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High Idle Speed 5000/200 models


On my previous 86 5000CS Turbo and on my newly purchased 1989 200 TQ I had an intermittent idle 
speed problem that drove me nuts for awhile. The car would randomly have an idle speed anywhere from 
1000-2500 RPM on deceleration and also after coming to a stop. It gave new meaning to Un-intended 

Here is what I finally found on both of these cars. The idle/full throttle switch mounted on the throttle 
shaft had an intermittent connection inside where the idle micro switch connections are soldered to the 
housing. In both cases when I measured the idle switch resistance with an ohm meter, it varied from 10 
Ohms all the way up to 5-10K ohms. One minute the switch showed it was ok, and the next minute it had 
a high resistance. The resistance should be pretty low (a few ohms) when functioning correctly. 

The switch can be taken apart by carefully cutting the cover off with an exacto knife. Then the 
connections can be resoldered. You can also clean the contacts on the Full throttle switch and resolder its 
connections while you have it opened up. I glued the cover back on using some black silicone sealer. This 
fixed the intermittent high idle problem and the light surging I was experiencing under deceleration while 
in gear.

I also took apart the micro-switch inside but I don't recommend this unless you are a practicing 
neuro-surgeon. The micro-switch innards are very tiny and tend to fly away when the switch is opened 
up. Some electronic parts stores carry replacement micro-switches that may fit inside this housing.
Hope this helps.
Scott M.

>On Wed, 24 Jan 1996, Ted Blank wrote:

> Hello friends,
> I am losing the battle to stem the deterioration of my much-loved 875KTQ.
> Here are the challanges I am facing right now.
> 1.  High, sometimes pulsing idle.  I've cleaned the idle stablizer with no
> significant effect.  Should I replace this item or look elsewhere (O2 sensor
> maybe)