yes that should be the screw, it rests on the t-wax plunger so thats it.

As far as how to reach it I don't know you might have to move something out of your way...I've never had to touch this screw on my NA thankfully.

 

Hey guys, I have been doing some thinking about the hunting/ bouncing idle thing, and trying to come to more of a bottom-line "root cause". I read a different thread the other day with the same topic and one poster (might have been Hailers, I can't recall) had said that around 1100 rpm is where the stock ecu timing advance map kicks in. I would imagine that the ecu uses not only rpm input but also tps input to determine the spark advance point. The idea was that if the rpm is held (by whatever means) at about that 1100 rpm point, the ecu is ready to start advancing timing, but my thoughts are if the tps reading doesn't coincide with what is programmed into the chip of the ecu at that rpm point, then there would be a cyclic "advance, no advance" condition back and forth. Make sense?

This could be verified easily with a timing light and voltmeter (or better still a lab scope, I use one daily for tps checking where I work). My TII isn't running yet, but I have a TII at work right now that I'm doing brake work and idle diagnostics on for a customer,I'll see if I can duplicate a hunting idle around 1100 rpm and see what I can come up with.
It's becoming more apparent that the first steps to take in diagnosing this type of bouncing idle is to make sure the idle lever is firmly against the stop screw (the one with the locknut) and if it's not, fix that first, whether it be t-wax, dashpot, tight throttle cable, etc. and then do vacuum leak checks, then tps setting, then spark timing. I'd like to get to the root cause before making adjustment screw changes if at all possible, so I'll experiment with this and get back to you guys.

I bet that if I had asked Greenbudd to watch his timing marks in my first post, and if there were significant change in timing that corresponded with the hunting idle, we could have nailed his problem much sooner without umpteen pages of "try this, try that". On the other hand, without the effort, we wouldn't have learned as much, kapish?

 

nm

 

Well, I just got a new timing gun a couple weeks ago, but never actually checked the timing yet. It would have been neat to see whether or not the Timing was actually being advanced intermittently.

Though, like scrip said, the timing wasn't necessarily bad, just that the idle was, for one reason or another, being held at that awkward stage where it causes the ecu to advance timing back and forth, actually causing the bouncing idle.

The initial high idle could be due to a number of things but in this case it turns the t-wax was keeping throttle plates open a bit too much during startup and warm up, so we adjusted the fast idle clearance with the Fast Idle Cam Adjust screw and then readjusted the tps and bac to even things out again.

But I'm wondering how my Fast Idle Clearance could have slipped into that funny spot, as stated earlier in this thread this TII didn't always surge but it did always have a weird high idle, not this cyclic surging, what could have made it start doing this, just a bump in the road or just getting jostled during some driving IDK.

Then my t-wax was also not receiving it's fair share of hot coolant due to kinking coolant hose under UIM. There were also lots of vac leaks and miscellaneous little things.

 

So I went ahead and prepped the motor for some paint, I just want to do the housings I think, the irons are still perfect and will look great with some clean up.

Cleaned Up Engine:



Some Paint:




I still need to paint the front cover, I think I'll do the water pump and neck black, but look at this.

I noticed an odd hole and what looks like a crack in the aluminum front cover on the front lower right corner:

 

What do you think about the crack that little hole on the front cover? The hole just happened when i was cleaning the block and the crack I imagine has been there for a long time, is that a high stress area of the motor, what would happen if it cracked more right there? Should I consider getting a new front cover?

 

Well you're in luck Greenbudd. I have an s4 timing cover in front of me. The hole is actually a perforation from the original drilling/ tapping of one of the oil pan bolt holes. It isn't exposed to oil from the inside, so there shouldn't be a leak. As for the crack, believe it or not, mine has the same thing. It's not a crack at all, just a casting mark. Mine is in the exact same location and is precisely the same shape. So no worries.

Kinda strange, but if you touch the casting you'll notice it's smoother on the left side of the casting flash (crack) than it is on the right. Just an observation.

 

excellant news, thanks for the information.

 

Here's mine. Ironic isn't it? As you can see from behind the cover, there's no leak path.

 

Yeah thats crazy, I was just going over the whole block and I was like "Oh No!!" so it's a great relief to find out it's just casting marks, those were the only things that caught my eye.

I was actually surprised at how easy the block cleaned up, some carb cleaner, some compressed air, a lot of scraping and wiping, a couple hours later and she was ready for paint, I primered with Metal Ready then rinsed with water and let dry before the Por15 Engine Enamel.

Like I said the front cover will be done, I wanna look at how some of the others did it, I'm thinking the water pump and neck black but the rest still orange (Hemi Orange at that...)...IDK we'll see.

 

Looks great for sure!....hey this is off-topic, but I noticed it says you're from Green Twp, New Jersey......is the "twp' a typo or am I just not good at geographical abbreviations?

 

haha...I always thought Twp was the abbreviation for Township.....maybe not.

I live in a small town called Green in Northwestern NJ. Its funny cause I travel across the width of the state everyday to get to work and back, I work right outside of New York City but get to live in my rural town still so it's nice.

 

I would have never guessed "township". I guess I learned something new today. Man that's quite a commute for ya! I guess you drive your Volvo to work or the GXL?

Ok. I duplicated the hunting idle on a '88 TII that I have at work. I manually held the throttle at 1100-1200 rpm and watched the timing. It advanced 6 degrees from base timing and back and forth until I released the throttle. So basically, anything holding the idle that high will cause the bouncing, whether it be thermowax, vacuum leak, tight cable, dashpot, BAC screw, or whatever. It doesn't have to be strictly a bad tps as so many on here have suggested.

Bottom line is: The idle speed must be kept at or under 1000 rpm with the tps set correctly to prevent the bouncy idle. So, in my opinion, when other people have a bouncy idle complaint, the diagnostics should start with:

(1) A visual inspection of the throttle lever to insure that it contacts the stop screw (by using a mirror and flashlight or temporary removal of the intercooler)

(2) If a gap is found between the throttle lever and stop screw, inspect thermowax and fast idle cam position adjustment, dashpot function and adjustment, and throttle cable slack.

(3) With the throttle lever against the stop screw, perform vacuum leak test using the propane method or compressed air method and make associated repairs.

(4) Set timing to spec with engine below 1000 rpm.

(5) Adjust A/F mixture screw (if equipped) to obtain smoothest idle

(6) Adjust BAC screw (if equipped) to obtain 750 rpm idle (or your preferred speed at 1000 rpm or less) and re-adjust A/F mixture screw if required.

(7) Adjust TPS per FSM and re-adjust idle speed if necessary.

 

i like that. we need more layouts like that for idle problems. step1, step2, etc.

thanks guys.

 

Awesome layout. Thanks for the step-by-step, and thanks to GreenBudd and (who I now refer to as) the Big H .

 

Good work scrip. Just to clarify though, all of the above should be done with a fully warmed up engine right?
On a cold engine the fast idle cam should be holding the throttle plates open a little, wouldn't that be represented by a small gap between the throttle lever and the stop screw?

I'm waiting on my butt load of parts to arrive, so I figure I'll clean and paint the engine bay this weekend and then start the re installation shortly there after.

I'm really thinking about moving my build to a new thread so we can let this stay as it is for the idle troubleshooting. What do you guys think?

 

You are correct-a-mundo my good friend. Cold fast idle, warm idle @ 750 or your preference. I probably should have added that the procedure applies to cars with stock ECUs and engines with stock porting or mild streetporting. Cars with standalones probably wouldn't have a spark advance map with such an on-off advance rate @1100 rpm like the stock ECU. And guys with large streetport or bridgeported engines might want a higher idle speed, making it necessary to use the "forbidden" base idle screw (with the locknut).

 

I wonder if the rtek 2.0 retains this timing advance map, i guess so from the symptoms of the car it does indeed retain this feature, though even if it does i'm wondering if we can get rid of it with the timing map adjustments, maybe I'll run that by an rtek guy??

 

Sounds like the thing to do. I wish I could help in that area, I have zero rtek experience. I know with a Megasquirt you can tailor the fuel and spark maps to your needs pretty easily. I play around with that software on my pc occasionally and will be doing the same on my laptop once I get the car together and running.

 

a small update:

I have decided to not post in this thread any longer unless it is specifically idle related. I will inform you when I start the other thread on the build by dropping a line here, I just don't want to lose the focus on the good progress we have made here.

So when I make some new progress with the build I'll let you know, on a side note I just bought my first Mig welder from Lincoln (love my new job) and am looking forward to learning how to weld now.....but we'll see more of that in the other thread I will start.

For now I think we have pretty much nailed this cyclic bouncing idle.

 

Sounds good. Any way you can update your main page's 1st post with the guidline that scrip7 posted? Would make it easier on new readers looking for a quick guide.

 

It would take a Moderator to do that. I have written several informative posts and threads with requests for Mods to archive them, sent PMs, etc with no response. I was also given a chance to write articles on another site, but another expert-wannabe beat me to that. All is well.

 

I think it's worth it to read the thread in it's entirety, it's good to understand the process that leads to your results. I learned a great deal about my car by going through this 10 page ordeal and I think that maybe it's better off left to those who take the time to read and want to learn how their car operates and how to maintain it.

I just watched all the videos again , and was blown away by how "noobish" i sounded about the whole idle concept. It's unfortunate that sometimes it takes something to break or malfunction to initiate any kind of curiosity as to how these cars work. I love my rx7s and view their ownership as an experiment in learning.

I'm surprised at times, how easy it is to be misinformed, or uninformed, about something that is essential to our cars operation. I guess we just take it for granite, while it's working, that it all just does something. Hailers said something like, people get scared and remove things because they don't know what they do. I can't agree more on this. Just because one doesn't know how something works doesn't make it some magical mysterious problem. Ignorance is forgivable until you ignore offers of help. Here is a great chance to get some solid help on idle conditions.

 

Well spoken Greenbudd. Hailers made a great statement about removing things unnecessarily. So many people remove their thermowax and BAC just to tidy up their engine, and a few others claim they do it for weight savings. Someone makes a thread about doing these mods and suddenly everyone thinks they should rush right out and get it done 'cause they think it's "cool". I prefer to have a stable idle at all temps.

 

Here is the continuing thread.
https://www.rx7club.com/showthread.p...19#post7165419