First post in this forum...hehe...

My 1991 has a high and erratic idle-- generally when I start it up, it'll warm up at 3000 rpms, drop to 2000, and eventually coast down to around 1000, but after it's sitting out in the sun it doesn't warm up and goes straight to a 750 rpm idle. Is this usual?

If not, does anyone else experience this, and have any knowledge on what's exactly the problem, or will I have to go through the full list of idle fixes?

Thanks in advance.

 

That sounds normal if you start the car in neutral. It's the accelerated warm up process. Try starting the car in gear and I bet you it won't do that.

 

its normal. theres a sensor on th radiator that switch's on depending on the temp.. from what hear

 

The fast idle shuts off (goes to 750 due to the thermowax expanding) around 150F. If your under hood temperatures were that high (or near) then it would make sense for the fast idle to not kick in (theoretically).

But... are you saying normally you don't get a 750rpm idle at all or that it will coast down to around 1000rpm then finally settle at 750rpm?

My car only idles perfectly while it's warming up. Not quite to normal operating temperature, but close. After that my idle goes to **** (yeah yeah... I'm working on it ). On the warm start does it go straight to 750rpm then go to crap afterwards?

 

All right, that sounds good. (Black car, 90+ degree weather under sun)

And I normally get a high idle (around 1000), but on the warm start I get the 750, so I guess I still have some work to do.

 

Updates!

Warm start: Idle goes straight to ~750. I can't warm start it at the moment because it's not hot enough.

Start in neutral: Car warms up at 3000, then drops down eventually. Idle is 2000.

Start in gear: Car goes immediately to idle, which is about 1750, noticeably different from the idle when started from neutral.

 

Sounds good to me.

 

Okay, so my problem is just a high idle, right?

 

After the car is fully warmed up, you will have a 750 RPM idle. Is this what happens? If so, then everything is working as it should.

 

You can unplug the AWS which causes the engine to shoot up to 3000rpm. Which you don't really want to have happen. The AWS is on the drivers side of the engine and is connected to the Dynamic chamber. Well, I suppose a picture or just the FSM will help you out more on this then I could explaining it.

Without the AWS, your engine should still always shoot up to about 2000-2300rpm due to the BACV, then it should idle down and the thermowax will take over.

 

Mazda issued a service bulletin saying the AWS was broken on these cars..
If you take the AWS out and leave the BAC in, the car will NOT idle high. You should look for the TB mod thread (in the archives or maybe at RETed's site fc3spro.com) and do that - solves a few idle related problems including this.

 

That's news to me. TSB number?

 

i have seen a tsp about the AWS but i think it was a description of operation. to let technicians know that at colder start ups the engine will rev to 3000