Strange idle speed

[silver280zx]

i have a problem where the engine will idle between 800rpm and 2k, its very inconsistant, but not a big deal, and ideas?

[Gollum]

Does it fluctuate constantly?

How fast?

What conditions?

Is the engine cold or warm?

Or both?

Difference between cold and hot?

 

Could be tons of different things, the good news is that the stock ECU sucks at controlling idle, and I question if it's even able to. This means it's got to be a sensor, or inconsistant fuel or air.

 

I had a 280ZX that had an AFM with no air temp sensor, so when it was cold out it had a hard time starting and would idle terribly, but once the engine was warm it was better, and in warmish weather it'd start just fine (anything above 50 degrees basically).

 

Something these cars are pretty well known for is their bad electrical connections. When they're clean they work great, but often they get dirty and corroded. I'd clean them all up and the start checking for mechanical issues like the throttle return spring and such.

[silver280zx]

Its really wierd, when the engine is cold it tends to idle higher, that part is due to the cold start valve, but sometimes it doesnt idle down. One time i drive it, it will idle at 2000, the next coule be 800, then the next it could be 1600, or 1200rpm, i have noticed that it tends to idle a little higher when its cold out, but when the engine is warm, the idle problem still happens. It also doesnt like idleing down when i drive.

[nando280zxt]

Hmm....i dunno. My 280zx had the same thing as gollum, it would idle horrible and buck in the cold until warm. Head temp sensor swap did it for me though. Anywho. Does it fluctuate? Is the cap and rotor ok? Make sure its nice and snug. Dont think its that, but if its kinda loose that's do all sorts of things to you idle. Maybe you have vaccum leak? Electrical terminal corrosions. Id check those first

[silver280zx]

Hmm....i dunno. My 280zx had the same thing as gollum, it would idle horrible and buck in the cold until warm. Head temp sensor swap did it for me though. Anywho. Does it fluctuate? Is the cap and rotor ok? Make sure its nice and snug. Dont think its that, but if its kinda loose that's do all sorts of things to you idle. Maybe you have vaccum leak? Electrical terminal corrosions. Id check those first

ya everything with the ignition system is new, no vacum leaks, good fuel pressure. im kinda stumped, i could see how the afm could be a possibility though, i have a new ecu as well.

[Gollum]

Is the ECU from the same year? I know the turbo engines changed ECU tunes every year, and there were other minor changes. Maybe you put an ECU in that uses some different spec sensors?

 

The AFM itself shouldn't be a problem, but it does have an air temp sensor inside of it that can cause some issues if you're not getting signal from it. Overall the AFM is a very mechanical unit that's pretty straight forward. Might be worthwhile to pull it out and take the cover off and check to see if the contact points are overly worn.

 

Does it perform as variable as the idle? Or does it seem to always feel the same under accel no matter what?

[DuoWing]

Here's a few things you need to check. Check the Air Regulator to make sure it's closed all the way when warmed up and not leaking air. I've purchased newer air regulators, 2 now that have both been faulty and leak when closed.

 

Also I don't know if it's a Turbo or N/A, but I've read many people having problems with the N/A BCDD going bad and causing idle issues.

 

As far as a Turbo goes I used to have bizarre idle problems until I found out that I didn't even have the VCM vacuum lines routed correctly. Later I found out that my AAC valve although worked, it was going bad that when shut it would still allow air through putting the idle up higher than it should be.

[83zed owner]

is it normal on a n/a when it's cold to start at 2,000 rpm?????

[woldson]

83zx n/a dose for a short while.

[83zed owner]

ok thanks just wanted to make sure.

[nbesheer]

My 83 NA idles at 1k for a little while, and never above. and the car has been garaged for the last half of it's life so it might be safe to assume that that is normal ?

[roger.svoboda]

if you are sure you have no vacuum leaks (pull the oil filler and it should run worse) you might try reseating the connectors in the ecu and the afm. clean em up if you see some corrosion. eletrical connectors on cars old enough to legally drink start to get dicey. It always suprises me that they do keep on keepin on. Might be worth checking on battery condition (load test at a reputable shop). check battery cables for corrosion and clean both ends. If you have one of those clamp on connectors that people use to replace the original factory get some good cables. ZX are real sensitive to voltage. you can have enough to turn the starter but not enough voltage to run the ecu properly. Check your ground it originally went from negative post to a bolt beneath the battery box and thence to the starter. some get cut off and they run direct to starter but this eliminates a good ground point to the frame. i run a 10 gage wire from negative post to both sides of engine compartment to play it safe on grounding. Remember lucas prince of darkness got that name for insuffient earthings as the limeys say.

[silver280zx]

if you are sure you have no vacuum leaks (pull the oil filler and it should run worse) you might try reseating the connectors in the ecu and the afm. clean em up if you see some corrosion. eletrical connectors on cars old enough to legally drink start to get dicey. It always suprises me that they do keep on keepin on. Might be worth checking on battery condition (load test at a reputable shop). check battery cables for corrosion and clean both ends. If you have one of those clamp on connectors that people use to replace the original factory get some good cables. ZX are real sensitive to voltage. you can have enough to turn the starter but not enough voltage to run the ecu properly. Check your ground it originally went from negative post to a bolt beneath the battery box and thence to the starter. some get cut off and they run direct to starter but this eliminates a good ground point to the frame. i run a 10 gage wire from negative post to both sides of engine compartment to play it safe on grounding. Remember lucas prince of darkness got that name for insuffient earthings as the limeys say.

 

Ya ive done all that, the car is a 79 na, no BCCD i believe, its a january, so its almost identical to the s30 280z motors. This is a no cat, or oxygen sensor model. when the temperature is warm outside, the engine idles fine.

[jmmorriso]

does it have AC? maybe the idle up valve is sticky.

[Zedback]

My 1979 NA had been idling erratically between 1500rpm and 2000rpm with the idle speed screw all the way in. Are you sure there is no BCDD hanging down under the throttle body, because I've just removed mine and plugged all the holes. It's now idling at a rock steady 800rpm.

Note that it is an Australian car and specs may be a bit different.

[silver280zx]

Ok, there is a bccd, but now that its warmed up to 50-70's outside, it idles at 800rpm.