Stock cruise control with boost help.
 

So my car has a problem with cruising with the control on. Mainly if the car has to increase load for a small hill or something is will go from 10vac to 0-3psi for a split second then back off to cut power. Will do this over and over until i turn off CC and rest after the road is flat again.

From outside/inside the car it looks, feels, and sounds like i'm stomping the peddle to 50% then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting then stomping then lifting.... you get the idle.

You taught your car how to curse?

But seriously... you might try putting a vacuum check valve inline between the CC actuator and the vacuum source. Might need a vacuum storage tank too. Sounds to me like it loses vacuum under boost, then it starts cycling as it regains vacuum momentarily, then loses it, then regains it, then loses it, then regains it, then loses it, until you finally give up and kill the cruise.

Did the MSM come with cruise? If so, see how that's set up.

It did not. Those of us that added it did so after one of the many one-way valves Mazda installed.

Bingo.

More info?

I was approaching it as the car was accelerating past the cruise set point so the car was backing off the slow it down then when it when to readded power it would boost again and get stick in s a cyclical for gas on and off. No that the boost was kicking the CC ass.

The speed has a bunch of green & white valves on various vacuum lines so that sensors (and brake boosters) that expect to only see vacuum don't see boost. Before my Audioshit crapped itself, it was connected behind one of the check valves so it only saw vacuum. I have no idea what would happen to a vacuum actuated thingamjob when it saw boost, wouldn't be surprised if it acted like your symptoms though.

Did it work before and suddenly not? New install?

https://www.miataturbo.net/attachmen...ine=1320179748

Will try this and see if it works after ecu in in and working.

Didn't do it tell I installed a relocated TB and bov on my hot side mp62 so that it runs like a turbo. No more TB preblower.

My old turbo car had an identical problem that I never sorted through. I did try
- Check valve.
- New air line.
- Relocating the air line to different places on the manifold and tb.

I figured the check valve would have at least changed the symptoms, but it had no effect. I only spent about 20 minutes on it before giving up. Ended up replacing cruise control with a trailer and turbo diesel with cruise control.

My car likes to go from 8vac to 5psi in a blink of an eye as the bov closes and the air has no where go. That's why the car accelerating then decelerating making it start a endless loop of trying to get back the the speed I set it to.

If i am not in CC and try to go up a hill my self the car tends to try to run 3-5psi up the hill and accelerate. I have to modulate to keep it around in vac or around 100kpa

Interesting, I have OE cc and no problems using it. It's fun to hear it pickup on hills and let off with a wooshshshsh when I get to the top...on its own. IIRC the signal line is one of the small fittings just behind the TB and it has no check-valve on the line.

Not much help other than mine worked fine on my 99 after I DIY turbo'ed it. I used one of the little ports on the IM as a dedicated line to the CC and no check valve.

Mine does the same thing. The problem as far as i've found is the turbo miata speeds up too fast for the cc to react so it quickly goes above the set speed at which point the cc eases on the gas too much and then it falls bellow the speed limit, the cc pulls its standard amount of gas which again is too much and speeds up too fast making it a cycle until you help it set its speed.

Problem is 10% on the tps without turbo gets you to 50-60kpa. 10% on a turbo gets you in boost.

My cc works like it stock when i unhook the wastegate.

Ya was thinking maybe i to much ftlb for CC to handle

That is another reason why i was looking for a variable throttle wheel.