Recently rebuilt my 1.6 M45 motor with MS1. Had it dyno'ed over the weekend and things went well in general. One issue that the tuner ran into was he wasn't back to get the idle to come down below about 2500 rpm's with the adjustment screw all the way down. TPS has been disconnected due to Megasquirt install.

He got around this problem, for now, by dropping the timing down to 0 at idle. This solution works for the idle while not moving but doesn't solve the other part of this. Everytime I rev the motor, the revs drop REALLY slowly to the point where it makes it difficult and jerky.

The tuner believes the throttle body is not closing all the way or is being impeded in some way. Therefore more air is getting into the motor when it shouldn't and the idle is raised and/or the revs hang.

He suggested taking the throttle body out, inspecting and also adjusting the stop screw on the throttle cam/bracket (whatever its called) to get the butterfly to close further.

Want to get your guys take on this. Does the tuner's suggestion sound appropriate? Are there other common issues? Am I missing something?

P.S. Did not have this issue previous to rebuild and the throttle body is the same. Only change was JB welding the set screws on the throttle shaft so they don't back out.

 

Check the cable for smoothness, go ahead and lube it, lube the spring. I've had similar problems like this on two cars and it was the cable on both occasions.

 

Will do. What do you think the chance the issue is the JB weld I put on there or the set screw for the throttle cam? Just want to go after the low hanging fruit first.

 

I had same issue and mine was cable related as well.

I read this once upon a time http://www.miata.net/garage/isc.html gave a little insight into idle.

 

Unless you jizzed jb all over the tb i don't think so.

 

+1, Hustler has extensive experience with lubing small, thin things.

 

Easy way to check if its the cable. Have someone push on the pedal while you watch the throttle cam. If the cam doesnt close and the cable goes slack the problem is in the tb or with the tb to cable connection. If the cam doesnt close and the cable stays taught then its the cable. If the throttle actually closes like normal then I'm going to bet that you need a tps hooked up in order to get the car into the idle maps and to otherwise run properly.

 

Will run these tests. Pretty sure the cable does not stay taught and that the cam will roll back to what looks to be the OEM position. Tuner thought that it might just not be closing far enough, therefore the suggestion to adjust the stop screw.

I was under the impression that the 1.6 TPS does not work properly with a MS because it isn't variable and is better left disconnected. Is this correct? Easy enough to connect the TPS if that will solve my issue.

 

The 1.6 TPS is either idle or not idle (or is it WOT or not WOT?). So the "stomp comp" tables dont work correctly. The correct way to do it is to run a real tps. The ghetto get you around for a couple weeks while you get a real tps in is to leave it plugged in an zero out all the transient throttle stuff. Atleast IMO.

 

So will plugging it in make any difference in my situation currently?

 

Here's a simple test:

Remove the end of the throttle cable from the pulley on the TB, start the car, manually rev it a bit, let go and observe.
If it still has a high idle, chances are it's not cable related. And vice versa...

Also, you can check for vacuum leaks with a smoke machine..
A vacuum leak, if sizeable, will render any idle adjustment moot.

While you are at it, remove the intake hose (or whatever) from the TB, and shoot liberal amounts of carb cleaner there. Use an old toothbrush to clean everything, then flush with more carb cleaner.
Start the car immediately afterwards, with the pedal floored (for clearflood purposes... You may take your foot off the pedal once the car fires up). Do not mind the initial black smoke, and rev the car gently till the smoke clears. That should clear up any weird deposits in front of, and around the butterfly.

 

Well it is pretty easy to just plug the tps in and try it.

 

Ok, finally got a chance to mess around with the car last night. I disassembled the throttle body and cable system, clean all with throttle body cleaner, checked for any interference with the JB weld I put on earlier and general seal of the butterfly valve, checked the throttle spring, checked the throttle cable motion and lubed the springs, shaft and cable the best I could.

What I found was that the throttle body doesn't seem to be gunked up in any way. The JB weld isn't the issue, only on the throttle shaft screws. The butterfly seals up very well, even throttle body cleaner was leaking past the seal slowly. The throttle spring moves smooth and freely. The recoil stops just before the stop screw and then uses the small shock to ease down on to the screw, looks like that's how it should operate.

The throttle cable does have some tension on it but since it's rerouted due to the supercharger it's always kind of been like that. I can remove the cable completely and try to lube up some more to see if that helps. I was using a dry lubricant at this time.

After putting everything back together the idle definitely came down. I hooked up my laptop and adjusted the timing back into the MS at idle. Idle came to about 1400 rpm's now with the screw all the way down. Drove the car around, revs definitely drop down quicker now. Now I am having some inconsistent idle issues though. If I rev the motor, sometimes it will come back and idle at 1400 or sometimes in almost wants to die out (bogging).

I think I want to test for vacuum leaks next. You guys have any other ideas? Still think its the throttle cable? Maybe settings on the MS?

 

Bad cell phone pics of the throttle body and IACV

 

A little off topic, but I would feel a little uncomfortable putting anything on the throttle shaft in an attempt to retain the screws in event of failure. Miata engines are little harmonic making machines, especially if redline in raised. JB Weld is pretty amazing stuff, but what is the chance of it cracking and breaking off? There is a much better solution out there, to be sure, more expensive than JB Weld, but cheap compared to replacing a engine.

 

Your picture doesnt look like a skunk 2 tb. The point of the JB weld is so that when the throttle shaft eventually does break most of the pieces wont make it into the engine.

 

Would feel better with an aftermarket throttle body as well but not in the cards for budget reasons right now. Also with the supercharger is in the way between TB and motor, that should chew up any bits pretty well

Then I can go turbo!

 

Just concerned that the JB Weld might beat the throttle shaft/screws to the punch. The pics are of the tb off my fp car, stock tb, custom shaft, epoxy butterfly, and blade shaft end to accept a 99 tps

 

Are the water lines on the TB always capped off or you just have them capped to keep water from dripping when you work on it?

 

Water lines are capped on the IACV. I have removed the air valve at the side of the intake manifold as well. This is all in conjunction with doing the coolant reroute and removing the front water outlet neck.