fast idle

[smokey]

help my 1988 420sel is idling at fast idle after the engine is warm but when the engine stands for a couple of minuites it returns to normal any ideas please

 

[smokey]

ah well

tickover is now 1400 even when warm any ideas how i check the idle control valve to see if its opperating as it should be

 

[Myros]

smokey

it is probably sticking. The easy way to be sure is swap it for a good one, but this will cost you the price of a good one to find out. Search the forum on "idle control valve". I'm sure someone posted up the various voltages etc and positions of the slide which could be expected from normal operation.

 

[Sarah123]

I think it is a vacuum leak. Maybe around your injectors

 

[Myros]

Good point by Sarah

you can check the injector leak easily by squirting lots of WD-40 type stuff at the injector seals where they sit into the manifold. If your problem vanishes, then new injector seals are what you need.

If not, carry on researching. A Clean of your throttle body plate thingy might be in order as well, just in case. Air filter off, clean lint free rag and just wipe the metal plate thet you have just revealed, and the walls of the body as well. Collected crud in there can mess with your idle as well. Make sure you get the angle between the plate and the body.

 

[Sarah123]

you can check the injector leak easily by squirting lots of WD-40 type stuff at the injector seals where they sit into the manifold. If your problem vanishes, then new injector seals are what you need.

If not, carry on researching. A Clean of your throttle body plate thingy might be in order as well, just in case. Air filter off, clean lint free rag and just wipe the metal plate thet you have just revealed, and the walls of the body as well. Collected crud in there can mess with your idle as well. Make sure you get the angle between the plate and the body.

Why thank you¬!

The little metal plate (horizontal?) isnt the throttle, its the airflow sensor. But its good advice about cleaning it - especially around the edges and in the conical cone that it runs in - because this can also affect idle speed (and the mixture setting is nearby). I think on these models the throttle valve plays no part in the idle, this is done by an air bypass with a screw adjustment somewhere nearby. This screw's grommet could be worn, though.

 

[television]

D and K injection

There are 3 parts to the system,
The throtle position switch tells the main ECU that the engine is at idle, and tells the idle control relay/ ECU to work, the idle control relay / ECU tells the idle control valve the correct RPM for idle.

The main ECU controls all above idle, if the idle system is not working, the fail safe is a very high idle most of the time. A dry joint in the idle control ECU can cause these problems. The swich for idle is either in the butterfly aperture(micro) or on the throtle cable.

Malcolm

 

[smokey]

thank you all but i found problem and hope it can help others,here goes:
tested the idle control valve with a home made 0 to 12 volt current adjuster made from old tv set this showed all was well i then examined the front of the unit and fond in the centre a threaded hole, what was this for?so i foun a bolt to fit this exactly and it proceeded to turn also it moved up and down so i pushed it down a little only a few microns and re inserted it to the engine and hey presto the tickover changed so i removed it again and adjusted it a few times and the tickover was fine but this small piston can still move i thought so i took a dot punch and tapped both sides to hold it after doing this i took the car to a tuner to test for mixture ect and all was well so if you have a high tickover try this first it may save you some money.
all the best to you all and a happy crimbo
Geoff