I’m having trouble fixing an idle issue with my car. I’ve just recently rebuilt and changed almost everything on the car. The problem I am describing began before this project started, and continued with the new components (as they always seem to do). On first start up I noticed a massive fuel leak shortly after the car warmed up. The fuel leak is now fixed and I'm going to try to trouble shoot the idle issue more, and maybe get a first ride this weekend.

When I first got the car the only mod was a DP and horrible cat-back with a 5" tip tortoise launcher exhaust. AWS, Double Throttle, and ISC were in place. There was no clutch switch installed on the car at the time (didn’t know this until later). ECU was stock.

Below is a description of the problem:

- Engine starts up and bounces from 1200-2200 rpm constantly.
- Once the fast idle cam opens it holds steady at 2200 rpm with the clutch in, and trans on neutral. Idle is slightly lower in gear with the clutch in.
- There was a dead spot in the throttle cable at low rpm when starting from a stop. I thought this was a sticking throttle cable and replaced it, now I think it’s due to the high idle.

The engine has been rebuilt. Clutch switch installed, AWS and Double Throttle removed, ISC in place.

These are the steps I have taken so far.

- Adjust TPS per FSM using the voltage output screen on the PFC commander. (Done at first cold to get close, redone hot as specified in FSM).
- Set air bleed screw per PFC learning procedure (1/4 from full shut)
- Adjusted lock-nutted screw on the front of the TB so its not holding the throttle open at all.
- Adjusted new throttle cable per FSM.
- Tested the system with the ISC hooked up with the same results as above (did not reset PFC to re-learn).
- Removed ISC and tested per FSM (reads 12.4 Ohms which is over the high limit of 12.3). Installed a block off plate in its place. Engine idles at 1200 rpm solid, just needs a blip of the throttle at start as it stumbles a bit at first. No data after warm up due to the massive fuel leak .
- Re-installed ISC. Tested value is close to the limit and I'd rather have it there if it’s not the cause.

Before the rebuild I did the cheap bastard intake box mod, after that is the first time I remember having this problem (car was fine when I first got it, for about 300 miles). I've been thinking the problem is a lean condition. My wideband reads 16 - 15.6 AFR at idle with the air pump hooked up. I have yet to add fuel to get to the ~13.5 AFR number I've been told is more appropriate.

This weekend I plan on pressure testing the entire system as a sanity check. Since everything is new I am positive there are no vacuum leaks, but you never know. If there are no leaks I’m going to try tweaking the map until I get something close to 13.5 AFR. If that doesn't work then I'm lost.

Am I on the right track? Since it seems like the added air of the intake mod could have started this, I'm hoping more fuel can fix it.

Relevant mods are as follows:

-PFC (newest version base map)
-Aeromotive FPR (set to 44psi with boost ref @ 0psi)
-Denso supra pump (rx7.com version)
-Braided fuel line (-6 AN)
-FPD eliminated
-FPR hooked directly to vac source on LIM
-550 primary, 1300 sec
-HKS RS intake
-Pettit Coolcharge III intercooler
-Greddy Elbow
-IRP Stage 2 Street Port and BNR Stage 3's
-HKS Twin Power
-9’s all around
-DP, RX7.com mid pipe w/ High flow cat, RB catback

Thanks for any help.

 

If you have a high idle, there's only one way it can happen - air getting around the throttle plates into the motor.

This can either be -

- Stuck or bad ISC. Pull the ISC and clean it with carb or brake cleaner, lube it with WD-40, hook 2 jumper wires up to the 2 terminals of the ISC and hook those wires to positive/negative on the battery and "click" the ISC open/closed a few times. I have seen ISC's with junk stuck in them that makes them stick open.

- Vacuum leak. Any air that gets into the engine past the throttle body will raise the idle. You can test for this with a can of starting fluid - spray in short bursts all around the intake tract. If it sucks the fluid in, the engine will rev up a bit, it's obvious.

Other things to check are the vacuum lines to the brake booster, making sure the upper intake manifold is flat and square on the lower intake manifold flange, making sure you have the rubber grommets at the base of each injector that seal it to the manifold. Also, the PCV valve to the oil fill neck could, in theory, be bad or installed backwards. This can be totally eliminated, cap the neck and the nipple on the manifold, it's not needed and Mazda did just this in '95.

Fuel and spark will have nothing to do with this problem. The ONLY way you get an engine to rev higher is getting air around the throttle plates, period. That's how the ISC works, it brings a metered quantity of air around the TB to set the idle speed. If the ISC was totally shut and the throttle was total shut with no leaks the engine would stall.

Oh, and double check your idle settings on the PFC. But, the PFC can only control the ISC for setting idle speed - if you unplug the ISC and the idle stays the same or only drops a bit, the ISC is either fine or is stuck open.

Dale

 

Thanks Dale.

I guess what I'm not quite understanding is why the idle will hunt and surge with the ISC plugged in, and when I pull it off the idle sits flat. I was expecting the same high idle as with the ISC plugged in and was surprised the value not only fell but was constant.

Also as I mentioned, with the ISC unplugged the car won't start properly unless the throttle is blipped. It will stumble around at 200-400 rpm and stall if I don't hit the gas. Is there something that happens after the throttle is hit, or am I giving the engine enough momentum by hitting the gas to exploit the possible vacuum leak?

I guess I have a few more things to try.

 

First thing you need to do is pressure test for any air leaks at all:

http://fighters-garage.com/rx7.html scroll to bottom

Is idle IG control on or off under function select? Datalogit logs would make this easier to troubleshoot. If the airpump is not engaged what is the idle AFR?

 

the ISC goes full open when you are starting the engine.



see this post in my thread: https://www.rx7club.com/showpost.php...4&postcount=34

 

Update:

Dale, good call on the PCV. That thing was totally shot and acting as basically a pass through between the oil filler neck and the UIM. I think I found a small boost leak as well by doing the pressure test, that will probably save me a headache when my break in is over. Everyone with an idle problem should do a pressure test! I'm sure that has been said a bunch of times before, but it picked up something I had no idea could be causing the problem.

I need to pick up some parts to fix the PCV, so I don't know if that fixed everything ... fingers crossed.

Idle AFR without the airpump is 12.6 - 13.4 ... so I guess I'm good there.

I'm thinking that the hunting and surging at first was the PFCs attempt at learing to idle with a large vacuum leak. Once it gave up it just figured 2000 rpm was as close as it needed to be. If I can't get the idle in line I'll post up some logs so you guys will have some idea of what is going on.

Thanks for the tips!

 

it's much easier to diagnose idle if we know

1) ISC duty

2) ignition timing (leading and trailing)

3) TPS voltage

all of which can be logged by selecting "advance" under the monitor window of the Datalogit FC edit software, and then taking a log