Having a strange idling issue with my imported FD, car came from japan. Basically when i would take the car out during the day i noticed when idling the RPMs would fluctuate between 900 to around 400 sometimes lower (it will bounce up and down this range until i start driving again). At idle, if i rev it a little, as soon as i let off the throttle it will almost stall (sometimes it will stall) dropping down to below 100 RPMs it seems before raising back up and continue bouncing between 400 and 900. This idling issue is fixed by simply turning on the headlights ONLY. With only the headlights on the car idles perfectly around 850 RPM. Then one day when driving in the rain i had my headlights on, A/C fans (no cold air in the car so A/C wasn't turned on just fans for air flow), and wipers on. With all these turned on the car would die when put into neutral, even if cruising at speed. The car always fires right back up no problem every time after stalling but the idling issue continues unless i have ONLY the headlights turned on.

Things to note: battery is new, alternator was checked yesterday and is performing as it should. Something is draining battery from the car while it's off and i haven't figured out what yet so i have to unplug the battery every time the car goes back in the garage. Aftermarket electronics (installed in japan) include: hks turbo timer, some type of alarm system, head unit, and some unit that is responsible for giving the "sleepy eyes" look mounted on the steering column. All of which have been turned off except for the alarm which has no off switch or any button for that matter.

The car dies ~5 seconds after starting 40% of the time but never fails to start back up immediately never stalling after the second start. If the car is revved up in neutral the RPMs will always fall to around 400/500 (sometimes lower) then rise up to 850 and hover there.

I'm thinking it's a bad ground somewhere. What do you guys think the problem here is? Is there someone that's had a similar experience, if so were you able to resolve the issue? I live in central Florida. Any help is appreciated, thanks all.

- Daniel

 

Hi Daniel -

Hands down first thing to do is clean the ISC (Idle Speed Control). They get gummed up over time and can't react properly to provide idle air. When your foot is off the gas, the throttle plates are closed, and the ISC routes a measured amount of air around the throttle plates to set the idle speed. When you turn on the headlights or turn on the AC, the ISC opens up further to compensate for the load on the engine.

The ISC is on the back side of the upper intake manifold, it's visible just by looking and you don't have to pull the UIM to get to it. It's held to the UIM with 2 10mm nuts and there's a white 2-wire plug going to it.

Remove the ISC from the car and get some carb cleaner. Spray the inside of the ISC with carb cleaner to get all the carbon and gunk out of it. You may want to use your fingers to slightly pull the white piston inside down so you can get carb cleaner in between it and the seat it sits on (the air passage).

Bolt it back up and see how she does.

I would also put in a fresh set of spark plugs if you haven't done so, that will fix all kind of weiird issues. It's frequently neglected and new plugs are a world of difference.

Dale

 

Thanks for the response Dale. I removed and cleaned out the ISC with carb cleaner, there was noticeable junk built up inside and it cleaned up nicely. After reinstalling i went for a drive and unfortunately this did not fix my idling issue. It seemed to perform slightly better during start up but once the car was warm the idle went right back to bouncing up and down when at stop lights with no additional electrical load.

I tested to see if having only the AC fans turned on would have the same effect as the headlights for keeping a steady idle, and it worked. So basically whenever i approach a stop light i either turn my lights on or the AC fans on to keep the idle steady, then once i start driving again i turn whatever i turned on, off. Based on how the car reacts to additional electrical load (remember it would stall when put in neutral with AC fans, headlights, and windshield washers all turned on) do you think my problem is still related to the spark plugs? Spark plugs are hard to check for me right now because i do not have access to proper jack stands but will have access in the coming week, any other suggestions in the mean time?

 

Spark plugs are easily done from the top of the engine. Remove the throttle body elbow (4 10mm nuts and 1 hose clamp) and you can easily get to them. Some people like to do them from under the car, but in the time they take to get the car on jack stands I'm halfway done changing plugs. Just make sure not to mix up plug wires and give the plug wires a once-over to make sure they look OK.

Next thing is the clutch switch. with the stock ECU if the clutch switch is bad you can get a bouncing idle. Good thing is you can actually fix it with the spring from a ball point pen. I did this myself probably 10-12 years ago and have had zero problems ever since.

https://www.rx7club.com/3rd-gen-arch...switch-495391/

There's other threads out there about the clutch switch as well, some have pictures. Also there are 2 clutch switches, one is for the starter and one is for the ECU and cruise control. The second one is the one to fix.

Dale

 

“Things to note: battery is new, alternator was checked yesterday and is performing as it should. Something is draining battery from the car while it's off and i haven't figured out what yet so i have to unplug the battery every time the car goes back in the garage.”



If you’re disconnecting the battery every time you park the car, you’ll need to do the idle relearn procedure. Failure to do that will cause issues like you’re describing. You didn’t mention whether you were using the stock ECU or not but I may have missed it. Here’s a link to banzai for the factory books Foxed.ca - Mazda RX-7 Manuals. I would read up on how to set the settings correctly before you start trying to troubleshoot. Vacuum leaks, improper throttle body settings, tps adjustment are all things to check.


~ GW

 

^Yep, good points there.

I forgot to address that part of your first post. The headlight controllers and alarm system is probably the #1 culprits for a draining battery. May figure out how to at least disable them to see if that's the problem.

Even with a disconnected battery, though, I don't think you should have THAT much problem with idle. I'm really leaning towards clutch switch.

Dale

 

I will check out the clutch switch later today after work and read up on the idle relearn procedure; i'll report back with what i find. Thank you two for the suggestions!

 

I was able to have a roommate check out the clutch switch for me, what they told me "the white cylinder slides out of the switch smoothly when pressure is applied to the clutch. If the clutch is pressed down all the way there is about a 2mm gap between pedal and white cylinder."

The car did not have this idling problem when i went to see it for the first time and i don't remember having this issue the first week or so of ownership (after about the first week i noticed the battery was being drained so i started unplugging it) so maybe it is the idle relearn procedure...i'll read up on that and report back later

 

Also car is running the stock ECU, does idle relearn procedure apply if I do not have a PFC?

 

That's a tough one man. There's some very knowledgeable rotary guys out in your neck of the woods (Tampa, especially). I'd probably reach out to them and see if they can give the car a look over and confirm that everything is working properly. I'd also consider changing out that ISC because it sounds like it could possibly be bad.

 

Since posting the car had developed an issue and wouldn't accelerate past 100kmh so i decided to drop it off with someone i trust to work on the car. No error codes were found when the scanner was plugged in but all codes were reset anyways and the car drove like normal again. I was told the ECU wasn't communicating with the scanner or check engine light and that my issue should have prompted the check engine light to turn on. So as of today the mechanic is sorting out the car electrically and doing what he can to get the ECU to start communicating properly again.

I spoke to him about the idling issue and when he tested it out for himself he brought up something I forgot to mention. The car idles fine during warm up procedure, hangs around 1700-1500, drops down to 1000 after a few minutes, then again drops down to around 850 RPM. There is no bouncing in the idle until it hits the normal idle, i'll post back in here the solution if he manages to sort it all out.

 

Ohhh boy. Alright, so the new "issue" that you're having is not an issue, it's present on all stock Japanese cars. They're all limited to a top speed threshold...hence why the first thing most RHD guys do is aftermarket ECU. With that being said, I know you trust this mechanic. Most people have a mechanic they trust and wouldn't let anyone else touch their cars, but I'm going to assume this is your first rotary powered car. First and foremost he should've told you out of the gate that all Japanese cars with stock ECU's have a limited top speed, if he's ever worked on/ been around Japanese import (which are VERY common in Florida). However, you SHOULD NOT have just anyone working on your rotary powered car. They're not terribly different than piston driven cars as far as theory of operation, but different enough that they usually will not have much, if any luck rectifying your problem. If this gentleman has prior experience working on rotary powered cars, then thats cool. If not, I'd suggest going to get your car immediately and taking it to one of the many reputable rotary shops in Florida.

 

He said 100kmh though, the factory speed limiter is 180kmh.

That aside, the early JDM FD's (if not all), don't have a check engine light. Maybe he is simplifying things for you but yea I wouldn't feel comfortable taking my car to someone that isn't very familiar with the FD, atleast, and better yet with JDM ones.

 

Its been 8 years since I left Japan so I couldn't remember exactly what it was, thanks for reminding me. This is beginning to sound like an ECU issue. Then again, without seeing the car in person, I wouldn't know for certain. I'm just throwing poop at a wall...and trying to push him to seek proper help and get this car fixed by someone who knows their way around the chassis.

 

He’s an experienced rotary mechanic, not just any mechanic. But you’re right, this is my first rotary and my first import so everything about the car is new to me. The error codes were reset even though one wasn’t showing up, after the reset the car was then able to go above 100kmh. When the car would randomly stall on me (read previous posts) the heat light would turn on for the catalytic converter and what I thought was the check engine light would turn on but would go away as soon as I started it again. The car is a headache electronically

 

Man I wish I could put hands on this car, mostly because I'm curious to see what the issue(s) are. Good luck to you. Keep us updated!

 

I picked up the car last night and it's running great. The vacuum hose associated with the blow off valve was replaced and a new cap was installed where a boost gauge hose would go. The throttle control valve was also adjusted through trial and error to see what made the engine happy. I was told the air pump was involved in the issue but was never messed with or adjusted, just that it had a role in the problem. Those seemed to be the main contributors for the idling problem i was experiencing based on what i was told. So the idling issue is resolved, and it was not related to the cars electrical issues. Cleaning out the ISC (I did this before taking the car to my mechanic) helped a little as well i believe because there was noticeable junk built up inside. The 100kmh issue was solved by resetting all error codes through a scanner even though none were popping up.

I had test drove two other RHD RX-7s before purchasing this one, the one i decided on was in the best shape mechanically and cosmetically. I never noticed a boosting issue with the car. It's very obvious to me now that it was having boosting problems before. It drives much smoother now and feels like it has more power in the lower to mid RPM range.

The upper intake manifold was removed so the vacuum hoses under it could be inspected. I was told they were all good: looked pretty new and were connected correctly. Spark plugs and wires were checked, they also are pretty new and did not require replacing. To sum it up, the car runs smoother and feels like it has more low end power after getting it back from the shop. The exhaust sounds slightly more quiet now with a lot less "pops" or backfires too.

 

Nice. Yeah, if the air pump isn't running with a stock ECU (due to a faulty connection or blown fuse) the idle will be rough and on/off throttle will be rough.

You making good boost to redline?

Dale

 

I do not have a boost gauge connected yet but based on feel, yes