87 TII, i have diagnosed my high idle (1250-1750) and have come up with the thermowax as the culprit. My car does the 3k warmup fine, drops down to 1500 and hangs there. If i drive the car a lot on a hot day eventually later in the day i might see 800-900 rpm idles, i imagine the temps under the hood get hot enough to finally expand the wax.

If i reach behind while the 1500rpm idle is happening and lift the fast idle cam, the car idles perfectly...

My question is, what exactly am i replacing (just the wax, the cam??), whats the part called, and how much is it usually?

Can i replace it without having to remove the entire throttle body?

Is there ANYTHING else that might be causing the thermowax not to expand?

 

Don't think so, unless the vacuum lines are suspect.

Might want to check throttle linkages as well. Could be pretty sticky ...that was my case not too long ago.

 

If it was throttle linkages i would think that me lifting the fast idle cam WOULDNT fix the problem, but it does. Since the car idles so well after me "removing" the thermowax from the equation i think everything else in the idle system is working properly.

i just got one through mazda for about 78 bux, should be here monday, how do i replace the damn thing?

 

The thermowax has a piston that extends and pushes against the linkage. The linkage can be adjusted to make the cam come off the rollpin.

You really have to download the Fuel section of the online fsm and take a look at it. There are pictures there. I ani't a gonna post 'em. The thermowax won't extend if there is no water flowing thru the throttle body or the passage in the throttle body is clogged with ???stuff.

It is most probable that you have found your problem. Don't buiy another thermowax. Clean the water passage and make sure the screws are adjusted. I'm betting on no flow of water thru the throttle body. See the fsm.

 

I did read the section and i did realize that i could adjust the fast idle screw. Thing is, how long is it supposed to take for the piston to extend and make the cam come off the rollpin. In my car, it never really happens (only sometimes, like i said, when ive been driving all day and i suspect the heat from under the hood does the trick). I remember in the other 2 rx7s ive owned cold warmup didnt last that long before it began to come down and finally rest at 750.

I guess, in any event, i should remove the throttle body and clean it up anyway... right?

 

Jpg attached. But it's a non turbo. Yours looks and works the same. IF It were me, I'd pull the intercooler off and try adjusting it with the screws.

A better understanding of it would be to remove the throttle body. With it cold, pour boiling water over the thermowax and watch its piston extend and the linkage move.

An idle that is slow to come down to 750 is likely to be a clogged water passage in the throttle body. The heat transfer from the engine is probably the only thing making your thermowax piston move.

In the scanned jpg: the redlines mean nothing to this post. The thermowax is the somewhat GOLD colored item to the right of the red lines. The red lines are the nipples for the vacuum and other hoses on the rear of the series four manifold.

Ooops. I noticed in the picture that there are THREE phillips screws that hold the thermowax on. And you can see the small piston at the bottom of the thermowax that is extended a bit, resting against the cam.

 

There is a way to prove its the thermowax. Some of us have gotten some plumbing pvc pipe from HomeDepot and installed it in lieu of the intercooler. What that does is let you do adjustments without taking the intercooler on and off and on and off and on and off.

You get pvc pipe the approx dia of the intercooler inlet hose and outlet hoses. I got a piece that fit the intercooler inlet hose. I cut it about a foot long and attached a ninty degree elbow to the other end. From that end I ran another piece of the pvc a foot or so to the throttle body inlet hose. You know, that ninty degree hose b/t the intercooler and the throttle body inlet. You have to use some imagination. You might have to block those two small hose that go to a series four intercooler.

With the pvc in place and the engine idling, you can reach under the throttle damper and lift up on part of the thermowax linkage and make it come off the cam. The idle should drop to a much lower idle. That iwll be the same idle that you'll get when the thermowax is adjusted to fall off the cam.

 

I jpg's the pvc stuff. It's a 1 1/2 inch elbow and 1 1/2 inch pipe. Those plumbers measure inside diameter so the actual outside dia on the pipe is something like 1.915 in dia. The short elbow on the end goes into my throttle inlet duct hose. It's a snug fit and I use no clamps. The other end of the pipe that is outside the scanner is straight. I had to grind and champer that end to fit into the intercooler inlet hose snuggly. No clamp there either. Cost had to be less than five to ten bucks.

 

Hailers,

First off thanks for all the help. I mentioned in my first post that i did exactly what you're referring to, only i didnt have to remove the intercooler.

I am able to reach my hand in and lift the linkage so it moves off the cam. The car then idles perfectly. I used the same logic you suggested to confirm my thermowax suspicion. Now im interested in replacing it.

Any noteworthy points of mention before i remove the throttle body? Anything i should be careful/aware of?

 

I had to replace this in my '91 NA a few years ago. It had obviously failed...the piston was fully extended, and there was 'crud' seeping out from it. While on the car, you might be able to see this part with a telescopic mirror, but it's pretty difficult to do on an NA even. Best thing to do is just remove the throttle body and a look. A quick visual inspection will tell you if it's shot - if the car was cool when you removed it, the piston should not be extended (only by about 1/4"). To test if it's working, remove it and just hold it under hot tap water. After a minute or so, the piston should start extending.

It's been awhile, but I think it takes a new thermo wax thingy (parts fiche just calls it "wax, thermo") and a gasket.

Oh, and don't forget to adjust your TPS afterwards - especially if you replace the "wax, thermo"

 

im having trouble getting the throttle body off... theres a bracket that holds the accelerator line and i cant get to the bottom bolt of the first section of the throttle body until i have that bracket out. But i cant get to the last bracket bolt unless i have the first section of the throttle body out... am i doing this in the wrong order, should the whole upper intake come out???

 

If you look at HAILERS pic of the throttle body above, the throttle cable hooks into that opening at the end. Just put some slack in the cable, and kind of push is back (towards the passenger side) until it unhooks. Then you can just slide it out of that bracket.

 

Another thing ive noticed (still having trouble getting the throttle body out so i put everything back together for today) is that the car runs INFINITELY better (read: power, and the boost gauge reads higher and the car pulls much harder) when the car is idling better, usually after the 2nd or 3rd start of the day when the engine and under the hood temps are normal. Could this all be related to the thermowax and the bad idle? Is this a closed/open loop issue?

 

Mmmmm...not really - at least not that I can think of. What usually happens is that the thermo-wax thing fails, the fast idle cam stay engaged, and then someone goes and sets the TPS to read idle in this condition. Only at idle, the throttle plates should be fully closed and in this situation, they are not. That certainly messes up the idle, but I'm not sure if it would mess up any other part of the throttle range - I don't think it would.

You might also want to check the action of the double-throttle diaphram. This is closed by vacuum when the engine is cold, then should open up when warm. If the solenoid that controls this isn't working right, it might be holding the double throttle butterflies closed.

 

Cant i remove those (double throttle butterflies) when i have the throttle body out, id like to leave the cold start items in like the thermowax because i dont want to sit there and hold my foot on the throttle during cold start...

any suggestions on getting the throttle body out?

 

I've got an NA, so I really can't help you with the specifics of removing the throttle body on your TII. On an NA, it often catches on the primary fuel rail, but a little bit of finesse is all it takes. Other than that, it's really pretty simple.

If you want to disable the double-throttle system, just remove the vacuum hose from the diaphram and plug it.