Idle Issue--Up Down Up Down

ValleyHappy · Posted: Thu Mar 12, 2009 4:51 am Post subject: Idle Issue--Up Down Up Down

I have been dealing (or not) with my idle issue on my 87 for about a year or so now and figured it was time to get to the bottom of it. When I start my van I either get a good cold sart idle where the rpms sit at ~1500 and maintain a steady idle or I will get a start where idle cannot be maintained, as it wants to sit at 900 or so, and I have to apply gas to get it to hang it there until the motor gets warm. Regardless of how things start out, after 15 minutes of driving, my motor will start to cycle at idle. It will basically start at 1000 rpm or so and rise to 2500 over a period of 3 or 4 seconds then drop suddently back to 1000 or so and repeat the cycle. Up Up Up Down Up Up Up Down. I realize I could have multiple issues. My TempII is new, my O2 is not, and I have not tried adjusting the TPS. Wanted to post this just to get some feedback on where to start first.

Idle issues are commonly posted here but I wanted to see if the cycling characteristic lent itself to a specific component. I have read some responses in the search for a Digijet system but I wondered if the issue could be any different for the 2.1 system.

Thanks
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09 Suzuki SX-4 Crossover

ftp2leta · Posted: Thu Mar 12, 2009 5:50 am Post subject: Re: Idle Issue--Up Down Up Down

Dogpilot · Posted: Thu Mar 12, 2009 6:21 am Post subject:

Ben's write up is excellent. Two things I would add. Cycling is also a common side effect of a vacuum leak. The system will hunt to find the correct idle, cycling up and down its control range, but never finding homeostasis. The second item, unplug the Throttle Switch and gauge the effects. If you found and corrected the leak, unplugging the switch will let you find the mechanical bottom of the idle. Then you can, in your case, sounds like lowering the idle by screwing or unscrewing the big slot screw in the throttle body until you get a steady 850 rpms. Then plug the Throttle Switch back in and see how the idle computer system does in holding it (providing the switch works at about the right point).

If you have to adjust the switch, then search for one of the hundreds of times, just me personally, has posted the procedure. It is the most moody part of the van.
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Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

austinado16 · Posted: Thu Mar 12, 2009 7:43 am Post subject:

Replace that idle control unit and your problem will be fixed. It's a common failure.

Remember that O2 Sensors are not part of the cold start or cold running system, so you can always rule them out if your issue occurs during warmup.
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4 little pistons hammering themselves silly
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1970 Austin America
1966 Mercedes 250SE Coupe (sunroof & 4 on the floor)
1981 Volkswagen Rabbit Diesel LX P/u
1986 Kawasaki Ninja 600R
1990 GMC 1/2ton 4x4 Suburban
1995 Audi A6 Quattro Avant

ValleyHappy · Posted: Fri Mar 13, 2009 1:13 pm Post subject:

Well, after running around town today, I pulled the connector off the idle control valve as I sat parked with the motor on and cycling up and down. Settled down to a nice steady idle when I did. So what does this mean, other than it appears to be shot? Does this valve stay in the closed position when the plug is pulled? Is idle control only controlable from the idle screw once this valve is unplugged. I guess my question is with this thing unplugged, I may be fine and dandy and have a nice warm engine idle but have trouble when it is a cold start?
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09 Suzuki SX-4 Crossover

Dogpilot · Posted: Fri Mar 13, 2009 1:21 pm Post subject:

There are a couple of things going on there. The idle controller may have signal issues, the valve is responding slowly. So with the Throttle switch or the hall signal line unplugged, set the idle speed with the big screw on the throttle body (make sure there are no vacuum leaks, it will cause the system to hunt once engaged). Clean out the Idle Control Valve with carb cleaner. Check all the connections to the Idle Computer. If it persists, then you may be looking at a new Computer.

I would recommend doing the entire Idle Computer test as outlined in either the Bentley or the ProTraining books. I'd post a link, but the site hosting the material is having issues. You can get the books of my home page as well.
_________________
Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

ValleyHappy · Posted: Fri Mar 13, 2009 1:33 pm Post subject:

Thanks for the information Dogpilot! After I posted I realized the idle control unit could still be putting out a bad signal. Speaking of the idle control unit. I am not seeing it behind the right rear tailight, but there is a decent sized wire harness going into a black box behind the left tailight. Is this it?
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09 Suzuki SX-4 Crossover

Dogpilot · Posted: Fri Mar 13, 2009 1:45 pm Post subject:

Yes it looks like a double wide relay with a silver sticker on it. Be real careful prying it off its connector, they get very stiff with corrosion and the box plastic gets brittle with age. It should be attached to the bulkhead furthest away from the light hole.
_________________
Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G


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