Engine Idle Discussions

Created: 8/16/03

Last updated: 

Author/source: DML

From: <dherv10@aol.com>
To: <dmcnews@yahoogroups.com>
Sent: Monday, May 27, 2002 9:37 AM
Subject: Re: [DML] idle speed Adjustment

Group, This is what I do.
Most of the time what I see is wrong with fast Idle is the adjustments. You
must make sure you don't have any vacuum leaks.
#1. As David mentioned earlier, the air horn gaskets. Very often these are
not replaced.
#2. The idle speed motor tube into the lower parts of the air flow meter
isn't sealed properly.
Once the vacuum leaks are stabilized, the adjustment arm under the cable
spindle must be properly adjusted as to allow the throttle plate lever to go
all the way down. You may have to remove the Air horn to verify this or just
unhook the arm and see where the lever rest at. Make sure the lower
adjustment screw isn't keeping the lever from going all the way down. One you
have determined the throttle body lever is all the way down and the arm is
off, then turn the lower adjustment screw about 1/4 turn clock to get it
right off the bottom. (Rest Screw). Now adjust the upper screw in or turn
clock to trip the micro switch about 30 thousands. This can be the starting
point. Reattach the lower arm and make sure you adjust it as to allow the
lever to stay in the rest position. You may also have to adjust out any slack
to looseness on the ball connection on the lever. I took mine off and
soldered the ball joint because it had become so loose I couldn't get my idle
to stabilize. Also refer to D:05:02 in the work shop manual for the
thermistor and ECU info.
John Hervey

From: "checksix3" <checksix3@juno.com>
To: <dmcnews@yahoogroups.com>
Sent: Monday, May 27, 2002 12:36 PM
Subject: Idle speed problems
Did you get this solved? Shouldn't be too difficult, its likely
mechanical binding, misadjustment, or electronic.
One at a time:
>>>>i adjusted the spring on the throttle one more notch.  it's
pretty tight now (i think mine was already adjusted forward).  i also
adjusted the throttle linkage.  right now it is all set up so that if
i have the pedal to the floor, the throttle hits the full throttle
switch, and when i let the pedal all the way back down, it is pushing
on the idle speed switch w/o any additional play on the switch.<<<
Be sure that when it hits the idle switch the throttle plates are
completely closed. Adjust that *first*, then set the idle switch.
When you are done, be asolutely sure there is no mechanical binding
in the system.
>>  when i have a screwdriver pushed down on the idle speed switch,
my idle screw is adjusted so that i am running at about 800 rpm or
so.  STILL, when i put my foot on the gas and let the pedal back
down, the idle doesn't kick down!!!  it sits at about 1200 RPM. 
however if the car is at say a stop sign, i can hit the gas with my
foot on the clutch and let it drop down fast, and THEN it will kick
down.  i can't find any mechanical reason why is should be like
this.  i would think the switch doesn't care if it is tripped hard or
softly - it is still being tripped.<<<
It doesn't care if tripped hard or softly, its just a contact
closure. After being sure the throttle plates are closed (using the
other adjustment screw nearby), set the idle switch screw to depress
the idle switch only enough to close it. You should still be able to
reach in there and push it more after it clicks. You don't want it
to "bottom" out, ony actuate. Bottoming it out will stress the
actuator attachment point. (Air cleaner is off to do this.) From what
you're saying, it appears your ISC systems is working and you have
binding or other issues.

>>>1.  how far into the idle speed switch is too much?  should the
screw be pushing on the switch all of the way, medium, or just enough
to take the tab off the switch?<<<
see above, just enough to close the switch.

>>>2.  basically every adjustment you make throws something else
off.  how do i set up the linkage so that when the pedal is fully
depressed i know that the throttle butterflies are wide open?<<<
Your problem is idle. We can worry about making full throttle and the
WOT enrichment switch after you fix the idle. Forget about it at this
point. (The WOT switch is not connected to the ISC system.)
>>>3.  the shop manual says that the idle ECU recieves a ground when
the butterflies are fully closed.  if my butterflies are off, perhaps
my ECU isn't recieving a ground all of the time unless i let the gas
off quickly, maybe hitting the butterflies hard and making it all
work? just a theory.  how do i test it?<<< 4.  how do i know if my
idle speed motor is working?  under which conditions  should which
things happen.  i'm not proficient with a DVOM so if anyone has
any ideas, they will have to tell me how to hook everything up.<<<<

The idle switch basically "wakes up" the idle ECU by powering it.
The ECU has no ground point other than the switch, so its dead until
the switch is made. Can you use an ohm meter to measure the switch
closing? You can also use a voltmeter and it would be easier if you
knew how to do this. If not, here are two ways to test most of the
ISC system:
1) when the car is warm and idling, disconncet the idle switch. The
idle should increase. 2) With the car idling, grasp the throttle
spool and increase throttle only enough to lift off the idle switch
tab. Holding this position (about 1000-1200 RPM), use a screwedriver
to depress the idle switch actuator tab back down. Idle should
decrease. If either of these happens, its pretty much working.

>>>is there something else i'm missing? i'm inclined to believe my
butterflies are part of the problem.  i really need someone to guide
me through complete adjustment of the throttle system.<<<
What you want is this: 1) throttle plates fuly closed. 2) Idle
switch "made" just enough to close it. The throttle stop screw is on
the plate, the idle switch screw is just depressing the switch tab
enough to actuate it. 3) No mechanical binding. Look inside the
throttle spool. The spring bends around the center pivot post. It
must not touch the post, only curve around it. If it touches, unhook
it and bend it so that is does not touch the center post. If the idle
switch is made everytime you you release the throttle, you have no
binding and this is not your problem.

To set it up from scratch:

1)Loosen both lock nuts on the throttle stop screw and the idle speed
switch screw and back the screws way off.
2) Disconnect the throttle linkage and allow the throttle plates to
close. Maybe disconnect the accel cable also.
3) To be sure they are closed, gently push on the ball attached to
the throttle plate linkage. You should see no more movement. If you
want to know for sure, you'll have to remove the pipe and eyeball
4)  Make sure the throttle spool is all the way back. Have some
slight slack in the cable. Make sure everything is all the way back
and nothing (throttle screw, idle screw,  auto trans cable,
accelerator cable, etc) is holding the throttle plates open. Be sure
the entire thing is at "rest".  Check for binding in the throttle
plates *and* the cables, spool, etc. Now is a good time to check for
binding because you have the linkage connecting the two seperated. If
all is OK, sdjust throttle linkage to fit and install it.
 5) Turn throttle stop screw in until it just contacts the stop
plate. Watch it closely until it *just* starts to move the linkage.
(starts to open the throttle plates) Lock it in this position.
6) Adjust the idle speed switch screw to just actuate the switch.
(not touch it, but actuate it). Lock it in this position. Slightly
open the trottle by grasping the spool. Make sure the idle switch
clicks open. Release the spool and makes sure it clicks closed. Put
an ohm meter on the switch (after disconnecting the wires if you
wish, or at the ECU connector) to be sure it is opening and closing.
The throttle stop screw should contact the plate just after the idle
switch closes (or almost at the same time) with the throttle plates
closed. Bascially, the throttles and idle switch should be closed
with their stop screws taking the "load" so they are not forced
further closed by the linkage.
You likely have either binding or electrical problems. I'm betting
binding. Look inside at the spool return spring, I've seen that cause
binding before.
Want to remove the idle speed function for testing purposes?
You need to "break open" the feedback closed loop and go to manual
idle. (No need to do this if the ISC system test I mentioned above
checks out.)
1) Either unplug the idle speed motor, one wire off the switch or
unplug the idle speed module behind the drivers seat.
This will "fix" the ISC valve at whatever position it happens to be
in. (Its a rotary valve, kinda like a stepping motor.)
2) Remove the idle speed valve and plug both hoses or leave it
installed and pinch off or plugged the hose that leaves the idle
speed valve and goes to the manifold. Either hose will do, the one
towards the rear of the car is easier to get at. (Best to remove the
motor and plug both of them, pinching hoses is for Neanderthals.)
3) Open the idle adjustment screw on the manifold a few turns and
start the car. Make sure you're adjusting the idle speed and not the
air balance screws. See your manual. Warm the car up and set the idle
to about 800 to 1000 rpm. Doesn't matter, this is for testing.
You now control the idle using only this screw to let air into the
manifold. You now have "open loop" idle control. Manipulate the
throttle. If the idle consistantly recovers to *about* what you set
it at, then the problem is in the idle speed system (motor, switch,
ECU or wiring) If it *still* is not repeatable, check for binding or
problems in the linkages or cable. (If you have an auto transmision,
don't forget the govenor cable.) I suspect a throttle spool spring
touching the center post as described above. If it is touching,
correct that and put the spring back from the one notch you moved it.
Also lubricate the spool while you're in there.

Electrical problems could be as follows:

1) Bad ECU
2) Bad wiring
3) Bad idle switch
4) Bad cold idle thermistor.

There is a thermistor that monitors the coolant temp. It results in a
fast idle when the engine is cold (below 59F, as I recall). Btw, I
manipulate this circuit to idle up my car when the AC, headlights, or
fans are on. I have an adjustable pot so I can select the high idle,
it doesn't effect the cold idle setting.

This thermistor could be bad, but I doubt it. Other items to check are
CO adjustment (is the plug there?), idle and air balance screws (all
three should be closed) and binding in the air balance plate or
control plunger. With the car off, remove the air filter housing and
gently push down on the plate and see if it returns to the same
position. You will lose your fuel system resting pressure and flood
the engine some (may be hard to start immediately thereafter) so
don't do this too many times. (I doubt this is the problem however.)
Does the idle hunt when cold? This common problem is most often
caused by slight misadjustment of the CO setting.

You could have some weird problem, such as a funny tach signal. (Its
the "process variable" in the ISC system, what you're actually trying
to control) but I doubt it. At anyrate, its always best to open any
feedback loop to troubleshoot it.

Some time spent with an ohm meter/voltmeter at the ECU connector will
tell you if the sensors and wiring are OK. Let me know and I'll walk
you through it. Opening the idle speed feedback loop will tell you
alot, its difficult to troubleshoot closed loop systems as, if not
set up correctly, they tend to oscillate as they chase the setpoint.

All this should reveal the source of the problem and you can go from
there. After you get this figured out you can check the WOT
enrichment and auto trans kickdown (if you have one) switch settings.
Let me know and I'll offer more help if needed.
Good luck,

From: "mgutkowski@cix.co.uk" <webmaster@delorean.co.uk>
To: <dmcnews@yahoogroups.com>
Sent: Friday, November 15, 2002 6:40 AM
Subject: Setting Fuelling - Why does the DMC PRV Hunt? [long]

Hi All

Bit of a lengthy one this. Let me set the scene.

I've bought a new project car, VIN#4426 from Germany. It needs a new
engine. As you are aware, the PRV was used extensively over here by all
three manufacturers and a couple more besides.

By an extraordinary stroke of luck, I was put in touch with a guy by the
name of Darren Bowker who hails from Manchester. Not only is he a mad keen
Renault fanatic (and owns a concours Renault 30), but he has built several
PRV's from scratch before, and was more than happy to take on the work of
building me my new one. I even had the option of a performance version in
the 200-210hp range...

(some might ask "why not buy a new crate engine from Houston?", and the
simple answer is that it'll be far cheaper to have Darren build me one)

Anyway, at the NEC last weekend, I finally got to meet him, after numerous
e-mails and phone calls, and gave him the lump that had come out of #4426
(which came from a carbourettored Peugeot 504 circa late 70s, with a 2664cc
PRV). This engine had never run in the DeLorean and was merely a block and
heads by the time I got to it.

I had decided that I wanted a completely stock DMC engine, and this gave
Darren the task of establishing exactly what parts cross-reffed to what
version of the engine, and more importantly, how to set up the lambda and
idlespeed systems which are not used on the engines he has built before.
For interests's sake, you might like to know that the DMC PRV uses a
Renault sandwich plate and sump (although the Renault sump was not
aluminium and Darren was quite jealous about this) but uses Volvo pistons &
liners, crank, heads, cams, intake manifold and injection. The block is 99%
identical across all PRVs of this age.

One of my choices sometime ago was whether to stick with the DeLorean's
"over complicated" idlespeed system. My decision was based in part on the
archetypal "hunting" of a DeLorean engine when cold, and I told Darren
this. He thought I was being daft and that "there must be something wrong
with a lot of DMC engines then" until he heard Chris Parnham's 111-mile,
museum stored car doing it. We also worked though how to set up the
idlespeed system, and how the DeLorean manual tells you not to adjust the
setting screws - they're meant for the older Renault system (the later
R25's used the idlespeed system found in the DeLorean, but don't hunt
either according to Darren). This is the e-mail I got from him this
morning. It should make interesting reading:
Went to see the font of all PRV injection knowledge yesterday, Steve
Whitehead and learnt all about setting up lambda K-jet. He also leant me
the manual that shows you how to do it. It appears that DMC didn't want
unskilled people messing with the settings but Renault had no proplems with
giving the dealers the info to set them up. To set the idle you clamp off
the pipe to the idle valve and set it with the brass screws as per engines
without idle system,ie remove and clean the screws,refit them and screw
them all the way in.Back off the two front ones 2 turns and the set the
idle with the back screw to 900 rpm. It is absolutely critical that the
control pressure is correct (3.4 bar) and that the pressure from the pump
is correct(4.8-5.2 bar). The only thing you can't do on the DMC is set the
co which should be 0.7-1.0 before the cat. The idle should not vary when
cold and the manual gives all the testing proceedures and values of
electrical sensors etc.

What was interesting was the crude manner in which the lambda system
operates! All it does is vary the fuel pressure in the lower chamber of the
metering head with an oscillating valve to weaken the mixture if the lambda
sensor senses the mixture is too rich. Simple. If yours runs better with
the lambda system on, then it is running too rich when the lambda is off
[#1458 stops hunting when the lambda system cuts in - Martin], so either
the control pressure is too low, the pump output pressure is too low or the
mixture is out of adjustment. A way to set the mixture screw with out a co
meter is to bridge the fuel pump relay with the engine off,pull out an
injector and put it into a container and put a washer (about 0.5mm-1.0 mm
thick)under the air plate stop to hold it in the same position as at idle
and turn the mixture screw untill the injector "cracks" which is the point
at which the injector starts to spray.Then set the idle and robert is your
fathers brother!

I've already learnt to respect Darren's knowledge, so wanted to clarify the
"hunting" of the DeLorean engine - why does it do this when it apparently


From: "mgutkowski@cix.co.uk
To: <dmcnews@yahoogroups.com>; 
Sent: Monday, November 25, 2002 7:10 AM
Subject: PRV Hunting - response.

Hi All

Here's a collection of points written by Darren in response to mails I
forwarded to him off the DML, and general chatting with regards the PRV
hunting. There's some other info in there about how to set up the fuelling,
and also a reply to Bill identifying his engine. I hope it's interesting
and not _too_ long.



My opinions will probably keep the guys across the pond "cussing" for ages!
At the end of the day I know what works and when I build an engine it has
to run perfectly, and they always do, or else a running fault could cause
premature wear of the new engine (probably the reason the engine wore out
in the first place). Many of these guys with opinions have cars that
hunt......That is the case for the defence your Honour :-) Shain makes the
most sense. I am beginning to believe it is a problem with vacuum leaks;
perhaps we are getting too deeply into the fault and it is nothing more
than 20yr old rubber O rings are no longer sealing properly when cold. I
know that when I strip a PRV the inlet manifold O rings are squashed and
turned from rubber to hard plastic.

To the guy who suggests disregarding the Renault manual; the Renault k-jet
manual is written by Bosch and it does cover Lambda vehicles (Switzerland)
as it is written for european vehicles but I can see how he comes up with
that idea not having seen the Renault manual.

There is no way a variation in cylinder pressures or spark plug variations
would cause an engine to hunt, in fact one running on 5 cyls would not
hunt, it would idle slower which would then be corrected by the idle valve
and then held steady by the valve if set up correctly. I suspect that even
someone who has been working on DMC's for years would not know the correct
setting proceedure as it is not in the DMC manual and they would be
unlikely to get hold of a Renault manual as Renaults are not sold in the US.

It appears that DMC didn't want unskilled people messing with the settings
but Renault had no proplems with giving the dealers the info to set them
up. To set the idle you clamp off the pipe to the idle valve and set it
with the brass screws as per engines without idle system, ie remove and
clean the screws, refit them and screw them all the way in. Back off the
two front ones 2 turns and then set the idle with the back screw to 900
rpm. It is absolutely critical that the control pressure is correct (3.4
bar) and that the pressure from the pump is correct (4.8-5.2 bar). The only
thing you can't do on the DMC is set the co which should be 0.7-1.0 before
the cat. The idle should not vary when cold and the manual gives all the
testing proceedures and values of electrical sensors etc.

A simple way to set the mixture screw with out a co meter is to bridge the
fuel pump relay with the engine off, pull out an injector and put it into a
container and put a washer (about 0.5mm-1.0 mm thick) under the air plate
stop to hold it in the same position as at idle and turn the mixture screw
untill the injector "cracks" which is the point at which the injector
starts to spray. Then set the idle...

The K-jet system will handle more than 140 hp,the standard Volvo 760 is 170
hp in european spec without cats. The Renault 5 Turbo 2 (mid engined) used
the PRV metering head and produced upto 350hp from 1400cc in tarmac rally
spec! I also used to prepare a Golf GTi 1.8 with K-jet that put out 190hp,
although the idle had to be set at 2000rpm because at low speed the pulses
that came back up the inlet manifold upset the flow plate, that is the only
problem with k-jet when the cams get wild. The pulses push the flap shut as
the pulses going in are trying to push it open when you run cams with alot
of valve overlap resulting in no air movement which equals no or very poor
idle. Obviously the active idle speed valve was not designed to operate
with toblerone shaped cams with big overlap, it was designed to give a
steady idle dependent of engine load with standard cams.


(Bill's engine)

Ah, The Renault 30TX is alive and well and living in a DMC! The injection
system Bill describes is Phase 2 R30TX. I have actually got a factory
bulletin from Renault advising how to retro-fit this system to a phase 1
30tx that has running faults (phase 1 had the same as DMC). The metering
head is alloy, not cast iron, the fuel lines are solid steel pipe and it
has a conventional fuel pressure reg as well as a k-jet pressure reg to
improve throttle response. As to a lack of power, it should produce more
power, as in the Renault it gives 144bhp from a 2664cc PRV. The lack of
power could be down to the distributor not giving enough advance if it has
a DMC dizzy.If he wants a Renault dizzy I have them in stock, but he needs
to get the advance checked first. The supplied engine number for Bill show
140 which is a Renault 30TX engine out of a phase 2. It may lack torque off
the line as it is only 2664cc! Sounds like he needs an engine building to

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