idle issue

thehybridsnail

New Member
hi guys

my car seems to be idling high around 1500 rpm. once warm it seems to go up and down? really confused by this. Any help would be great.
 

fubar andy

Moderator & N/W Rep
Staff member
Check the AFR, make sure it's not dirty.

Sometimes going for a good blast clears it out.

I found thins a few years ago when I had this issue.
 

PobodY

Moderators
Staff member
Check your dump valve isn't leaking. - When I had a Bailey valve in, it would leak under vacuum sometimes; unmetered air meant a high idle.
 

thehybridsnail

New Member
I have given it a good blast and still the same. If i don't drive the car, idle stays just over 1200 and no fluctuation in the revs, i can rev it and still sits there. Once driven and i stop it then starts to fluctuate. Could somebody list all the possible causes soni can go through them one by one. Thanks in advance
 

Hardy172cup

New Member
I found this somebody wrote if it's helpful to you at all.


Here's something I wrote for gtiroc about the common causes of high idle on Pulsars -

1 : IAS Idle Air Screw. Its part of the IAA ( Idle Air Adjust unit which sits under the right hand side of the plenum chamber ). Used for setting the base idle speed. Is a slotted screw on the side of the IAA and can be seen under the plenum chamber.

2 : AAC Auxiliary Air Control valve. Also part of the IAA unit, this is the main solenoid that the ECU uses ( in conjunction with the Throttle Position Sensor ) to regulate the idle speed. Looks like a round tube fixed onto the IAA unit.

3 : FICD Fast Idle Control Device. Also part of the IAA unit, designed to raise the idle speed whenever the engine comes under heavy load, ie, when aircon is switched on etc. Looks like a small round tube with hex shaped sides, screws into the IAA right next the AAC.

4 : IAR Idle Air Regulator. Sits underneath plenum, works like an automatic choke ( but just for air ). Always switches on whenever you start the car and works on temperature, cold means open ( higher idle ) and gradually closes when intake heats up ( 3 minutes or so ? ). It has a heater inside so will always come on whether the engine is hot or cold and gradually close over the 3 minutes or so. Looks like a small cone with a disc stuck on the end with a pipe on each side.

5 : Worn throttle butterflies / throttle housing. Air leaking past butterflies or leaking in through the spindles.

6 : Throttle balance screws. One screw on each intake, used to balance the four butterlies at idle, can cause high idle if all are adjusted too far out. Can be found on top of the throttle body next to the injectors.

7 : Vacuum ports. One port on each intake that is used with a vacuum guage for balancing the throttle bodies ( see #6. ) Should have rubber boots blanking them off but have been known to disappear... Found next to the throttle balance screws on top of the throttle housing.

8: Igniton too far advanced at idle. Should be 20' +/- 2' for a standard car.

9 : Throttle butterfly stops incorrectly adjusted. Stops the butterflies from closing properly. One screw for each pair of butterflies, usually sealed in place and a right beach to adjust

10 : Accelerator pedal / cable not adjusted properly. Butterflies not closing fully, similar to #9.

11 : TPS Throttle Position Sensor fault or maladjusted. Gives the ECU wrong indication of whether the engine should be idling or not, see also # 2.

12 : Blow off valve leaking. Allowing air to blow past diaphram under vacuum.

13 : Air leak from any of the 3 billion pipes that connect everything above. The pipes are all rubber and do perish over time....

14 : Inlet manifold gasket or Plenum gasket leak.

15 : Faulty Lambda sensor. Used to set the mixture to approx 14.7:1 at low engine speeds / loads. Can cause mixture problems and uneven idle. Can be found on turbo exhaust ( dump ) pipe, bottom left hand side of the engine.

16 : Aftermarket fuel controller set incorrectly. Can be a problem on Apexi PowerFC ECU's where the 'electronic' base idle is set too low for the actual 'mechanical' setting. Causes the idle to hunt and jump around as it tries to achieve an impossible target.
 

PobodY

Moderators
Staff member
I don't know that I'd go through them in that order, but it seems like a pretty good list.
 

Hardy172cup

New Member
I'm not sure who wrote the list originally, it's just something I stumbled across one day when looking up idle issues and I thought it was a handy list ;)
 

thehybridsnail

New Member
Thanks for the list, what order would you through them?? I have a new dv to try as this is the most simple to start with. Where would you suggest next?? Thanks again
 

PobodY

Moderators
Staff member
I'd start with the easy stuff first:
  • Vacuum/boost lines; are they all sealing? If you can't see anything wrong try something as simple as taking them off and putting them back on again; sometimes that's all it takes.
  • Ditto the various boots and caps on the nipples on the throttle bodies (including the PCV hoses if you've still got them). - These are a possible culprit since they've had oil vapour going through them and may be more degraded than other hoses.
  • Pinch the vacuum line going to the BOV, if you can hear the revs drop immediately it was leaking.
  • Before you take the IAC valve off, or play with any of the associated parts; try taking the idle screw out and blasting some throttle body cleaner in. - If it's all gunked-up and not operating correctly, that might be enough to free it.
  • If you've taken the idle screw out you're going to need to put it back in and adjust it; see if you can set the base idle correctly with that.
  • If you can test the base timing, do so. Otherwise, unless you've touched the distributor you can assume it's OK. - This may be an invalid assumption.
  • Look at the lambda sensor; is all the wiring attached? - It's hard to tell if the sensor is dead, and there isn't really a way of cleaning them up to re-use. I'd assume that if the car runs fine at low RPM the lambda sensor is working (you can always check that it's giving a sensible reading in "diagnostic mode II").
  • If you've got a multimeter, check the TPS is giving the correct voltage at the "closed" position and at "wide open". - The most problems I had with this were caused by my fiddling and setting it incorrectly.
  • There's not much you can do about worn butterflies, but it's probably worth checking that they are returning to the closed position at idle. - So that covers both the stops and the throttle cable.
  • Similarly, unless you've got the kit required to balance them all I'd ignore the individual adjustments.
  • Obviously if you've got some after-market kit like FPR, check it's actually giving the correct pressure.
  • How does the temperature look? Is it possible the ECU isn't seeing that the coolant temp has risen?
    Not really a way to check this without Consult or similar.
 
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