day 1 ran fine, day 2 no idle

[paook]

Sunday, I drove our 1980 FI spider around town without problems. Monday, it started but with a "zero" idle. Weather was identical between the days. We didn't touch the car between the Sunday drive and the Monday attempt. Any hints as to where I should start looking? I was going to look into the TPS first, but it doesn't seem the most likely candidate.

Symptoms:
The engine fires up fine, and as long as you keep your foot on the gas pedal a bit it will purr like a kitten. I was able to keep it at about 1400 rpm by this method, any less (hard to regulate) and the engine would instantly die.

Without the gas pedal depressed, the engine fires, but dies right away. Doesn't sound sputtery.

Tightening the idle cable adjustment (from where it ran fine Sunday) so that the TPS is just clicked, the engine fires up fine and runs at a high idle (2000 rpm-ish). I tightened the throttle cable by the width of one nut (swapped which side it was screwed on) and another 2-3 threads.


I should have known something would happen. Today is the end of our self-imposed two week "new top stays up so it sets well" period. I was hoping to drive it to work with the finally sunny Seattle weather!

[azruss]

sounds like a dying cable issue. might want to check both ends, or look at the grommet at the firewall.

[So Cal Mark]

the throttle cable should not have tension on it. I'd suggest you might have an air leak

[paook]

We replaced all the air hoses, as they turned out to be cracked at the joins. That didn't solve it.

We can get the car to run at a rough 'idle' (via gas pedal) around 1000 rpm, with the air flow sensor disconnected. Is there any harm in driving the car like this for a mile to get it to a pro? The screw adjustment at the air meter didn't change anything, it was already maxed out clockwise. A posting on a Russian forum then led my wife to pull the sensor wire.

I've gotten frustrated with trying to fit the Fiat fix in with other house repairs, and the very short Seattle summer this year. Don't want to miss the driving season!

[rlux4]

One thing you could try is cleaning the AFM resistor track with rubbng alcohol. Look closely at the track, there will probably be two spots worn more than the rest of it. One where the arm sits at idle and the other where it is at cruise. If the spot at idle is bad it's you problem. Move the sweep arm up or down on the shaft so that it moves on a different track. There's a little bolt that tightens the sweep arm to the shaft, just loosen it, move the arm and then retighten. If you move it up the shaft watch that you don't lift the arm off the track.
Let us know how it goes.
Ron

[paook]

We popped open the AFM and cleaned/adjusted it to ride a better arc. Slight improvement in lowering the RPMs that can be held steady, but didn't solve the problem. We drove it (plenty of stalls) to a local Euro mechanic today and we'll see what they can do.

[ORFORD2004]

I suspect the temperature sensor in the AFM and you can spray WD40 on the track of the AFM. The WD trick solve my problem on the second one i install in the car. Since i will go on megasquirt soon, it will be availlable

[paook]

Just got the car back from the shop and it works now.

The day we drove it to the shop, the condition was the worst yet. It would not run well at even moderate RPMs, with the throttle position sensor tricked (throttle cable tightened beyond idle). The car stalled about four times in the mile to the mechanic.

End result of their diagnosis is that the throttle position sensor was outputting bad signals at the low end. We supplied a new Bosch TPS and they installed it, rather than us try to make the car limp home. Bad idle solved! Now we finally get to drive the car the first real time this summer....top down, sunny skies... Wonder what will break next? (Aside from the vent window latch which the shop broke and didn't admit to )