New Symptom - On way home from Club meeting

[MetalBlue85GT]

Car - 85 GT 2.8 stock Automatic. no known engine mods.
- I have not replaced anything in the ignition system.
- i have not checked timing yet.
- this is the first time this has acted this way in 500 miles since I bought it.
- Only engine work was to put the EGR system back to stock (uncapped it).


After good food and good company ~ my son and I started off for the forty mile drive home. In stop and go for about 20 minutes speed started to pick up and we were cruising about 60. as i accelerated slowly the car would start to stall and then fire back up and run fine; when I woudl settle in to cruise again and accelerate it woudl load up stall and fire back up and act fine.

So here is where I started my troubleshooting: I was @ cruise about 60mph, pushed deeper into the pedal this time it full an stalled and then backfired when it lit back up. Once it recovers from teh stall it is normal with all the power and response. But once i keep a steady pedal for a short time and accelerate it does this. Once I was off the free way i tried it at cruise at 35 - same results - 45 same results.

I have it parked in the garage at this time and I am thinking I am goint o take it on a local ride to see if it is still there after a cool down as start up again.

After I hear back from you fine fiero owners I will decside where to begin.

Timing, Plugs, wires, cap, rotor.

What are your preferences on Plugs. Mine in my boat are iridium - I was thinking the same due to the higher RPMs of the 2.8 Auto on the freeway.

[Fierofool]

For some reason the Fiero likes the original stock plugs gapped at .45.  The fancy plugs just seem to give problems.  AC Delco R43TS6 would be the correct ones.  I've run into some discrepancy on the plug gap.  My 87 owners manual that came with the car says the gap should be .60 but the decal underneath the decklid says .45.  All my other cars also have .45 on the decklid.

Stall out at acceleration can be the TPS or maybe the MAP sensor.  Timing would be suspect unless it just started suddenly.  Be careful on the TPS.  The attachment screws are aluminum and tend to break off in the throttle body.  You can't drill them out and tap for a larger size because the TPS won't accept a larger screw so the only way to repair is to install a thread-sert, which would require removing the throttle body.  SO, I'd mess with the TPS as a last resort. 

[MetalBlue85GT]

Thank you MAP sensor will be first and easiest. it doesnt make sense that it would jsut start doing that while it is still purring so nicely at every other point.

I forgot to mention - Pervious owner removed catalytic and recently replaced O2 sensor howerver since it was running soooo rich with the EGR capped maybe that is a nother place to look. I will get both and change them one at a time to see if that works first.

And no Check engine light yet since I bought it.

[CowsPatoot]

Have you verified the Check Engine light works?  Does it come on for the self-test when you first turn the key?

[Fierofool]

The catalytic converter wouldn't have any effect on anything but sound.  A common cause of excessive rich mixture is the Coolant Temperature Sensor.  It will usually cause the exhaust to burn your nose and eyes.  We have a temperature sensor values chart in our tech tips section that gives ohm resistance at various temperatures.  If your CTS is saying the engine is cold it will tell the ECM to increase the fuel flow.  It usually won't set a trouble code, either. 

Check the vacuum line coming off the MAP.  If you have a MightyVac hand vacuum, pull about 5 inches of vacuum to see if it leaks down.  Could be a small crack in the line.  These are just some of the areas that can cause a stumble when you accelerate.  Check all the vacuum lines that connect to the intake.  There are two that are difficult to find underneath the throttle body and the neck of the intake.  Make sure they're well connected. 

Removal of the EGR system can also cause backfires if not done correctly as can vacuum leaks.

[Fierofool]

Just found this on Pennocks.  Might be helpful.   http://www.fiero.nl/forum/Forum2/HTML/128023.html

[Raydar]

I'm inclined to think it's the TPS, or related.
The TPS responds directly to throttle input.
Think of it this way: On a carb, you have an accelerator pump. On EFI, you have the TPS, and the ECM and injectors responding to it.
The injectors have to provide an electronic "pump shot". The TPS is the only thing that moves quickly enough to make that happen.

[MetalBlue85GT]

So the test drive - I drove it to work this am in traffic and in some of the same crusing speeds. no repeat. - When i drove it home same thing which was no repeat of the symptom.

I will tinker with it over the next few weeks and post what i find here. I love the mightyvac idea - i do have one...

good times

[TopNotch]

Have you replaced your fuel filter?

[MetalBlue85GT]

Previous owner said he did but thats another good idea. I will have to look into that one.

[MetalBlue85GT]

So shortly after I started this Thread I had the Ignition module fail. Since I didn't have any symptoms after that drive home from the Club meeting I just assumed that it was tied to that some how. So after two - three solid weeks of driving to and from work it happened again. It was a hot 90 degree day with the AC running and same symptoms again at cruise any speed if I accelerate; slow or fast; it starts to stall, if I push harder is stalls harder. if I back off it catches:

but something new happened - It did not seem to down shift properly when I came to a stop and stalled the car. it starts right back up but I put it into gear it stalls again.

I cycled the auto shifter through all gears and then tried again and it down shifted and started to act normal then it will do it again as I came into my neighborhood and stopped at stop signs. I let it sit for a week before I would drive it. I took it around close on a cool day and nothing. So I drove it June 28th to work and in the morning nothing but again its back on the way home this time with no AC running. it was a hot day Friday.

I also noticed that this happens when the cars temp gauge is elevated a line past what it normally sits at.

All this may not be related but just wanted to share.

Here is the list I am going to start now that its back two times in a row:

-MAP Sensor and vacuum hoses
- Plugs, Cap and rotor
- Fuel Filter
- last resort TPS - And I am reading the Pennocks link now.

[TopNotch]

but something new happened - It did not seem to down shift properly when I came to a stop and stalled the car. it starts right back up but I put it into gear it stalls again.

It's the torque converter control (TCC) solenoid. Not to hard to replace. For a temporary fix, pull the blue wire on the firewall side of the transmission.

[MetalBlue85GT]

I will try that this week seems easy to troubleshoot - I just have to go drive it for 30 mins in stop and go traffic.

[MetalBlue85GT]

Pulled the wire  and no issues. Thanks for all the help.

That is next on my list of to dos; probably over this weekend.

[TopNotch]

Your fuel mileage will suffer with the wire disconnected, since the torque converter will not lock up. And your car may over-heat if you drive it hard. But at least, you can drive the car.