1990 Cabby...just bought...idle goes up and down....

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todd@techt
Posts: 5
Joined: Sat Apr 25, 2009 11:00 pm
What year is your cabby?: 1990
Do you own a Cabriolet?: Yes

1990 Cabby...just bought...idle goes up and down....

Post by todd@techt »

So I just bought a 1990 Cabby and the idle goes up and down....drives fine....no misses....but the idle gets real low and then pops back up....sometimes stalls.

I read in the hayes manual it could be the EGR valve...or others have said O2 sensor.

Any place I would watch a video on how to replace these....or even a place where I could see these parts pointed out so I know what to change?

Any help would be great.

Thanks,
Todd
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Briano1234
Whats that smell?
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Re: 1990 Cabby...just bought...idle goes up and down....

Post by Briano1234 »

So I just bought a 1990 Cabby and the idle goes up and down....drives fine....no misses....but the idle gets real low and then pops back up

First Welcome to the TRF.

We are a friendly group of folks.

Let me start by giving you a few things...

1. Buy a Bentley, it is the bible for these cars.
2. Your Thread is worthless with out gratuitous pictures of your new ride.
3. Here is a web site that you really wnat to get to know. www.cabby-info.com

Now on to your question.

On the 1990 Cabby "which is Digifart" the highest suspect for a hunting idle is a vacuum leak.

Replace all the rubber vacuum hoses that you can find. There are only 2 sizes just go to a auto parts shop and get it in bulk, no more than 4 feet will be required.

The intake manifold can be loose, but that is a corner case issue.

To check for a leak, spray carb cleaner on all the hose connections. (including the large rubber hose from the airbox)

Another place is the Idle by-pass screw on the back of the throttle body .... it is a 7mm screw. (be careful here please) If the screw turns easily in your hand then the "o-ring" is bad. Counting the turns that you take to remove it, take it to your local "ace" or "tru-value" and get a replacement, wrap the threads of the screw with teflon tape about 3 wraps and re-insert it...

It could be a surging fuel pump, but I would bet on a vac leak.

There is also a Blue Sensor on the front of the head on a water flange, that is a CTS sensor, when it goes flakey it causes all kinds of grief so just replace it. It is available at NAPA.

That is all I can think of for now...... BUT Welcome to the TRF. Now postus pictures of thy ride... and a general location of the car would be nice as California cars are a different kind of digifant set up.
Briano

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
You can lead a user to a link, but you can't make him Click.... :screwy:
todd@techt
Posts: 5
Joined: Sat Apr 25, 2009 11:00 pm
What year is your cabby?: 1990
Do you own a Cabriolet?: Yes

Re: 1990 Cabby...just bought...idle goes up and down....

Post by todd@techt »

Ok so here are some pics. Ill just put in a new air filter, getting NGK plugs today, and changing out the CTS as well. Ill let you know how it goes. I checked the vacuum hoses, all seem ok.

O just hope its not the o2 sensor.....$150

What about the EGR?
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todd@techt
Posts: 5
Joined: Sat Apr 25, 2009 11:00 pm
What year is your cabby?: 1990
Do you own a Cabriolet?: Yes

Re: 1990 Cabby...just bought...idle goes up and down....

Post by todd@techt »

Ok so I did the CTS, plugs and air filter. Still no change...up and down idle. The I have looked at vacuum lines and they all seem ok.

Perhaps it is a fuel issue.
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Briano1234
Whats that smell?
Posts: 4105
Joined: Mon Mar 21, 2005 5:45 am
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Location: Duluth, Ga
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Re: 1990 Cabby...just bought...idle goes up and down....

Post by Briano1234 »

todd@techt wrote:Ok so I did the CTS, plugs and air filter. Still no change...up and down idle. The I have looked at vacuum lines and they all seem ok.

Perhaps it is a fuel issue.

Looks can be deceiving, just replace them. Then check the idle by-pass screw.
Briano

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
You can lead a user to a link, but you can't make him Click.... :screwy:
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gull
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Re: 1990 Cabby...just bought...idle goes up and down....

Post by gull »

An incorrect base idle setting can also do it, but you should make sure you have no vacuum leaks, first. The Bentley will have the correct procedure for setting the base idle. The dashboard tach isn't really accurate enough for this so you may also need a tach/dwell meter to really get it spot on.

The idle control circuit has a fairly narrow range of idle speeds where it works well. If it has to "prop up" the idle speed too much than you get surging as it hunts around.

The fuel system is the last place I'd look; if the car runs OK otherwise the fuel system is probably fine.
VW fan who fell to the Honda side of the force
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todd@techt
Posts: 5
Joined: Sat Apr 25, 2009 11:00 pm
What year is your cabby?: 1990
Do you own a Cabriolet?: Yes

Re: 1990 Cabby...just bought...idle goes up and down....

Post by todd@techt »

I removed the screw and the oring was good, but the tip was covered in gunk. I cleaned it up and screwed it back in. All the way in, it ran at first, but then didnt want to stay running. So I turned it out until I noticed that it increased the RPMs. I got it up to about 1200 by turning the screw out, and then I slowly turned it in until it started to idle at about 800 RPMs.

Im not sure what it is called, but the big round thing that comes off the top of the valve cover and is connected to the intake sits in the valve cover very loose. Im thinking that could be the issue. Is that suppose to have a seal on it? Mine does not. It just sits in the hole in the valve cover. My guess is that it should be air tight as well.

If you have any info on the oring or gasket size for that let me know.

Thanks,
Todd
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gull
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Re: 1990 Cabby...just bought...idle goes up and down....

Post by gull »

800 RPM may be a little on the low side. Check the sticker under the hood for the correct idle speed for your car. I have a CIS-Lambda car, so mine is probably different.

A loose valve cover breather could certainly create a vacuum leak that would aggravate your problem.
VW fan who fell to the Honda side of the force
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Briano1234
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Re: 1990 Cabby...just bought...idle goes up and down....

Post by Briano1234 »

Just below the 1000 rpm is a has mark @ 925 which is where I set all of mine.
Briano

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
You can lead a user to a link, but you can't make him Click.... :screwy:
sixsracing
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Re: 1990 Cabby...just bought...idle goes up and down....

Post by sixsracing »

First off, how much of a fluctuation is there? 100RPM's, or 1000's?

Does the idle air control valve (IAC) make a buzzing noise when the car
is idling?

Vacuum leaks are the biggest cause by far. The breather probably
isn't your main concern if the fluctuation is 500RPM's or more.

Check the full throttle enrichment micro switch on the throttle body.
There should be no resistance between the spade connectors at idle.
If there is then disconnect it and leave it, you don't need it anyway.

If the car is federal emissions then the EGR is a non-issue. Isn't one.

Ignition timing can cause a hunt.

A slightly rich mixture setting can also cause this. What color were the
plugs you took out? If they were black then you need to post back and
we can explore that route.

Keep us posted, there is little to no chance that somebody here can't help
you.
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todd@techt
Posts: 5
Joined: Sat Apr 25, 2009 11:00 pm
What year is your cabby?: 1990
Do you own a Cabriolet?: Yes

Re: 1990 Cabby...just bought...idle goes up and down....

Post by todd@techt »

Fuel pressure reg. ended up being faulty. Runs like a dream now. Just put in new clutch, motor mounts, brakes and dash rebuild. New top going on this weekend. 8)
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