My S6 FD RX7 has a problem when at idle. It nearly never sits still once the car has warmed up. It hovers up and down, constantly vary itself by 200rpm or so. It never used to do this. I used to have a constant, rock steady idle.

I have measured the voltages on the Throttle Position Sensor (TPS) and they match the ranges stated in the manual. Given there is no throttle movement at idle it would seem strange that something is telling the computer to vary the idle.

I have also noticed that when I turn on the interior fan, producing extra electrical load, the idle drops a little and stays rock steady.

I get no errors showing on the ECU.

Any ideas what's going on?

Thanks.

 

bump - Any ideas what controls the idle response when the car is running but stationary. The idle hunts up and down when the car is just sitting there.

 

I don't have any ideas for you but try searching for "idle hunting" or "idle surging"
There are tons of threads with lots of good suggestions out there already.

 

Ok, this problem is really annoying me...I've read as many of the threads as i can find and still no joy. I'm running out of ideas...

So far I have confirmed that the cold start bits of the throttle body are out of the way. At least the wax rod comes out about 1cm (is that normal or should it come out further than that???) and I've turned in the screw all the way. The roller separates from the cam when warm.

I've set the throttle body to ground zero by closing off the screw underneath the intake elbow and i've backed of the idle screw on the front of the trottle body so that it only just touches. I checked the TPS voltages at this point and they are within the ranges specified for both wide and narow range.

I have removed the ISC and cleaned it. As part of my diagnosis I actually unplugged it to see if the rolling idle stopped when the car was at a stand still. No joy.

I've sprayed carby cleaner around to try to detect any vac leaks, again, nothing there which kinda makes sense as the car boosts fine.

I've checked the fuel pump resistor. This checks out bt was suggested in another thread.

I've checked the clutch switch. Ditto.

I have a grounding kit to various places and I even wired an extra ground for the O2 sensor just in case it was giving a weak signal. The sensor itself is new.

The air pump is working and running at idle as it should.

The car has had new plugs and leads.

I swapped out the pressor sensor (because I have two of them) and there was no change to the idle at all.

I'm running out of ideas. Please help! I really need some advice from an expert who has worked through these problems before.

 

I wish I could help. I hate these kind of problems where the club isn't helping much! I'd offer some input, but the idle has always been solid on my FD and only the TPS has caused issues on my FCs.

 

The screw you adjusted under the TB is suppoed to be adjusted only after using the jumper in the diagnostics box. Assuming your RHD cars and ECU's are the same as the US models.

 

I have not heard of any procedure to adjust idle that uses a jumper in the diag box. What's that all about? Can you explain further?

Thanks,
Andrew.

 

Hey mate, hope this can help you out...

Taken from http://www.fd3s.net/idle_adjustment.html

Date: Sat, 12 Jun 1999 14:51:58 +0200
From: "Bernd Kluesener" (bklues@syskonnect.pp.se)

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

 

I want to elininate the ISC as a potential source/cause of my idle problem. I have already taken it out and cleaned it but I can't really confirm if it is working correctly - all of the time.

If I disconnect the ISC and I still have the rolling idle issue and I can't get the idle steady is it safe to assume the ISC has nothing to do with the problem?

Can someone please confirm if this makes logical sense?

Cheers,
Andrew.

 

i have a similar problem...my car just runs REALLY rich when i first start it at beginning of the day...i just dial down the fuel aboue 10% at idle on the PFS and it runs perfect...all the smoke and roughness goes away...then when its over 140F ill add back the 10%

 

You have not swapped out O2 sensors, or insure that the dashpot is not holding the idle open, or that there is an air leak, or that something else is holding the throttle open

Air pump + O2 sensor + manual idle adjustment + ECU adjustments for ISC & fuel = idle.

You have not mentioned if you have a stock ECU or other.

 

I had this same exact problem. It would surge only when stopped by about 200 rpm. I could get it to stop by tripping the E/L unit (eg. parking lights on, blower fan on 3 or 4, or A/C on) and therefore drove around with my parking lights on all the time like a douche bag. I had checked and recalibrated the TPS, cleaned the ISC, checked the brake booster check valve (since it was only when I had the brake on) and deleted every unnecessary thing I could think of to simplify the equation (double throttle, wax rod, fast idle cam, AWS) to no avail. The things that I did the day it quit were new gaskets (throttle body, UIM [it didn't even freakin' have one!], LIM), new check valves (they were the original ones and only semi-functional), and new hoses to replace some of the older worn out ones. Sorry I can't be more specific than that since I did all the work at once. My guess is that I had a leak past the throttle body due to a faulty check valve, hose, or gasket. I hope that sorta helps. . . .

 

Thanks guys for the replys.

The O2 Sensor is new. The ECU is stock. I don't believe the throttle plates are open at all. I've backed off all the adjustments and last time I took off the intake elbow it was clean. The trottle idle screws seem to make no difference to the rolling, surging idle no matter how they are adjusted they just raise or lower the idle but it still rolls.

It does also idle a little high when you pull up and on occasion drops down to 850 but most of the time it wil only drop to about 1000 - still rolls. If I give it electrical load it will pull it down, again still rolling.

Can anyone answer my ISC question above?

 

bump