Fd sticking high idle
 

My fd has a sticking high idle around 1250. What's strange about it is that you can pull it down to normal idle speed by loading the car down a bit with letting the clutch out in gear and then allowing it to idle again and it will be perfectly in spec then. I've tried several different tps and throttle body settings. Running a stock Ecu that I have also swapped with a known good with the same results. Fast idle cam, dashpot, and throttle cable is all set correctly. All new gaskets and hoses down to the lower intake as well. Problem was there prior to lower intake gasket job as well. I've tested the idle control valve. And the car also has a brand new engine wiring harness. Everything functions perfect when driving except the sticking idle, perfect sequential boost pattern. Brake, clutch, and neutral switches all function good and are in adjustment. The only thing I've noticed is the car is experiencing intermittent speedo issues where the speedo will sometimes bounce with the tach at idle. Possibility the Ecu is reading speed and causing the engine to not return to idle speed? Any other suggestions?

how do you know the clutch switch is working? Do you have a check engine light? How about vacuum leak?

The only way the car has a high idle is if air is getting by the throttle body. Period.

See if you can manually force the TB closed and if that drops the idle. If you pull the throttle body elbow off you can see into the throttle body. There's a hole down at the bottom in front of the primary throttle plate, that goes to the ISC. You can plug that up with your thumb, if the idle drops/car stalls then it's something with the ISC. If that doesn't change things, it's either a vacuum leak or the throttle plates themselves aren't fully closing.

Thermowax sticking could also be an issue, that will prop the throttle plates open as the car warms up. Stock, the car revs to 3000 RPM on startup (AWS), then settles to around 1200-1500 RPM. That should slowly come down as the car warms up and the thermo wax rod extends.

Dale

No check engine light, I don't think it's a vacuum leak as otherwise it would be there all the time, and like I said I'm able to put just a small load on the engine... even just turning the steering wheel is enough load most of the time to make the car return to its normal idle speed, and once it does it will stay there with or without load and idle perfectly normal. Tested the clutch switch with my fluke meter and all appears to be good, plus the interlock functions as it should when starting the car

I think Dale might be onto something with a possible isc issue. I'll pull the elbow off next chance I get and see what that tells me

Hey - I know this post is like a year old. But I just acquired a completely stock 1995 RX7. It is doing exactly what you say in this post. Starts at 3000 rpm, comes down to about 1500 but doesn’t decrease once warmed up. This is our first foray into dealing with a rotary motor. Can you please share how to check or adjust the therm wax rod for proper operation? Thanks so much!!!

Since the car is stock, you should get the factory service manual and look up the fast idle system in the Fuel & Emissions section. A lot of the idle advice you will get is for making adjustments on an aftermarket ECU, most commonly a Power FC. You don't want to go that route.

The fast idle system is similar to what was employed on piston engines at that time, it's not rotary specific. It's like something you would find on an old carb or something. It forces open the throttle, and then as the coolant warms up expands a hot wax rod to close the throttle and bring the idle down. You should be able to reach behind the throttlebody and rotate the fast idle cam down with your hand (use a glove, it's hot back down there) and it will drop the idle, if it had been sticking.

Thanks much!!! Makes sense and we’ll def try it this evening. Just downloaded the manual.

Have you checked to verify that the butterfly spring on the TB itself isn't sticky? I had something similar happen years ago and a bit of carb cleaner where the throttle cable connected in sorted it right out!

Yep, fast idle cam on the back side of the throttle body. It's probably just stuck.

There's a thermowax that has coolant going through it, as the motor warms up the rod extends and kicks down a cam that keeps the TB open slightly. Normally the car is 1500 RPM cold then comes down to 750 when fully warmed up.

Also, if there is air in the system and the coolant isn't topped off that could cause the high idle. Or, if you just haven't let it warm up, it's normal.

Dale

I encountered a similar sticky fast idle problem when my car was around 5yrs old. It turned out to be clogged coolant passages in the throttle body near the wax pellet actuator for the fast idle cam. Cleaned out the debris and idle returned to normal with no further problems.

So we tried adjusting the fast idle cam and it didn’t make a difference. We need to replace both belts so we decided to check butterfly springs at the same time. Car has been sitting for a couple years; so they could definitively be sticky. Sure appreciate all your suggestions!!

How did you do this? Thanks!!

All - first off, thanks for all the positive advice. We did clean the throttle cable with some carb cleaner. It was filthy and sticky. Couldn’t hurt anything to clean that up. Then we went back to the fuel & emission chapter of the manual. Using a flashlight and mirror we were finally able to locate the air adjustment screw. The hubby was able to get a screwdriver on it, without removing the intake air elbow, while I sat in the driver seat. He turned it all the way closed and then opened it a quarter turn. Not much of a difference, so he turned it another quarter turn. WOW! The engine immediately started hunting. He turned it a bit more and the engine began to settle in. We got it to lower from 1500 RPM to about 1000 RPM once the engine was warmed up.

At that point he moved on to the throttle adjustment screw. With that we were able to stabilize RPM at about 800 RPM on the fully warmed engine. We’ve checked it for the last 2 days and all seems to be well. We start at about 3000 RPM, settles in around1200 RPM, then relaxes into about 800 RPM once all warmed up.

Thinking this works well for a 100% stock setup. Thanks again to everyone for their help! You’re all awesome!!