Poor Acceleration & Idle

[DogRocker]

I have a 1981 FI that may have multiple problems. I just got this car about three weeks ago and don't know much about the history. When I first got the car it had some intermittent starting problems. I added a relay and gear reduction starter. So far, so good.

Next I was trying to figure out the warmup low idle issue. Cleaned the AAV and it now has a small opening when cold and closes when hot. Seems semi-ok - I think.

Meanwhile, I was going through the FI Tune Up procedure here: https://www.mirafiori.com/faq/fiatFI_may2002.pdf and noticed a few things:

1) Measured 3500 Ohms between pins 7 & 8 on ECU cable. I removed the AFM, opened it up and found that the resistive element had a pair of fairly worn tracks. I adjusted the wiper arm so that it would ride on a fresher portion of the resistive element. After moving the arm slightly and making sure all the contacts were clean, the closed door wiper arm (pin 7) resistance reading was now around 200 Ohms. To further test, I hooked up a 5 Volt power supply between 6 & 8 and monitored pin 7 using an o'scope. I now had smooth voltage ramping up and down as I moved the door opened and closed. While in there I checked the fuel pump switch and gently used a heat gun to measure air temp resistor. Both good. I also found that the door stop was a little bent and the flap was slightly crooked which left a small gap when the door was in the closed position. I straightened the door stop and the door is now fully closed when no air moving.

2) I replaced the cap, rotor and plug wires (one of the old wires had electrical tape wrapped around it), fuel filter, oil & filter change.

3) All the other reading (coolant temp sensor, thermo time switch, TPS) taken at the ECU cable under the dash were ok according to the manual linked above.

4) I sprayed carb cleaner around all the air hoses looking for leaks. Nothing obvious other than one slightly loose hose clamp.


Two other things I noticed...

A) The Idle Speed adjustment doesn't do anything. I removed the screw and inspected the o ring. I sprayed carb cleaner in the hole. I removed the screw completely to see what difference it would make. Nothing changed the idle. The idle screw is currently screwed in all the way as I found it.

B) The Vacuum Advance shaft connected to the distributor doesn't seem to move when throttling. Last night, I removed the vacuum hose from the throttle body end and tried sucking air. I had to pull pretty hard, but I got some movement. I kind of expected more movement for some reason. While running the engine with the hose disconnected from the distributor, I put my finger over the end of the hose to see if there was any vacuum while accelerating. None. Obviously, this is a crude test, and I really should get a vacuum gauge. On the shopping list.

Things I haven't checked yet:

1) Spark plugs. Just haven't got there yet.

2) Timing. I'm borrowing a friend's timing light.

3) Valve adjustment.

4) O2 sensor.

Later this week I'm scheduled to take the car back to Performance Apex in Renton, WA (http://performanceapex.com/index.html) where the previous owner had Ray (owner/mechanic) rebuild the motor about six years ago. I'm hoping he can shed some light on issues. Since the car needs to stay somewhat drivable I'm hesitant to do much more tweaking, however this sluggish performance is bugging me, and I'd like to at least listen to ideas. Any ideas?

[PhillySpider]

Does the flap in the AFM move FREELY? Mine was sticking...some light sanding in the tunnel took care of it. Symptoms were very little power, starting troubles intermittently, and surging under throttle.

[DogRocker]

Yes. The flap moves freely. No jerkiness or scraping, just smooth.

I got a vacuum gauge last night, disconnected the throttle vacuum line that connects to the vacuum advance on the side of the distributor. It's zero at idle as expected. However, when I move the throttle open it moves up slowly and gradually. That seems weird to me, but it may not be. Dunno. I only had a few minutes to fiddle with it last night.

[tima01864]

Ever find a cause or solution?