First, off, though, the car runs far, far better with the rebuilt distributor. The smoothness at idle in gear that was never there now is. The car also is far faster than it has ever been. And I don't even have the timing set properly -- I just earballed and got it close. I will time it this weekend.
So, after 15 minutes of driving and the engine up to working temperature the idling starts wandering and the ICM changes the timing to compensate, same as before, but not quite enough to make it stall.
So, nothing really has changed with the idle situation.
Again: no trouble codes.
I have not checked the fuel pressure, but I can't see how that would make the ICM adjust the idle, and the ICM can change the fuel pressure.
The last thing I am going to try before I get rid of the car is a new ECM. They are cheap enough.
It might be easier to mark the balancer from underneath the car.
Absolutely. The balancer has three marks, each 120 degrees apart. By raising the car and looking underneath, its much easier to tell which one is which (you want to mark the WIDE one), as opposed to peering down from above where you have just a tiny, narrow little view.
Rich, by how much RPMs is the idle fluctuating from 900RPM?
What shape is the harmonic balancer on this fiero? Make sure the rubber insulation is not cracked or dry rotted away. The balancer can't be loose or rotate clockwise and counter-clockwise. (back n forth)
Fuel pressure spec on the fiero 2.8L is between 40.5 to 47psi. You can check this by access to the Schrader valve with a gauge on the fuel rail next to the thermostat housing. I have a fuel gauge mounted on my fuel rail, and honestly I like the idea of having it. I can monitor the pressure when the deck-lid is open / engine running, and see the pressure when the engine is stopped.
The harmonic balancer looked fine tonight. I see nothing abnormal there.
The idle goes like this:
Smoothly at first 850 900 RPM in gear, foot on brake.
When the engine is hot...
The idle starts to wander, down a bit, then up to 1,000-1,100, then it starts slowly sinking, when it gets to 750, it jumps back to around 1400 and then starts down again. I have a small exhaust leak and I can hear the tone of the engine change to very labored running, as if the timing was too far advanced or retarded. Then the idle gets slightly rough as the engine gets hotter. Then idle sinks into the 600 to 700 range. The lower it sinks the more the timing changes to bring the idle back up.
I am convinced the timing is jumping around when the engine is hot. When the engine is at normal temp I can see the tacho needle getting jumpy. It seems an electrical issue related to the ignition.
But if the fuel pressure is dropping slightly when the car is hot, would that cause the ECM to make the engine run faster by adjusting the spark timing?
[This message has been edited by Rich Truett (edited 05-16-2015).]
I have not cleaned the existing grounds, but I have tried adding an additional ground from the battery directly to the engine. Makes no difference.
Tinkered with it tonight. I reinstalled the factory EGR valve.
That has helped a bit. She's really running well except at hot idle. Now it won't stall, but the speed drops and it runs roughly, almost like it is missing.
When It was at this point, I tried: Disconnecting the IAC -- no changes Unplugging the MAP -- no changes Connecting the ALDL -- no initial change, but then when I undid the ALDL, the RPMs increased from around 800 to 1300 and the engine smoothed out; in a few seconds it settled into a nice, smooth idle at 950. But it couldn't hold that, and then eventually started idling roughly again.
There is one code: 44. But I do have a small exhaust leak.
Rich, if you have code 44 set, check the following...
The ECM will set code 44 when the ECM detects a low voltage from the oxygen sensor and the system is operating in Closed Loop (conditions must exist for longer than 20 seconds).
Check the wires of the oxygen sensor, making sure they are not in contact with the exhaust manifold.
Check the oxygen sensor and replace if necessary.
Check the MAP sensor. If the ECM detects a higher than normal vacuum then this will cause the system to go lean. Disconnect the MAP sensor. If the lean condition goes away, then a problem exists with the MAP sensor.
Check for lean injectors.
Check for fuel contamination (specifically for contamination with water).
Check fuel pressure. If pressure is too low, the system will be lean.
Check for exhaust leaks. An exhaust leak can cause air to be pulled into the exhaust and past the sensor.
Was the car up to operating temperature when you actually set the timing? Did you have the parking brake set and the car in gear when you set the timing? By your statement that "in gear, foot on brake" it's an automatic?
The V6 has a lot of small plastic vacuum lines that could have a small crack and start leaking when warmed up and the cruise control also has vacuum lines that could leak. If you have already checked these good, otherwise I would. The exhaust leak does also affect the idle and what the ecm thinks is happening.
Out of curiosity, did you change the plugs and wires when you changed your distributor? The heat may be causing weird continuity or resistance issues as the temp goes up. Does it sound like it's misfiring? Also, How are your electrical grounds? You should add an extra ground to wire from your engine block to the body as seen in this thread.
------------------ "Discord" Red 1988 GT under restoration!