Idle Adjustment

Last updated: February 25, 2003

Correct idle speed is 850 RPM.


Date: Tue, 8 Jun 1999 16:51:50 -0400

Before we go adjusting the idle, something else is wrong. Idle is set from the factory, and unless you have major changes it should NOT, and I repeat, NOT need to be adjusted. Something else is wrong.

Possibly bad plugs, possibly bad coil. What other things do you notice? smoothe idle? popping? anything?


Date: Tue, 23 May 2000 21:12:24 -0400
From: "Sandy Linthicum" (

>...stalling when AC on at idle

I forget the name, but the stock air-bypass system effectively open up the throttle plates (ie allows more air flow to the engine) at idle/cruising when sensed load occur like AC, alternator, etc. If the ECU isn't seeing the load signal or the bypass isn't increasing RPM (or problem X) then the load will likely stall the engine.

Having a light flywheel make the problem very obvious.


Date: Tue, 23 May 2000 21:49:55 -0700
From: "Derek Vanditmars" (
Subject: Re: (rx7) [3] stalling when AC on at idle

What I have done to my car is set the Idle Adjustment Screw a bit higher in RPM that what the shop manual says to do, (with the TEN jumpered to GND). My theory on this is that the ECU initially defaults to the 50% duty cycle on the Idle Solenoid, then adjusts from there, (however I could be full of BS on this also).

In addition my Dashpot was WAY out of adjustment and not engaging until about 1,000 RPM, should be at about 2,800 RPM. After doing all of the above not stalls with the AC on anymore.

PS - I find that the Idle Adjustment Screw needs to be adjusted about twice a year, just before summer and just before winter.


Date: Tue, 8 Jun 1999 15:15:47 EDT

>Where do I adjust the idle speed?

You can adjust the idle from 2 spots;

1. Underneath the elbow, use a standard screwdriver

2. To the side of the TB, theres a screw that can manipulate the primary throttle valve


Date: Sat, 12 Jun 1999 14:51:58 +0200
From: "Bernd Kluesener" (

850 is the correct idle speed. The lower idle speed stated in the workshop manual only applies when you connect the TEN and GND terminals in the diagnosis connector - in other words when you adjust the idle speed. Connecting TEN and GND is necessary to temporarily disable the ISC (Idle Speed Control) system. When you set the idle speed to approx. 725 rpm using this method, it will jump to 850 the moment you pull the TEN-GND jumper.

Idle speed adjustment:

  1. bring engine up to normal operating temperature

  2. connect TEN and GND

  3. connect a tachometer to diagnosis connector pin IG- and a chassi ground

  4. make sure the wax rod operated lever completely separates from the fast idle cam

  5. adjust idle speed to approx. 725 rpm by turning the idle speed adjusting screw located UNDER the throttle body between the two 10mm cap nuts that attach the charge air pipe to the throttle body

  6. if the idle speed is too high with the adjusting screw fully screwed in (clockwise), unlock and turn (counterclockwise) the primary throttle stop screw to give you more adjusting range for the screw under the throttle body.

  7. while adjusting idle make sure the fans are not running

  8. remove the TEN-GND jumper and verify that the ISC system takes the rpm up to approx. 850


Date: Thu, 19 Aug 1999 07:50:38 -0500
From: "Westbrook, Chuck E." (

> Can someone tell me where the roller is supposed to meet the hash mark on
> the fast idle cam?  page F-79 of the small '93 shop manual shows 4 positions,
> A, B, C, and D and my car seems to be meeting it at point C when cold and
> when warmed idleing.  Is this correct?  Should the meeting points be different 
> when cold and then when warm? And how much is it supposed to separate from
> the roller.  Thanks in advance.

The "C" point (next to last) is to line up with the roller at 76F water/engine temperature. This is adjusted with the thin screw that touches the hot wax rod shaft. The last point, "D" is suppose to disconnect(no more cold idle) at a water/engine temperature of 140F(going from memory here, please verify). This is adjusted with the large flat head screw on the back side near the double throttle area.

I had idle problems when my engine was almost warmed up, and when restarting at a temp of about 150F. All was caused by a bad hot wax rod. I replaced the unit and aligned the cam per manual. This fixed my problems.

For the 76F, I set the house AC for that measure with a digital thermometer from Radio Shack, then let the unit cool overnight. For 140F, I placed a hose and funnel to the coolant line, and poured about 2 gallons of 140F water thru it.


Date: Wed, 23 Jun 1999 22:25:27 -0700
From: "Roderick Newstrom" (
Subject: RE: (rx7) (3) Idle Speed Hunting

(Editor's note: I added links to other parts of my site to Rod's post. --Steve)

I happen to have my service manual here by my computer, so I'll just pass on what it says relative to hunting idle (it has LOTS more to say about rough idle, but I'm reporting on only the hunting idle symptom). It's item number 28 on page F-194. The list of possible contributing sensors and controls is:

Page F-225 describes the troubleshooting procedure. It gives the following hints:

Their procedure for troubleshooting is:

  1. Check for service codes
  2. Check for strong blue spark
  3. listen for air leaks (my mechanic suggests spraying carb cleaner around... it will get sucked in and cause RPM surge).
  4. Check the PCV valve (blow through it in both directions)
  5. Check the ISC solenoid (the manual has you pull the extension manifold, unbolt the solenoid, ohm it out [~11 ohms] and replace it if it fails. This is stupid. If it was failing the resistance test badly, it should be reported by the ECU, and if it's stuck, it will ohm ok and just not work. You should be able to pull the connector and tap the solenoid with battery volts and ground and listen for a thunk... that's what I did, but I already had the manifold off for re-hose so it was easy :)
  6. Check fuel pressure (break the line, insert a pressure guage, and look for 190-220 kPa)
  7. Replace the ECU.

Having said all of that, I can attest to the fact that the manual doesn't cover all conditions (mine passed all the above tests). I could give lot's of advice beyond the above, but since mine isn't fixed yet (though I have high hopes for an injector to fail the test at RC Engineering), I hardly qualify as an expert. I'll reserve my theoretical musings for later.


Date: Mon, 14 Jun 1999 14:40:16 -0500
From: "Chow, Thom" (

I had a symptom where the car would smell very rich during idle. The additional fuel at idle was causing the car to idle poorly and occasionally stall or flood. The fix for me was simple. It was an adjustment of the throttle cable. I had pulled and tightened it too much throwing it off at idle. I simply adjusted the tension, and now my car idles fine with no more rich fuel smell.


Date: Tue, 22 Jun 1999 10:26:41 -0400

>Secondly, my idle is consistently high around 1300 rpms and if I
>turn the headlights or the fan to one of the higher speeds the idle
>increases to 2100 rpms.

The idle should be 750 rpm. 1300-2100 could be an intake leak past the throttle body. This is BAD. You must fix it NOW. Its not a plesent job. Figure about 10 hours labour for the easier part. Or 15 if its the lower gasket. An experienced place could do it in less (probably much less)


Date: Tue, 18 Apr 2000 17:46:38 -0500 (CDT)
Subject: (rx7) [3] update on high idle.

Thank you all for the advice. Those of you who mentioned that the LIM gasket was leaking were right. I went ahead and had the car taken to a rotary mechanic and it's being replaced!


Date: Wed, 2 Feb 2000 09:44:38 -0600
From: "Westbrook, Chuck E." (
Subject: RE: (rx7) [3] Unstable idle

It usually is a combination affected by the idle level (idle set screw and air bleed screw), TPS setting, and cold start system(hot wax rod and fast idle cam). Once had the same problem and it was the hot wax rod gone bad. When it was adjusted for cold starting, it did not release enough when warmed up. This caused the ISC system to try to reduce the idle beyond it's control. This caused the oscillations in the system. Sometimes just having the idle bleed screw open too much can cause the problem because once again the ISC system is out of range. These symptoms can be also caused by small vacuum leaks causes the imbalance.

No easy solution! Just have to check all.


Date: Thu, 10 Feb 2000 20:02:11 -0600
From: Steven Kan (
Subject: Re: (rx7) [3] Wild hunting idle - 1.5 to 3K RPM??

> Grrr.  I finally get my last little problem fixed and go out for a test
> drive. With the new mods, the thing winds up so fast in first that I'm
> having trouble getting my shift point down, and hit overrev fuel cut
> (again).
> Back at cruising speed, and the idle is ALL OVER the place.  Lots of
> popping and chugging.
> I know it's a vacuum hose, but didn't this just happen to someone?  If so,
> which one was it?
> I've checked all the visible ones, including the boost sensor.

Check and see if your EGR valve popped out or your fast idle valve got stuck. It sounds like you have a very big leak.


Date: Thu, 10 Feb 2000 20:45:43 -0600 (CST)
From: "Steven N. Burkett" (

> Check and see if your EGR valve pop out or your fast idle valve got stuck.  It
> sounds like you have a very big leak.

Steve wins the "lateral thinking" prize. Thanks for reminding me that not all RX-7 problems are vacuum hose related! ;-)

The problem was with the upper outside butterfly valves in the throttle body. (The "No. 2 Secondary" I think?). Anyway, there was black goo keeping them from closing all the way. Like oily carbon buildup. I can't say for sure.

What could cause this? I just had the throttle body off to change the wires a few days ago, and although it wasn't shiny-perfect-clean, the valves were moving freely.

Any thoughts? (Remember - I just did intake and exhaust mods, and the problem occured immediately after a full throttle run that ended in brief overrev fuel cut).

Anyway, it's clean now. And idling fine.


Date: Thu, 22 Mar 2001 11:57:44 -0800 (PST)
From: Chuck Westbrook (

My engine started having mild idle problems. Sometime it would die when stopping with the AC on. Sometime with it off. It was erratic. My ECU had been replaced with the AC fix years ago. I tried a new O2 sensor and adjusting the idle controls. It helped, but the erratic behavior continued. The O2 voltage read negative a few times. Then I started having erratic detonation problems but my J&S prevented damage. I turned my boost down from 12psi to 10psi and the problem went away. Being that my engine was using a lot of oil, I thought carbon buildup was the problem. I was running a XS ECU.

Then I got the PFC. Idle was OK now with no more dying idle conditions. Still had the detonation problems above 10psi. Added in more fuel but it really did not cured that. I couldn't tell what was happening by the plugs because they were always oilly carbon up.

Just installed a new engine. It idled terrible but the oil problem was gone. I started playing with the injector controls. Discovered that my #1 primary injector is running about 12% lean! All the injectors had been serviced by RC Engineering 1.5 years before the previous engine started having problems last summer.

Consider that the RX7 primaries actuate once per rpm where as 4 cycle injector does it every other rpm. My problem started at about 75,000 miles with a 8 years old car. That is equal to 150,000 miles and 16 years old 4 cycle engine. Luckily the secondaries don't get as much use.


Date: Tue, 4 Apr 2000 22:20:52 -0700 (PDT)
From: Jay (

> I was driving the RX-7 home today, when it started sputtering and stalled.
> It is an automatic. I them tried to start it andit finally started, but it
> is really sputtering and smoking badly. If I let the RPMs get too low it
> will stall sometimes. When it is just sitting in the srivway running, it is
> smoking and the idle is bouncing and the car is sputtering. Is this a sensor
> or something? It was working fine this morning. 

If a vacuum hose has popped off past the throttle body then your car would have a tendency to do this. I would check the vacuum hoses attached to the intake manifold, three on the front and two on the back. Plus the MAP sensor that is located on the back, which is what I had a problem with.


Date: Wed, 5 Apr 2000 06:56:17 -0400
From: "Gary C. Friedman, Psy.D." (

Have you checked to see if the MAP sensor hose popped off. I get the same symptoms in my manual when this happens. It is on the driver side, little black box by the firewall, with a hose that runs from it to the middle of the throttle body. If memory serves... the MAP sensor may be marked "MAP." If my memory is screwed... then it is the only small black box by the driver firewall with a hose coming out of the bottom


Date: Fri, 7 Apr 2000 15:51:22 -0400
From: Scot Kight (

Not at the hoses, check the intake system at and past the throttle body.

Before that you are just getting unfiltered air, or losing boost pressure. The actual air level metering doesnt exist (in a very basic sense, this isnt a MAF system) at all till the TB. You could have a bad old paper gasket between the TB and the upper air intake manifold. or your upper intake manifold could have a bad gasket, or god forbid, the lower intake manifold gasket. Start your car and spray carbcleaner on the gasket connection points, if the idle changes while spraying, you have found your problem. Do it while warming, but not hot. Hot... the turbo COULD ignite the carbcleaner (even though its not likely). anyway, thats not a good thing to have happen.


Date: Fri, 31 Mar 2000 23:05:54 -0500
From: Daegal Benedetto (
Subject: Re: (rx7) Re: Idle goes low when stepping on brakes

Aarroneous wrote:

> Umm... the guy who originally posted the question isn't on the list.  But if
> you guys are curious, it was the check valve coming off the intake manifold
> to the brake booster that started to melt.  There was a TSB on this item;
> the rubber being right on top of the turbos would start to deteriorate, and
> boost would leak into the brake booster which should only see vacuum.  They
> fixed this by replacing both the rubber tubes on the ends of the top hard
> pipe which runs along the firewall.  The check valve is now on the driver
> (US) side of the pipe.

On my '92 build it was on the drivers side so it must have already been replaced (brake recall?). I took the hose off and it took a lot of force to get the valve to open and close. When it did, it did so with a very distinct pop like a pop gun or the sound you make with your mouth. In my experience it seemed a little hard to get it to open and close but with nothing to compare it with I may just replace it to see if that cures the idle dip.


Date: Sun, 2 Feb 2003 18:13:57 -0800
From: "DVanditmars" (
Subject: (rx7) [3] Idle

(my) idle problems have now been fixed on my car today!

I fixed the clutch switch by replacing the spring, as mentioned by several listers. Permanently grounding the neutral switch was recently mention on the list as well. Thanks guys.

I think I have figured out the how and why of idle speed control for the RX-7.

The ECU needs to determine when to enter the "lean best idle" mode.

  1. It looks at the clutch status OR the neutral status to determine if the engine is connected to the wheels, (basically does the engine have a load attached?).
  2. It also looks at the RPM and if it is below ~1100 RPM.

If the ECU does not see the clutch in OR the transmission in neutral it will not attempt to keep the engine at idle speed. The ECU assumes you have control of the gas pedal, (and know what you are doing).

The speed of the car will solely determine the engine RPM, even if it goes below idle speed.

The ECU does not intervene with the Idle Speed Control valve.

This is why the idle will change with these problems, based on any electrical accessories being on, or the idle goes up when it is warmer out, phase of the moon, etc.....

I am not sure what the ramifications of having the ECU think it is in neutral all the time. From what I can tell, when the RPM is above ~1100, it is not trying to do the idle thing, thus it is just running the engine the way it normally does.

There may be some drivability issues, (if you ground the neutral switch) with the ECU fooling with the ISC when RPM is below 1100 with the clutch out. In stop-and-go traffic on a flat road where you go like 2 MPH with the clutch out and running below 1100 RPM the ECU will kick in the ISC and try to keep engine RPM at idle speed.

I will be replacing the neutral switch if I have to drop the transmission.


Date: Tue, 4 Feb 2003 18:30:15 -0800
From: "DVanditmars" (
Subject: Re: (rx7) [3] Idle IMPORTANT

I drove the car today and did some more O2 measurements while driving.

YOU SHOULD NOT DRIVE WITH THE NEUTRAL SWITCH GROUNDED OUT. The ECU thinks you are in neutral and if you give any gas you go VERY lean, especially at lower RPMs with a heavy load.

Removing the ground for neutral and the ECU goes to it's normal feedback loop up to about +3K RPM where is drops into the fixed maps.

Ed.'s note: in other words, don't do what is mentioned in the previous post. I just kept that for reference above, in case anyone is thinking of trying that. --Steve

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