Idle chat

martin.herwitson · #1 25-05-2007, 21:13

Can anyone offer some advice? I'm struggling. Silvias idle speed has increased and now runs about 1000rpm, If I simply adjust the tickover then its too low when the engine is cold? I have tested the air control unit (choke?) as detailed in the manual...o.k. tested the engine temperature sensor...o.k. I have noticed that switching on several electrical items, lights, heater & rear screen heater causes the rpm to drop and I'm sure there should be some automatic compensation for this but I can find no mention of such a unit in the service manual and I can't think of anything else that would increase the idle like this?

any help would be appreciated.....Marty

s13eater · #2 25-05-2007, 21:18

the iaa unit where you alter the tickover has the voltage compensator in it, could you have an air leek ?.

30psi · #3 25-05-2007, 21:57

There is an adjustment screw for the pickup from when air con is turned on, might be an idea to see if this helps. Not sure if it switches on with the lights though.

Its probably an issue with the air regulator, prob needs cleaning. The S12 should idle at about 1,300rpm for about 30 secs when cold and slowly drop to about 8-900rpm when hot.

s12Rob · #4 27-05-2007, 12:31

mine i think has an issue, start up from cold, idles about 500 rmp then picks up once hot to abuot 750. any ideas

PukkaSilvia · #5 27-05-2007, 19:14

A good idea is to start your own thread rather than making this thread confusing with 2 different cars and problems.

30psi · #6 27-05-2007, 19:16

Its the same problem though? Low idle when cold.

martin.herwitson · #7 27-05-2007, 21:16

Hi Rob,
you seem to have the same problem, I have found that my air regulator is sticking. If you pinch the outlet pipe of the regulator closed (highlighted with red arrow) when the engine is cold then the rpm should drop (possibly 250 rpm) if it makes no difference then the air regulator must be stuck closed. Mine is sticking open resulting in a high tickover when warm, hope this helps. The yellow arrow is one of the "idle up" solenoids but I have no wiring diagram and don't know what energises them? On my car with no air con they seem never to operate?

30psi · #8 28-05-2007, 01:13

There should be a grey plug which plugs into the top. You can't see it in your pic its hidden behind a pipe. But on the top of the stem of the air regulator is where it connects to.

Sounds like they're both shut, but because you have adjusted your idle to be correct at cold idle, it will be too fast when hot. If it was adjusted to the correct speed when hot, then you would suffer low idle when cold like Robs.

However if it was working, then when its cold the air regulator is open to increase the rpm by up to 700rpm from experience.

I've only had one that worked really well. It seems they seize after a while. The way they work is fairly simple. There is a bimetallic strip which should open it up when cold. When the engine is started there is a current passed into the bimetallic strip, so when the strip is heating up it shuts the valve.

northerner · #9 28-05-2007, 15:44

I've just bought an 89 BB Turbo and it has exactly the same problem. I have taken off the Air reg and noticed that the slide inside does move when pushed with a screwdriver though. I suppose the only remedy is to swop it with another known good one. I havent got my manual, does anyone know were the feed comes from ie ecu or relay ?

martin.herwitson · #10 28-05-2007, 19:35

The feed is from the eccu timed same as fuel pump. Its a current device and draws about 250mA @12v but probably a continuity test is good enough to show that the heater element is working (continuity should exist) I have fitted a unit off a scrap yard car which is better than I had but I've been unable to find a new one?