. Now every time I drive it, it runs fine when first started and by the end of the street it wont idle on its own. Every where I drive I have to keep my foot in the gas a little. It doesn't want to accept full throttle at any time and it backfires on decel like I'm doing a drive by. But that might be from the full exhaust with cut outs that may be leaking. Also I noticed the whole distributor rotated freely. I ran the car and rotated it til the timing mark was where it needed to be. I don't know how much that affects it all?

I'm replacing the fuel filter and cleaning out the iac until the po gives me the new one. I was just wondering if this is a common problem and if there's a common fix. Maybe there are certain things to look for? I don't know . Just looking for some advice from the third gen gods.

Engine is a 305 multi point fi. Car's green. Tires are black. Thanks in advance!

 

Your CTS could be bad. That would also dump gas into the engine because it thinks it's cold. Is it stalling on it's own, without warning? I had that issue and it turned out to be the pick-up coil inside the distributor. You could also have a bad ICM.

If your distributor is moving by hand, get a timing light, disconnect the est, and set it to base timing (should be printed under your hood, on the front of the hood). Do that first and go from there. You don't want to be chasing some random problem that's being compounded by the fact that your timing is off...

Good luck and keep us posted with your findings!

 

I HAVE A SIMILAR PROBLEM. ENG STARTS / FIRES AND IMMEDIATELY STALLS. ENG WILL IDLE IF OPEN THROTTLE PLATE A SMALL AMOUNT. POWER IS GOOD AT HI TPS POSITIONS AND ENG RUNS STRONG AND SMOOTH ON HIWAY . ALL IGN PARTS HAVE BEEN REPLACED . FUEL PUMP AND FILTER REPLACED. TIMING RESET TO FACTORY SPECS ON HOOD. CTS REPLACED. PASSED EMISSIONS 2 MONTHS AGO. THROTTLE CRACK W/ DWNSHFT IS GOOD. I SUSPECT THE IAC. ILL POST MORE WHEN I TEST IT.

 

So here's an update. I replaced the fuel filter. Ran to sheets (about a mile) for some milk and ice cream. Came back out and it wouldn't start. The next day I went back to get it and it wouldn't start until I pulled the connector on the iac. All this time it seemed to idle perfectly. Today I cleaned the iac valve and took it down the road with the iac plugged in. Got up to 3rd gear, then to a stop sign and after I put it in second, it completely shut off. Wouldn't start again.

I cant figure it out... It seems like it wants to crank over great. It seems like it is getting fuel. Just doesn't want to fire over. I set the timing mark on the belt where it needed to be.

Im starting to not like this car anymore... left me sitting 4 times already in 2 weeks... I'm envious of those nice working new cars, but who wants that when you can have a sweet camaro?!!

 

https://www.thirdgen.org/tpimod2
Give that a go if you haven't already. Quick question, what do you mean by "set the timing mark on the belt"? If you've messed with the timing at all, did you disconnect the EST first before adjusting it? I only know of one way to set the timing without a timing light, and that's using marks on the distributor itself (not that there aren't more, so feel free to correct me ).

 

Inconsistent Idle

The first and most telling symptom of a failing TPS is an idle that rises and falls sporadically or maintains a very high or low RPM. This condition can be extreme enough to cause stalling or to cause the tires to chirp when the transmission is engaged. It can be difficult to tell the difference between a failing TPS and a malfunctioning or clogged idle air control (IAC) valve, so electrical testing of both sensors and cleaning of the IAC is recommended.


Maladjusted TPS

The TPS must be adjusted (rotated) so that it reads idle and full-throttle positions properly.
It should be 0.54Volts at IDLE (+- .075V) and 4.0 to 4.9 volts At WOT



IAC and TPS Adjustment

Tom Keliher Mar 31 2006 - 3:07pm

Idle Air Control (IAC)

Tools needed:
1.Torx bit # T-20
2.Paper Clip
3.Small Punch

Take the paper clip and open it up and form it into a big "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' pins.

Turn on the ignition, but don't start the engine. Wait 30 seconds. Now, go remove the connector from the IAC.

Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to 450 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.

Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive (for unmodified cars).

If you set an SES light by having the IAC disconnected, then after shutting down the engine disconnect the negative battery terminal. Wait 5 minutes. This will clear the ECM of all trouble codes. Re-connect the battery and drive the car for 20 minutes to allow the ECM to relearn your driving style.


Throttle Position Switch (TPS)

Tools needed:
1.Digital Volt-Ohm-Meter (VOM)
2.Jumper Wires (make your own)
3.Auto Xray Scanner (if available) will eliminate the need for VOM and jumper wires.


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

With a scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.075Volts

With VOM and jumper wires: disconnect the connector from the TPS. Using your jumper wires, make a connection allowing some room for the VOM terminals to contact the jumper leads and read the TPS voltage.

If out of spec, loosen the two 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, that could mean a bad TPS switch and could be a cause of stumbling and drive-ability problems.

After setting the correct voltage, turn off ignition switch. Remove jumpers/scanner and reconnect the TPS connector as required

 

get the IAC motor and when you replace it you have to calibrate it as described.


Also the distributor should not rotate by hand, someone was playing with timing and did not tighten the hold down bolt. make sure the hold down bolt and bracket are there... it's a "U" shaped braket that clamps the distributor to the intake manifold to keep it from rotating and throwing off the timing.


get the timing correct first...

 

Ok. Today I got the iac valve from autozone and put it in. Tomorrow I'll try to do some of the things ransford and frmula suggested. Then I'll tackle the timing. When I tried it the first time, I moved the distributor so that it was running, then I rotated it until the timing light showed the timing mark on the belt in the correct position. I know that's not the right way to do it. So I'll do it the right way tomorrow.

It just sucks because I don't have a lot of time to mess with it after work. And mosquitos suck big time!!! (no pun intended...)

Thank you all, for the help so much! It's really great to know there's a good forum full of good people out there! I know I'm not the first person with this problem and I'm a noob and all, but you guys have been more than helpful! Thanks!

P.S. My newbie-ness doesn't know what the "aldl" is...