1989 carb'd Festy "fast idle" won't slow down

[AlaskaFestivaGuy]

I've got a 125,000-mile LX at a remote site, and it's been running perfectly until the last few weeks when it's been taking longer and longer for the fast idle to slow down. Now, it stays up around 2,500 rpm or so.

It would seem that something somewhere has been sticking, and now is completely stuck.

I don't have my Haynes manual or any paperwork with me.

Are there obvious things to try? What controls this ... a temp sensor somewhere. Is it part of the vacuum advance system, or something independent of that?

Temps haven't been cold at all ... mid 40s lows and 60s to 70s during the day. It even happens when it's 70 now.

The site is at an altitude of over 4,000 feet, but that hasn't been a problem since arriving here.

[WmWatt]

Oop's I see it's an LX, fuel injected. Can't delete, can only erase.

[AlaskaFestivaGuy]

It's carb'd. My understanding is that only automatic 89s were fuel injected. This is a manual.

[WmWatt]

Mine's an L. I thought that was the carb'd model and the LX was fuel injected with the automatic transmission. I guess you know you can tap the accelerator to release the automatic choke? And spray the carb and linkages with carb cleaner to make it less sticky? After that I suppose the next thing would be checking for vacuum leaks. I don't know enough about the vacuum hoses to suggest which might influence idle speed.

[ricko1966]

Check to see if the choke is closed or open when it is idleing too fast.If the choke is closed it is suppose to be on fast idle.If choke is staying on too long first make sure it isn't just sticking and needing cleaning.Make sure you are getting power to the choke element and check the element for continuity.I would set the choke so it is fully open ASAP.If the choke is open and you have a high idle start looking fir vacuum/intake leaks propane or spray carb cleaner is a great tool here.

[AlaskaFestivaGuy]

Kicking the accelator doesn't knock it off the fast idle; in fact, it often speeds it up by 500rpm!

Today, I'm going to remove the air cleaner base to expose the carb and lube everything I see.

[bravekozak]

You are dealing with a feedback carb. The actuator is controlled by the computer.
You must change to an Escort carb to bypass the computer.

[AlaskaFestivaGuy]

I pulled off the entire air cleaner assembly for a look-see.

Everything is squeaky-clean and all linkages moving freely. All hoses are nice and soft, obviously original due to molded shapes and color coding. Not surprising, since it was a SoCal car that I bought earlier this year from the original purchaser.

I nevertheless lightly lubed the linkages.

I started it up with the air cleaner off and got 2700rpm in 70 degree temps. The rear opening in the carb was blocked; I presume that's the choke. I opened it by fiddling with the green linkage, causing rpm to come down to 2200, but it would not go any lower no matter what I did.

I'm guessing that this is some sort of sensor problem, else the computer (I'm surprised the carbies are computerized at all) has gone brain-dead.

Anybody have any suggestions about what to do? The car needs to stay at this site and used daily for another few weeks before the two-day drive home.

BK, this is one of three mint-condition LXs I have which I plan to upgrade to FI in the future using bad-body FI donors I already have, so switching to a simpler carb type isn't particularly appealing as a solution.

[WmWatt]

I don't know enough about carburettors to diagnose a problem logically but that wouldn't stop me from going around wiggling hoses and electrical connections and tapping on things with a wrench, pausing for effect after each one before moving on to the next. I don't know if the EGR valve makes any difference but you can reach under it and push up gently with a finger tip to see if the diaphragm moves (if sticky it can be taken apart and cleaned). There's the three colourful plastic solinoids on the firewalll. There's a white metal cylinder at the front left with four hoses coming out of it which is supposed to moderate speed changes when you stomp on or take your foot off the gas pedal, I think. It doesn't come apart but it can be tapped to see if it's stuck (air cleaner needs to be off to get at it IIRC). There's something at the back which gives the engine a spurt of gas to keep it from dying during acceleration or something. I'd try pushing or pulling on that to see if it's sticking. Its one of the things I spray with carb cleaner. There an air bypass(?) diaphragm on the silver thing attached to the left of the air cleaner. I think you can turn off the computer by grounding a wire or by disconnecting the oxygen sensor. That puts the car in "loop back" mode running without the computer. It might also turn on the check engine light. Happy hunting.

[WmWatt]

On second thought there are some things you can eliminate. Fast idle means too much gas or too little air, I think. For example, if you're looking for vaccum links and spray with propane a leak makes the engine speed up. In your case a vacuum leak would be sucking air. That would not speed up the engine so you don't need to check for vacuum leaks. I'd concentrate on air blockages or gas leaks or bad mixutre. The EGR recirculates exahuast to cool the cyclinders so maybe that's not an issue either. I'd check it anyway. The computer controls air fuel mix after the O2 sensors warms up. Your problem is on startup so maybe the computer is not at fault, or the O2 sensor, or its wiring. Hope that helps.

[AlaskaFestivaGuy]

I'd already pretty much tapped and wiggled everything. As I indicated, this is a very clean car. Also, I had the engine compartment steam-cleaned a month ago, well before the problem started.

It's not just misbehaving while warming up. I can drive in 60s temps for a half-hour sometimes and still have it racing at 2200rpm. At other times, it runs completely correctly. Whatever it is is somewhat intermittent (e.g. works maybe 15% of the time).

I think next I should replace all sensors. So what is there --- O2 --- where is it located? What others -- temps?

BTW, it's getting about 40mpg -- not bad for a carbie.

[ricko1966]

A vacuum leak or intake leak can cause a high idle to much fuel will flood the engine not cause a high idle.I have a carb off of an engine right now if you want to callme shoot me a pm I ll send you my phone number and walk you through where the fast idle cam and adjustment are while I am holding a carb cause I don't have it memorized. I ll also walk you through chase ing vacuum leaks with propane. O2 sensors are the most over replaced sensor out there and they are so easy to test.I don't replace any sensor that can be tested without first testing it. Testing first saves time and money. Customers will not pay for parts and labor that don't fix the problem.