Hi folks. My car has developed a really bad idle. i couldnt adjust it with the aac valve adjusting screw so fitted with a new iacv unit. still lumpy. ive checked all connectors and the one going to the ficd solenoid is only gettin a feed from ground side. ive traced it back to the ecu where its sending the feed and tried a known working ecu too which hasnt helped. it might be a broken wire somewhere in the loom. so ill need to try that. but also when i did a leak test there was a slight leak in the plenum. so my question is this, would the ficd cause the revs to bounce on idle and almost cut out or could it be the air leak causing this. it seems to be getting worse. before it was fine when driving but now its not driving right either.

Also is there anyone in the glasgow area who has a consult that could check it for me?

Thanks in advance

id get the plenum air leak sorted out first as it could be the gasket giving way, this would cause a noticable rough idle

id get the plenum air leak sorted out first as it could be the gasket giving way, this would cause a noticeable rough idle

 

Agreed...air leaks are a killer..... then check the timing and all the obvious things...

Done all of the above and still not fixed!! im ready to buy a litre of petrol and burn the goddam car!!

it will not idle at all now. if u give it a rev itll run with a slight misfire. ive checked plugs, coils injectors tps everything and im at a loss now. is there anyone with a consult as i cant do a ecu check as the bulb has been removed.

please help!!

You can do an ecu check with the led on the ecu itself.

yeah thats the led thats been removed! i tried another ecu with the led in and my immobiliser cuts the power to the ecu after 10 secs!!

how did you check for air/vac leaks and did you find any?

The engine management light on the dash does the same flashing as the led on the ECU mate...

Hi folks. My car has developed a really bad idle. i couldnt adjust it with the aac valve adjusting screw so fitted with a new iacv unit. still lumpy.

 

A lumpy idle and a low idle can be two different things, lumpy suggests poor spark, fuel or/ and poor combustion while too low a tickover suggests simple base idle issue.

 

the ficd solenoid is only gettin a feed from ground side. ive traced it back to the ecu where its sending the feed and tried a known working ecu too which hasnt helped.

 

If your testing and description is correct you have found the problem, unlike many cars Nissan decided to operate many things including sensors and valves by switching the earth /neutral side of the connection and leaving the live side on ignition switched, the +12v you are missing supplies the whole AAV unit, so the cold run, the ficd and the idle stabilisation need that supply without it you will not be able to acheive a regulated or stable tick over.

 

 

also when i did a leak test there was a slight leak in the plenum.

 

This does need to be sorted, if you mean the plenum you mean the gasket, if you mean something else attached to the plenum then thats a different job, any small pipe attached to the plenum leaking will more likely cause a slightly raised idle speed.

 

so my question is this, would the ficd cause the revs to bounce on idle

 

No, but bouncing on idle suggests the idle stablisation is working but is overworked due to too low an idle, getting some confliction there as you mentioned above there was no power supply?

 

almost cut out or could it be the air leak causing this.

 

Back to the begining here I think, you need to be sure there is a power feed, that AAV unit is a working one and try set the base idle higher first and then lower it to suit.

 

 

Also is there anyone in the glasgow area who has a consult that could check it for me?

Problem you have is that most peeps with ConZult do not know how to interperate it ( no offence guys) and a normal garage will just mess with the

settings to mask the problem, start again , use the wiring diagram available on line to check out your power supply issue.

 

http://www.300zx.co.uk/cgi-bin/manual.cgi

 

 

Thanks in advance

 

Hope that helps.

 

Jeff TT

Edited September 25, 201114 yr by JeffTT

Thanks for ur advice Jeff.

 

Its hard to describe the problem. when u start the car it struggles to start and ticks over at 500rpm and bounces to about 600rpm then eventually cuts out. if i adjust the idle screw nothing happens. it is a known working iacv and air regulator that ive fitted. ive checked the resistance on the aac and ficd solenoid and they are all fine. if i rev it to about 1000rpm it runs fine with a "slight" misfire. i checked the plugs and there was a slight brown colour on the tips which suggests its running lean. all coils are firing and all injectors working too.

 

i think u are right about the aav unit. when i disconnect the plug that goes to the aac on the iacv there is no idle change at all. which sounds to me as if the whole iacv isnt getting power. iirc its wire no 33 on the ecu, its the red one. i was going to try and run a scotch lock onto the wire at the ecu then connect it with a scotch lock onto the wire at the plug side to see if that works.

 

I also removed the entire plenum and checked for leaks, i then rubbed some sandpaper onto the plenum and inlet manifold to clean up some old insta gasket. Then applied a fine layer of insta gasket onto both parts to seal. my egr piping has all been removed before i got the car. ive replaced/checked all pcv hoses and hoses going to and from the aav and air regulator and balance tube. but i can hear a hiss coming from that area! which is p***ing me off. i have an smoke/leak tester at work which i used to do the test. great piece of kit by the way!

Thanks for ur advice Jeff.

ive replaced/checked all pcv hoses and hoses going to and from the aav and air regulator and balance tube. but i can hear a hiss coming from that area! which is p***ing me off.

 

The hissing noise from the air regulator and balancer bar will be due to the AAV not opening at the base idle screw section, this increases the air flow ( and sound ) through the air regulator.

 

I have a patch lead made up that plugs into the yellow connector on the top of the AAV with cables long leads for testing with a meter or to connect direct to the battery, if you do this with the engine running the revs should speed right up, if not the AAV solenoid is toast, you could always run a test lead power (fused ) to the aav cable, as I said the actual switching would still be done on the neutral / earth side, might be a quicker way than looking for the actual fault.

 

Jeff TT