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
#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.
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
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
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.
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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