91 Festiva high/strange idle when warn

[Dodgeih]

Hi, I have a 1991 Ford Festiva. It has a 1.3 liter engine with a 5-speed manual. It idles high all the time I would say somewhere around 1700 RPM just guessing. After it warms up when I am coasting to a stop it idles up then seems to cut out for a second and repeats this until I come to a stop. It also revs up right when I push in the clutch as if I'm pushing in the clutch too quickly but I'm not. I have zero experience with these cars as I just picked this up as a beater while I rebuild the engine in my 01 Cummins. Any advice or Insight would be appreciated thanks

[william]

Sounds like the Iac is going crazy.
I would try cleaning it.

[FestYboy]

Check that there are no leaks between the IAC and TB, then locate the base idle screw on the TB ( front right corner of TB as you look from engine bay), it's a flat tipped screw that sits inside a vertical tube that is usually covered by a small rubber dust cap. Screw it in all the way and then back off in 1/2 turn increments untill idle is ~ 650 warm.

[Dodgeih]

Put smoke through the system and had no vacuum leaks anywhere. I'll try cleaning iac and adjusting the screw

[Dodgeih]

Well I cleaned it out.. Nothing seemed to dirty but who knows. I got the idle to sit down better with that screw but I have not and will not have time to drive until tomorrow unfortunately. I will see if the rev up between shifts is better and if it still goes up and down at all... I cleaned out the maf like thing on top of the air box as well...

[Dodgeih]

So I got the idle better, but that's it.. It still revs up and down after it's warmed up like when coasting to a stop and the first 30 seconds or so after you stop...

Also another question, is the diaphragm on the throttle lever that helps it to idle down slowly necessary? Would there be any negative consequence to removing it?

[FestYboy]

That's an odd question... Or more accurately, oddly worded. But I'll ignore that for now.
Since the base idle screw had an effect, the next step would be to clean the throttle plate and barrel, and then check it's closed position with feeler gauges. Once it's verified that things are within spec, the last piece of the puzzle is the TPS.

[Dodgeih]

I have already cleaned the throttle plate...where can I find the specs and what exactly am I measuring? How closed the butterfly is?

I see that after comma would have helped my other question. What I'm asking is if the thing on the front left of the throttle body(when standing looking at the motor) can be removed or what purpose it serves? It appears to bring the throttle plate to a closed position more slowly on last degree or two... But wondering if I can take it off

[FestYboy]

Ok, with the way it was stated earlier, my gut reaction was that it was already removed.

The Dash Pot (proper name), does exactly what you describe. You want to keep it there for a few reasons, the biggest being that it keeps the plate from jamming into the TB bore and sticking the throttle shut. Even with a throttle stop, the plate has enough momentum from a WOT position to flex and jam in the bore when let to snap close. Then there's the interaction with the VAF... Snapping the throttle shut without it can cause the VAF to bounce which can affect driveability.

As for the feeler gauges, that's exactly what you're measuring. If it's out of spec, the plate could be bent, or the cable adjustment too tight (likely the latter). Once that is verified, the next step is to verify TPS signal and position.

[FestYboy]

Ok, with the way it was stated earlier, my gut reaction was that it was already removed.

The Dash Pot (proper name), does exactly what you describe. You want to keep it there for a few reasons, the biggest being that it keeps the plate from jamming into the TB bore and sticking the throttle shut. Even with a throttle stop, the plate has enough momentum from a WOT position to flex and jam in the bore when let to snap close. Then there's the interaction with the VAF... Snapping the throttle shut without it can cause the VAF to bounce which can affect driveability.

As for the feeler gauges, that's exactly what you're measuring. If it's out of spec, the plate could be bent, or the cable adjustment too tight (likely the latter). Once that is verified, the next step is to verify TPS signal and position.

Addendum: the throttle position measurements are taken at the throttle stop (which is NOT to be adjusted). Taking a 0.020 (0.5mm) blade, place it between the stop screw and arm. Then, with the TPS plug removed, check the lower 2 terminals for continuity. If there is none, rotate the TPS untill continuity is achieved. Then, with a 0.027 (.7mm) blade perform the same test. There should be NO continuity. Adjust the TPS untill both perameters are met.

Also while looking for the specs, I came across a note that a failed ECT sensor can also cause poor idle quality when warm (located on the intake manifold between cyl 1 and 2).

[w4rkry]

Failed ECT was what was causing literally every bad running issue I had with mine. Over a year of rough starts, high fuel use, random losses of powers and dying, all solved with an 18 dollar sensor.

[Dodgeih]

I adjusted the dash pot to a "less effective" setting. It was touching the throttle lever well before it should have in my opinion. There was probably almost a 1/4" of travel left when it touched. And I adjusted the tps that was not in spec. It has helped everything, even the revving up and down but it has not stopped it completely. I will double check the tps in the next few days when I get a chance

[Dodgeih]

Failed ECT was what was causing literally every bad running issue I had with mine. Over a year of rough starts, high fuel use, random losses of powers and dying, all solved with an 18 dollar sensor.

Did the gauge on the dash seem to work correctly?

[w4rkry]

Did the gauge on the dash seem to work correctly?

Only sometimes. It's never been accurate. I think the gauge even uses a different sensor if I recall correctly.

- Korean Note 4 via Tapatalk -

[FestYboy]

Did the gauge on the dash seem to work correctly?

They are separate circuits and do not interact.