Following the installation of the fan bypass switch, detailed in the previous post, I took the car out for a 30 mile run. 16606 performed impeccably after which I put her back in the garage where she sat for the next two weeks. Then last weekend we had visitors from New York and they were excited to see and take a quick ride in the DeLorean. As I started to take the car out of the garage, I turned the ignition and nothing! It initially started but didn't maintain the revs at the usual idling position of about 900 rpm. I tried again, and again, the last time I pumped the accelerator and caught the revs enabling me to keep the engine going, but as soon as I released the pedal, the revs dropped to nothing and the engine naturally cut out. Needless to say, I had to abandon the joy-ride and my guests settled for photos with the car in the garage.
The following video demonstrates the problem. The first two attempts to start the car shows the instant failure to maintain the revs, the third attempt shows how I managed to catch the revs by pumping the accelerator pedal and hold them, but then once released, how the revs drop away and the car cuts out.
On Sunday I tried again but had the same results, no miraculous overnight resolution, so I knew I would need to reach out the the community for guidance.
I was informed that I should
check the electrical connection on the idle control valve
check the electrical connection on the micro switch on the throttle linkage
clean the connections on the above
check the electrical connections on the ECU behind the passenger seat
The above electrical connection checks needed to be performed with my multimeter with the ignition in position two.
To start with I had to locate these parts which I didn't know from Adam.
The red circles in the diagram of the Idle Speed Control System identify them.
28 - Idle Speed Control Valve Regulator Motor - Part 102502
15 - Microswitch - Part 102778
1 - Idle Speed ECU - Part 106896
I needed to understand a little more about what this part does so I turned to the technical workbook, it's relevant section is replicated below.
SYSTEM DESCRIPTION
The DeLorean Sports Car is equipped with a Bosch electronic idle speed control system. This system is used to maintain an extremely accurate engine idle speed under all operating conditions.
IDLE SPEED CONTROL PRINCIPLE
The control principle used is based on the fact that an electronic control unit (ECU) module is constantly monitoring the engine speed during an idle condition and correcting this speed when necessary.
The idle speed regulator contains a rotary valve which controls the air flow through a duct that by-passes the throttle plates. During engine warm-up, for example, the engine speed is reduced due to friction. The idle speed regulator will open allowing additional air flow to the engine, increasing the RPM to specification.
SYSTEM OPERATION
The idle speed regulator is constructed in a similar fashion to that of an electric motor. Its purpose is to control the position of a rotary valve mounted on its shaft. This valve controls the air flow through a duct that by-passes the throttle plates. The regulator is mounted on the left side of the intake manifold.
IDLE SPEED REGULATOR
The idle speed control system is only in operation when a microswitch (1) is closed by the throttle plates being in a fully closed position. This switch is located on the engine throttle linkage and allows the ECU module to operate. The ECU module senses engine speed from the tachometer and activates the idle speed regulator. The regulator changes the position of the rotary air valve in order to maintain a specified idle speed.
IDLE SPEED MICRO-SWITCH
At engine coolant temperatures below 15°C (59° F), a thermistor, located on the cool- ant distribution pipe, signals the ECU module to switch the regulator to a "wider" open position. This will increase the idle speed (fast idle) during the engine warm-up period.
THERMISTOR
IDLE SPEED CONTROL CIRCUIT
1 ECU module
2 Idle Speed Regulator
3 Thermistor
4 Idle Speed Diode
5 Idle Speed Micro-Switch
ELECTRICAL CIRCUIT FUNCTION
The ECU module (1) receives power through fuse #1 from the main relay when the ignition switch is in the "run" or "start" position.
When the throttle plates are fully closed, the micro-switch (5) provides ground for the ECU module to begin operation. An idle speed diode (4) is used to prevent "feed back" to the ECU module from another circuit which also uses the idle speed micro- switch to provide its ground.
A thermistor (3), located in the coolant system distribution pipe, will activate another circuit within the ECU module when the coolant temperature is below 15° C (59° F). This circuit will provide a fast idle condition.
The ECU module receives an RPM signal from coil terminal #1. When the engine idle speed is above or below specifications, the ECU module activates the electric motor in the idle speed regulator (2). The signal from the module will run the motor in a forward or reverse direction which will open or close the rotary valve as necessary to achieve proper engine idle speed.
Identifying the Components on the Wiring Schematic
In addition to understanding how these components work and interact with each other, I spent a little time trying to locate them on the wiring schematic, more specifically trying to locate the Idle Speed ECU. The reason for this, as I found out, is because the physical unit is split on the schematic but identified by its component number 108.
The extract from the wiring schematic below highlights within the grey zone, the majority of the idle speed related components, at least those that this post relates to. See below the image for a guide to the specific components highlighted.
Depending on the type/make of device you are reading this post on, you should be able to zoom in to the image by reverse-pinching in order to see particular detail
108 - Yellow - the ECU Module split into two schematic components
148 - Green - the Idle Speed Control Valve Regulator Motor
151 - Blue - Microswitch
For all of the following checks I needed to have the key in the ignition at position two.
First of all I checked fuse no. 1 in the fuse/relay compartment behind the passenger seat since this feeds power to these parts. There were no issues with the fuse, all in order and passed the correct voltage.
Second I located the Idle Speed Control Valve Regulator Motor, as seen in the following image.
I removed the connector from the top and tested it and received a steady 10v. I had been informed that with the power on as indicated (ignition position two) it should give off a gentle buzz or vibration when touched. I received no such feedback from the part so immediately my thoughts turned to this being the fault.
Third I checked the microswitch. I unscrewed the bracket to allow some movement and ease of assessing the part. I removed the two connectors (black and black/green wires) and tested with the multimeter. 7.65v received.
Fourth I checked the ECU behind the drivers seat which connects to the Idle Speed Control Valve Regulator Motor and the Microswitch. All connections seated well.
Fifth I went back around all these parts and checked the state of the connectors and cleaned where appropriate.
With the above five steps completed but knowing I was not getting any buzz or vibration from the Idle Speed Control Valve Regulator Motor, I set about attempting to start the engine again. As expected it did not work so I got on to DeLoreanGo.com to order a new
28 - Idle Speed Control Valve Regulator Motor - Part 102502
and to play safe a new 15 - Microswitch - Part 102778.
In true DeLoreanGo.com style the parts were ordered on Tuesday at just after 3pm and arrived with free shipping at 11:30am on Wednesday. Impeccable service, well packaged and a shed load of parcel tape. They even arrived before completing the first part of this blog post.
After work I went to the garage to start by replacing the 28 - Idle Speed Control Valve Regulator Motor - Part 102502.
I disconnected the connector from the motor -
Next was the job of removing the motor which starts with the bracket. The M6 bolt affixing the bracket to the air intake manifold closest to the cabin was blocked by the brackets tightening bolt which crosses it at almost 90 degrees, so to get to this first I had to loosen the tightening bolt as far as possible without removing it.
Now I was able to get to the M6 bolts that fix the bracket to the manifold. Using a socket extension made it easy to reach through the abundance of hoses.
With both bolts removed it was almost time to remove the motor. First however I needed to loosen the jubilee clip on the motor pipe hose, shown below, the clip has a red colour on it.
In order to remove the motor I additionally unplugged the connector to the cold start valve to help with access.
To remove the motor I agitated it back and forth until the hoses on either side loosened and I was able to remove them.
I slid the bracket off of the motor and set it aside for the time being.
The photo below shows the old (left) and the new (right) motor and in the middle the adhesive padding that comes with the new motor to aid grip and fit within the bracket.
The next photo shows the new motor with the padding affixed in the same position as seen on the old motor, shown above.
I fitted the bracket around the motor to check the fit which, due to the padding, was nice and snug and can be seen below.
I had to remove the bracket once more for ease of attaching the hoses to the bottom of the motor.
In the reverse order to how I explained the unscrewing of the M6 bolts, I fitted the bracket, tightened and secured it to the manifold.
Next came time to test the motor. I turned on the battery isolator switch, put the key in the ignition and turned to position two and went to the new motor to check for the buzz/vibration. Check out the video below.
You might need to turn the volume up but "It works! It works!". There is a buzz.
So the next thing to do was to start the car and see if it idles appropriately. The results can be seen in the next video.
Success!
Comments