OK - heres the symptoms.....

 

uneven idle - revs stay around 750rpm but idles rough.

No hesitation

Fuel economy is fine

No loss of power.

 

Changed fuel filter

cleaned throttle bodies

replaced spark plugs

when removing each injector connector - engine note drops, then picks back up when plugged back in

ditto for the coil packs.

sprayed carb cleaner into idle unit.

 

none of this has made any difference.

 

Was going to squirt wd-40 into idle unit in case its got sticky. But I'm out of ideas at the moment

 

The car runs perfect off idle, its just when it comes back down.

 

Any ideas welcome.

My NA does the same now and then, I suspect it's one of the several hundred vacuum hoses leaking.

Have you checked the Throttle body senser connector (black box on passanger side throttle body give the connector a good clean. Or give Andy Duff a call he's in your neck of the woods

TPS has been checked - Been to Andys twice as he's only 15 mins away and theres nothin obvious going on - conzult checked out fine - one thing that does need doing is the passenger downpipe has a hole in it and needs replacing - dunno if that can cuase rough idle or not - O2 sensors check fine.

Have you checked the EGR? A build-up of carbon can cause a vacuum leak to the EGR Valve. There should be NO EGR at idle. Or

 

Check the PCV Valves are working by placing your finger over the opening (with engine running). You should feel vacuum on your finger and when released the valve should snap shut. If you can hear a hiss then it might be blocked or need to be replaced. Also, remove the valve from the tube an shake it. It should rattle like there is a loose marble inside. If it doesn't rattle, its blocked, replace them or clean them out.

 

A clogged cat can cause idle problems too.

 

Also the MAF sensor can get contaminated but not enough to set off a fault code, try and borrow one to try. Also cleaning the ECU temp sender can cure rough idle, thats what i found wrong with mine when it idled rough.

The MAF sensor is worth a look - temp sender is fine and clean.....I think it might be something electrical as this appeared while idling and hasnt gone away. I can clean the MAF sensor and hot wire with some carb cleaner.

it runs rough in what way ?

 

misfire ? stumble ? it just "sounds" rough ? or can you actually feel it ?

 

-does it still run rough if you increase the base idle rpm a little bit (+100 rpm)

-did you check/clean the connector of the AAC ?

-is the timing 15 BTDC on idle (check this using a timinglight)

-disconnect both O2-sensors (one at the time) and see if it improves anything.

 

also it may help to follow the procedure as described in the SM:

http://300zx-twinturbo.com/cgi-bin/manual.cgi?list=efec&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=67&design=default&total=190

http://300zx-twinturbo.com/cgi-bin/manual.cgi?list=efec&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=68&design=default&total=190

Theres a definate struggle for the engine - you can feel it vibrate even though the revs seem respectable. It literally started doing while I was in traffic a couple of weeks ago and it hasnt cleared up.

 

Andy checked the timing and o2 stuff on a Conzult and all looked ok - but I havent tried cleaning the idle connectors - I cant turn the screw to adjust the idle as the battery is in the way and the angle for the screwdriver is too steep. crappy design.

 

I'll have to try and rig up a boost leak gizmo and see if I've sprung a leak somewhere.

what fuel have you put in it? It may sound stupid but bad fuel or a different grade of fuel can make these cars play up. Another thing is re setting the ecu if you havnt already tried it, dissconect the battery over night and put some decent high octain fuel in

I was been having the same problem over the last couple of days so I thought I would try some of the advice above. Went to disconnect battery terminal and found there was no need for a spanner as it was hanging off already.

Checked Throttle body sensor which looked ok until disconnected, connections were all green. Same with PTU and temp sender, every thing cleaned and reconnected tightly. Going great now will keep my finger crossed.

I'll try and get to all the connectors...

temp is fine as new plug on it.

but will work through all the others just to be sure they are done.

bought some carb cleaner to help out as well!

Andy Duff has been a star and will be trying a few replacement parts just in case somethings packed up like the CAS sensor mucking the timing up

 

On the plus side I'm not down on power as I had a good blast with a 350z and was quicker than him on the M6 yesterday. Fuel consumption is also not affected as a 270 mile trip has used 2/3 of a tank which isnt bad.

 

Cheers for all the replies guys.....

Found the problem, a split pipe, the one that comes from the idle valve to the balance bar - part code - 14860NE - Mr Duff is a star - he had a spare on a plenum leaning against his garage and even though he's not about still said I could go and get it and use it! Hows that for being helpful! Anyhow - I now have a nice steady idle again.