Woodsport Mk1 MR2 Manual Choke Conversion Kit
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 is with the waxstat idle valve. I’d say most mk1's 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.
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.
A new Waxstat valve from Toyota is over £180 and will still mean your cold idle will be way too high and for too long. My manual choke kit cures the problem for good and vastly improves the cold driving. The kit is supplied with full fitting instructions which can be done by anyone with very basic skills and hardly any tools.
Cure the bouncing or high idle for good!