[DML] idle problems

["Warren Wallingford" <warren@xxxxxxxxxx>]

The flurry of talk lately about idle control problems, especially unwanted high idle, mirrors calls we get for help from people working on their cars.  The following is a functional approach to isolating problems that result in a high idle.

Idle speed in a Delorean is electronically controlled.  When everything is working correctly, the engine will idle at 775 rpm regardless of load or temperature.  The conditions that result in a closed-loop, regulated idle are:
1) Closed throttle plates
2) Operated; ie, 'clicked', idle microswitch
3)  A sealed intake-no vacuum leaks
4) Functional Idle Control Motor, Idle ECU, and Vacuum Solenoid

To insure that the butterflies are closed, check for mechanical binds or maladjustments in the linkage.  Disconnect the bar between the throttle spool and the lever on the throttle shaft.  If this fixes the idle, readjust the length of the cable or the bar.

With the plate closing properly, adjust the screws on the lever so that the microswitch operates just as the plates close.  Use the other screw to provide a positive stop for the lever.  The microswitch does two things: It signals the idle ECU to go to work and, using the vacuum solenoid, takes the vacuum away from the distributor.  You can check this manually at the distributor diaphram.  

To check the idle motor, grab it with the key on.  If it's vibrating, generally it's OK or will be. Spray some WD-40 into the throat and give it a couple of firm raps with the tuning hammer. If it's not humming, check the connection on top.  Peel back the boot to see that none of the little connectors have backed up into the boot.  If by this time, the motor doesn't respond, you're in for an idle ECU.  Also, there is a temp sensor that tells the ECU to let more air in when the engine is cold-the Contant Idle Switch or Thermister.  These go bad in a characteristic way.  The engine will idle fine until it warms up, then as the engine warms, will rev higher until it settles into a 2000-2500 rpm idle.  The thermister is located in the coolant distrubution pipe under the intake manifold.  It cannot be unplugged or overridden exept by disabling the ECU.  This failure is very irritating.

After all this, if the idle won't be controlled, there is surely extra air coming from somewhere.  Find it.

Pictures for the idle motor, ECU, Solenoid and Thermister are behind the links.

http://www.usadmc.com/dmcstore/ViewPart.asp?PID=801&Qty=1&ShowCart=true
http://www.usadmc.com/dmcstore/ViewPart.asp?PID=1776&Qty=1&ShowCart=true
http://www.usadmc.com/dmcstore/ViewPart.asp?PID=362&Qty=1&ShowCart=true
http://www.usadmc.com/dmcstore/ViewPart.asp?PID=795&Qty=1&ShowCart=true

Warren Wallingford
DeLorean Motor Company (Texas)
15023 Eddie Drive
Humble, Texas 77396 USA

http://www.delorean.com
800/USA-DMC1
281/441-2537
281/441-2813 Fax

[Non-text portions of this message have been removed]






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