Idle dip when putting into gear
 

So I just replaced my motor on my FD with a crate Mazda engine, and noted the car has an idle drop when I put it into gear. The RPMs drop 500 (to 250) from 750 where it was at then it blips and eventually settles back around 500. I have seached and i found several post with the same issues, but no one referencing the fix. Before I go dicking with the idle screws, what am I missing, or why is it doing this?

Unfortunately the clutch has nothing to do with it, it is only putting it into gear. I will look into the neutral switch on the transmission and just see what it does with it unplugged. It seems like that's most likely part of the culprit

What are some very specific set of sequence that has to happen. It must be under a warm up cycle of some variety, the air conditioning must be on, and it must be in gear and that is the only circumstance that will cause the issue

AWS is part of the Idle Speed Control System, page F-81 in the FSM. I think that's where I'd start to sort out your issue. Not a lot of help, but a free bump for maybe getting something more specific.

Do the idle speed tuning procedure in the service manual. You have to jumper TEN and GND and then adjust the air adjusting screw.

My car is a JDM, I don't know if I actually have the AWS. Wasn't going to manual it does not look like something that I worked on or around.

I unplug the neutral switch and it still stalls under warm up sequence and idle hunt a little bit as well. I did the brake cleaner test and could not find any vacuum leaks but I do not have a smoke tester so it's not entirely definitive.

I will look into resetting the idle does anyone have copy of it?

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I followed the procedure exactly as laid out, and I still have a weird idle surging and hunting.

Also when you first start it up it's decided to go completely wonky and surges and does all sorts of weird stuff.

here's a video of what it tries to do when you cycle the air conditioning on and off.

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Another very relevant detail that I just noticed. I finally tried to spool the turbos now the motor at least has a few miles on it and I pretty much only get one spool and then it just sounds like it's running on A massive vacuum leak. I built a leak tester so I will smoke test it tomorrow. But they're still nothing visible

I would say to check for air leaks, and clean the idle speed control solenoid.

I have done both, and confirmed vac leaks and still have the dip.

is the TPS in spec? Are there any error codes?

You do have the stock ECU right?

If you have an aftermarket ECU it's a different situation. If you have the stock ECU, you're just going to have to go through the service manual troubleshooting guide section by section for your symptoms. Since you are JDM you won't have accelerated warmup system, front catalyst, and I think EGR, and some parts are going to be in a different location.

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Now that I'm fully driving, it's far expanded from the original post, so more an update.

So fresh start the car does not high idle, instead it revs to 2500 rpm and then immediately drops to normal idle.

Put the car in gear with the air conditioning on and it immediately nearly stalls. Every time you come to a complete stop with it in gear it will stall or nearly. After about 10 minutes of driving it will no longer stall and run and drive kostlm fine, with only one issue... Throttle tip-in and when you let off are overly aggressive. it feels like you're driving a car without a throttle position sensor.

As you roll into primary turbo at stumbles about 3 times and it's completely fine into secondary. If you let the RPM wind down from Red Line it starts misfiring and idle hunting for about 15 seconds and then it will idle and drive completely fine again.

​​​​​​All all my experience and everything makes it seem like it's the TPMS or vac leak, but it test within spec within the narrow and wide band, and doesn't fail a smoke test even with 20psi. All vacuum lines have been checked, idle has been reset, TPMS has been readjusted, idle control valve has been cleaned and tested. I'm at a loss of what simple things I have got to be missing. It did none of this shenanigan before I replaced the motor.

Did you ever check for error codes?

Yes, no error codes either. Just a steady light from the LED

What ECU are you running?

The car is a 99% stock 92 JDM FD with 44,000 miles. It's completely original, and extremely well kept. The only modification is a Jasma catback.

Tomorrow I am probably going to review all of the switches on the transmission and make sure they're all adequatly connected, hooked up correctly, and are reading what they should.

It seems the idle dip is not associated with the air conditioning as much as the air conditioning exacerbates the idle dip. I'm wondering how gear selection switch interacts with the ECU. It appears that goes into a completely different running map. Perhaps the switches on the transmission are crossed or not reading correctly causing that map to have a different reference point?

Did you get this sorted yet? All of a sudden my 92 Type R started to stumble and misfire, feels like 1 rotor, when put into any gear. It's almost intermittent at times and getting difficult to troubleshoot. Only when it clicks into gear.

My issue was resolved by installing a power FC. I could never find an issue with the car. Most common scenario is likely a vacuum leak. I definitely recommend getting a smoke test done or building your own at home.

@Sgtblue I need to give credit where credit is due even if it is 18 months later.... This man was spot on I finally tore apart the clutch switch and found the spring shattered to pieces. I had eventually got in the car to run without issue using a power FC ECU, and just barely bumping the idle up. But I could never get out of the back of my head that that was not the right solution. Having forgotten entirely about this post I dug back into it and tore apart the switch for the recommendation from someone else on another thread.

I finally returned to this thread to give closure to it for search purpose and see the first response but I had dismissed because of being so caught up in my own world was the solution I needed...

@Sgtblue you rock, you should have listened to you years ago!

👍

Yep, I started looking at this thread and immediately thought "clutch switch". Glad you found it!

Dale