For quite a few years now I’ve had countless MK1s
coming to the garage with the same old problems. They all seem to be prone to
the same fault sooner or later at some time in their life. We are all aware of
the infamous 5th gear popping out on post 120,000 mile cars and drop link
failure from 60,000+. However one aspect of MK1 troubles has escaped any real
attempt to cure the problem, and that’s the cold start waxstat valve syndrome as
I call it. I’d say one in 4 MK1s I see have a problem with this valve, for those
of you who are unaware of its function it keeps the idle high on the engine
during starting until the engine has warmed up. This however raises a few
problems and far be it for me to criticize the design of our beloved cars I’m
afraid Toyota didn’t quite get it right when it came to the cold start system.
The problem lies in quite a few layers, one of which is the annoyance that even
if you have a fully functioning waxstat valve with no problems at all it seems
to take forever (especially during the colder months) for the idle to return to
normal after starting. Indeed I’ve noticed on many occasions that it sometimes
takes up to 3 miles of driving before it settles to 900rpm. Many of you won’t be
aware that there is in fact no need for the waxstat valve to stay open this long
and in fact a few hundred yards of driving or 60 seconds of idling sees it
capable of doing without the choke. This in turn means that for an extra 2 miles
or so the engine is drawing in more air than it needs and in addition is being
supplied with the extra fuel to compensate…not good for our fuel economy!
The waxstat basically allows extra air to be drawn past the throttle to
simulate throttle being applied when the engine is cold, the map sensor informs
the ECU that this extra air requires fuel and that’s our choke. The second
waxstat problem is that frequently they stick open, that is, even though the
engine has reached running temperature there’s still an extra amount of air
leaking past the throttle and the ECU allows more fuel for that. However the ECU
is now being told by the throttle position sensor that the throttle is shut, so
on the one hand its being told I have the throttle open (the air leak) please
give me fuel, and on the other hand the TPS says throttle shut reduce fuel and
the end result is a surging idle as the ECU battles in conflict between the
sensors. I’m sure at one time or another we have all witnessed this surging idle
when the cooling system has become air locked or the waxstat has stuck open. Ok
that’s the problem fully explained and I started research work into a solution
to the problem over a year ago.
It occurred to me that the system we have got is all fine and dandy if you
live in Japan, nice hot days when the engine gets up to temp straight away and
indeed this is the climate that this system was designed for. It seems the that
UK spec cars were ignored in respect of the climate we have to endure for 8
months of the year! So a little bit of retro thinking was called for, remember
the days of old Morris Minors, Minis and even old Fords when it was a joy to
turn the choke off as soon as things got going? Indeed things all seemed to go
pear shaped shortly after that with the introduction of automatic chokes
appearing for every make and model. Countless complaints of dreadful fuel
economy ravaged through the motor trade and even today it seems many cars, even
with advanced electronic fuel management systems, still suffer from over
fuelling during cold start. I enquired about the cost of a new waxstat valve
from Toyota…£140! and at the end of the day it still has the inherent problem of
staying on for far too long. So a cheap manual choke conversion was clearly the
answer. Not some pull out cable operated affair like in the good old days (I’m
nearly sounding as old as Mr. Jones!) but a simple dash mounted switch that can
be flicked on or off to control the cold start. After much toying with the
throttle body on a MK1 I found that Toyota weren’t such idiots after all and
they have conveniently supplied an extra air pipe on the throttle body that I
could use for my own system. Indeed I found I could leave all of the original
Toyota waxstat system in situ and not even remove a single piece of it, which is
good news for the MK1 purists among us. The system I came up with is merely an
“add on” which can be removed from the engine at any time with no side effects.
The standard waxstat is simply disabled by blocking off its auxiliary air supply
with a plastic tyre valve cap, indeed many of you will be aware of this mod as a
cheap fix for a waxstat that has given up permanently. The manual system
consists of a 12v switching air solenoid that plumbs directly to the throttle
body and feeds from filtered air on the air filter piping, there’s no holes to
drill and no modifications need to be made to the standard set up. A simple
wiring consisting of one wire to the battery + and another wire running forward
to the dashboard onto a switch is all that’s required to make this work. It took
me many months of searching for the right solenoid valve to come up with one
with the correct flow rate for the job. Below is a pic of the valve and piping
in situ on a MK1.
The switch is mounted in the blank right beside the “coin holder” to the left
of the steering wheel and it lights up bright orange when the choke is switched
on.
Many of you who actually know me will know that the things I do for the MK1
community are not based on personal gain, my garage business sees to that side
of things and these little projects that I undertake are purely to progress
forward in helping MK1 owners get the best out of our cars, plus I like the
challenge of it! So this isn’t some get rich scheme or wacky “ecotek” valve
that’s nothing more than an automotive sugar pill in my opinion, this genuinely
works as a manual choke conversion with a bonus side effect of reducing fuel
consumption. It has to be added that the system will have absolutely no effect
on hot running fuel economy and the fuel economy you got before the system was
fitted will remain the same, however it’s during cold start where the saving is
made. I’ve fitted several of these kits to members MK1s since completion of the
design and posted a few throughout the UK. So far I’ve had very positive
feedback about its function and it seems it does exactly what it says on the
tin! If you are currently having a problem with your waxstat valve or even if
you want to be able to control the choke yourself then this is the solution.
Cost of the kit with full fitting instructions is £65 plus £5 p+p anywhere in
the UK. I’ve found that the cost of the kit can be redeemed in saved fuel in
under 6 months of average mileage. If you have any queries about the kit please
get in touch and I will be happy to answer. paulwoods.v6mr2@ukf.net
PAUL WOODS
