Italian Cars/Italian Cars Digest Archive
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MAD MARK2 <MADMARK2@domain.elided> wrote:
> Here's one that should be easy for anyone who's worked on a
> fuel-injected X1/9. I replaced the water pump on my recently
> aquired '83 model and removed the injection in the process.
> It runs well other than not wanting to idle after warmup but I
> had no idea other than trial and error how to line up the throttle
> plate indicator switch. Any suggestions??
If I'd have to say, a misadjusted TPS (Throttle positioning switch) is the
number one reason for drivability/idling problems on fuel injected Fiats.
When I first got my X 1/9, it would die 75% of the time when I pushed in the
clutch. Funny that it never did this on the day I test drove it. After I
adjusted the TPS, it never gave me anymore problems. Not the car itself but
dieing when I pushed in the clutch!
Here's how to adjust it along with other minor adjustments you'll probably
need to do.
With the engine off, loosen the two mounting screws on the TPS and rotate it
toward the exhaust manifold (clockwise) until you here a "click". Tighten
Next ever so slightly crack the throttle open. You should here it click
again within 1/16 to 1/8 of an inch.
To verify this and to see if the electrical contacts in the TPS are even
working, connect an ohmsmeter to the center contact (#18) on the TPS and
touch the other probe to contact #2. With the throttle closed the circuit
should show closed. With the throttle cracked it should read open.
This next step , I really don't know if it does anything or not But just it
case it does have a purpose ...
Have a friend hold the throttle to the floor (engine not running of
course!!) . Connect the probes to connectors 18 and 3. With the throttle
wide open, the circuit show read closed. At idle or cracked, the circuit
should read open.
I would imagine that when the TPS detects wide open throttle, something
miraculous happens, like the computer enrichens the fuel mixture or opens
the injectors at an almost continuous flow which should boost HP.
But I haven't found anything in any books to support exactly what happens
when the TPS detects WOT.
If the switch doesn't show closed at WOT, check to see what's causing the
throttle not to open up all the way. Like a misadjusted cable.
After the car warms up, it should idle at 800 rmps?? I've set both my Fiats
to idle at 1000 rmps (at warmup) using the factory tach. It idles best at
that setting. I've got a tuneup tachometer and have found that there is a
500 rpm difference between the factory Veglia guage and the tuneup tach! But
I'm not sure if the tuneup tach is really all that accurate.
If not turn the big screw clockwise to slow it down or counterclockwise to
speed it up.
If it is idling too fast and you have turned the big screw inward as far as
it will go, check to see if the short cabel has any tention on it. If so
someone may have taken the slack out of it to cure an idling problem once
before. Like they did on mine. I don't think it's written anywhere but it
should have a little slack in it but not too much slack nor too tight.
If that doesn't work, unloosen the small 8mm nut on the throttle stop set
screw and back it out slightly until the engine dies then tighten the 8mm
nut on the stop screw. Then turn the big screw outward several turns.
At this point you will probably have to re-adjust your TPS since you
disturbed the setting.
If the TPS is out of adjustment, reset it.
Then adjust the big screw until you reach 1000 rmps or until the engine
I still haven't figure out why I have to periodically adjust the idle on my
Spider. Seems like every 3 to 4 months I have to readjust it. Last time, I
set the idle to 1000 rmps and today it seems to be idling at 800 rmps. Seems
to be related to the change of seasons.
I wonder if those 80W/100W H4 bulbs I installed are causing the alternator
to work harder thus reducing the idle?
I also have never figure out why I have to periodically tighten the lower
radiator hose clamp every so often. I know when it's time because I notice a
small leak on the splash pan. I was able to turn it, 3 turns the other day.
Maybe engine flex?
As far as the adjustments on my X 1/9 are concerned:
When I first got it, it would die when I would push in on the clutch. I
adjusted the TPS and the idling and took care of that problem.
The car was still blowing black smoke from the tailpipe and leaving a sooty
puddle on the pavement when idling. Boy, the smog Nazis in California or
Arizona would have had a field day with this thing!
So then I tuned it up (new plugs, plug wires, distributor cap, rotor button).
I used a distributor cap intended for a VW rabbit (long story about that
one) so I got two of the plug wires crossed and flooded the engine.
Afterwards it started idling at 3500 rmps and developed a perfect slope like
a fuel injector wasn't working or a plug wasn't firing.
I turned the stop screw and the idle screw (big one) both all the way in but
still idled too fast.
After awhile I found that some ingenious mechanic had tightened the short
cabel to the point to where the the throttle plate wouldn't close off. I
took the slack off the cabel and corrected that problem.
Next I installed a new O2 sensor and got rid of the smoky exhaust. Now the
car runs like a top and the gas mileage is up from 20 mpg to 33 mpg.
This is the only known case I know of that an O2 sensor replacement actually
made a difference on a Fiat. I figure if the fuel injection system is in top
shape, the O2 sensor won't make a hill of beans but if the air flow meter,
coolant sensor, etc. is not reading properly the O2 sensor should correct
any variances in the system. I've installed new sensors in Spiders which
made no difference whatsoever.
I also installed a long spring from the point where the main throttle cabel
connects to the "rod" that runs across the valve cover to the fuel rail
mounting bolt. Something is causing the throttle to stick open. Possibly due
to the throttle plate being misaligned or bent which was probably caused by
the stop screw being fiddled with at one time or another.
The throttle still ocasionally hangs open at 4000 rpms but is much better
I know that installing the spring is not actually fixing the problem, but it
did the trick.
The throttle is really tight now!
Hope that helps.
James Seabolt -----> mailto:firstname.lastname@example.org
1980 FIAT 2000 Spider (injected)
1981 FIAT X 1/9 (Injected)
1994 JEEP Wrangler (2.5l )
1976 Chevrolet Pickup (454 Big Block)
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