My 83 280zx turbo A/T has a minor exhaust leak somewhere on the manifold.

I can't afford to have this taken care of right now, and I can certainly live with it as it's by and large unnoticeable after 5 min or so of driving. (until then there is minor hesitation).

The car also idles very low - between 500 and 750 rpm. Sometimes it will drop so low while idling that the engine cuts off altogether.

I'm thinking this may be caused by the exhaust leak i mentioned. As such, I'm aware that turning the idle speed adjustment screw wouldn't be the 'proper' solution to the problem.

However, given that I can't afford to take care of the exhaust leak, what I'm wondering is whether I'd be able to "cheat" a solution by upping the idle speed by turning the screw?

Are there any risks / downsides to trying this?


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Also one other question: the other day I noticed a screw missing around where the big hose from the radiator attaches to the main engine area. (pic attached). Could there be any noticeable performance issues caused by this missing screw?

Thanks in advance

 

the exhaust leak won't cause any serious running problems. it's quite likely that your low idle and possibly the hesitation are due only to a bad connection or two. do some searching to find what components could cause your problems, then clean their connectors. at least that's what i would do. and my car runs well.

 

Sounds like your cold start function isn't working if it's only when your motor is cold. Check the air regulator connection first. The missing bolt won't affect your Z's driving, it's there to secure the thermostat housing down so it doesn't leak coolant.

 

Thanks for getting back to me so soon

I'm pretty sure the exhaust leak is causing the hesitation - my z mechanic (Mark at Mike's Z in Whittier, CA) confirmed as much.

In any case I will definitely check all electrical connections when I get a chance - any particular connectors you'd advise me to focus on off the top of your head?

And failing that, is there any reason NOT to try counteracting the low idle by turning the idle adjustment screw?

Great...thanks lifegrddude. I'll definitely check that connection first It's mostly when the engine's cold, although the really low idle does seem to happen sometimes even after it's warmed up. Thanks for the info on the missing bolt too.

 

i'll just say, some mechanics are raging idiots. even z specific ones. mine told me to tighten my cam journals to 9 in/lbs. but, perhaps, if it is quite bad, i can see it possibly affecting the way that it runs

 

Deinitely agree with you there...I've had more than my fare share of idiotic experiences...however I don't have any doubts about this guy i mentioned

 

that hole that you say there is a bolt missing is actually left intentionally unbolted. no biggie there. ive never figured out what goes there, just that its always empty

 

Locate the air regulator on top of your manifold. Now when you first start the car up from cold does it fire right up or kinda stumble to life? Also what does the idle get to? Pinch off the hose from the air regulator to the throttle body and see if there's a change in idle, engine sound, or anything. Like was said your air regulator is probably toast not uncommon. On my 76' 280Z it used to have problems with nearly wanting to stall over the course of the first few minutes of driving and it wasn't bad but it would noticeably bog down some on acceleration until it warmed up. Once I replaced the Air Regulator it made a huge difference.

I'm not sure how I feel on the subject of an exhaust leak. I'd believe it can have negative effects on the way your engine runs, but it's not enough. I used to have a really bad exhaust leak, rear stud had broken off, and even when warmed up the exhaust leaking through made the car sound have a really rapid ticking, sorta sounded like a motorcycle. When I finally fixed it thinking it was the problem, my car still ran exactly the same. Turned out my CHTS was bad.

 

Actually it fires right up pretty well, but then idles too low and often drops out without revving.

Usually bounces up and down right at the bottom (500 to 750 rpm). Once it heats up and starts behaving it probably idles around 750.

Wow...sounds very much like the problems I'm having...will definitely home in on that air regulator and see what's going on Thanks for all the help...any recommendations on where to pick up a cheap replacement air regulator?

 

Junk yards if you have access to one. Otherwise, comparison shop with MSA, Black Dragon, Kragen/Shucks, ebay, and other places.

 

I presume I need a pair of pliers or something for this as it's a big fat hose right?

Anyway, in my foolish, pre-looking-it-up-on -a diagram poking around i manually pinched a small hose from (I think) the AAC valve (although it could have been the EGR).

When I did this the idle speed noticeably increased and became a little steadier...what do you think I should read into this?

Obviously, it would be helpful if you knew exactly what I was pinching...first chance i get to get under the hood with my Haynes' diagrams out I will update this post

 

I've had a bad exhaust leak cause a performance problem before...

I had an '82 toyota celica, the exhaust manifold gasket had all but disintegrated when the problem occurred. What happened was that the car bogged down completely, could not get power until the rpms got to 4k... Even then that power was still limited. (idled fine though)

Turns out what was happening was that so much exhaust gas leaked out that the O2 sensor was detecting air and was telling the car to run richer, much much richer... In fact there was so much unburnt fuel leaving the combustion chamber and burning in the exhaust manifold that you could see the exhaust manifold glowing red!

Unfortunately I am not sure how that would affect a turbo motor

 

My car stumbles to life... but first idle cold is about 1200 rpms and then idle warm is 800. (Occasionally it drops low and wants to die when cold) I also have cold engine /cold weather hesitations too on acceleration.

Am I looking at the same or similar problem?

(not wanting to hijack so I will start a new thread if mine is a different issue or use the search feature )

 

When the car starts up you should be idling around 1200-1500ish from a cold start in Neutral. That's pretty much the way mine is, and I have an 83' ZXT A/T as well.

You can pinch it off by hand, but pliers will help. Yes it is a big hose right on top. I wish I had a pic for you.

That sounds correct to me, you'd have been pinching off the vacuum line to the Auxiliary Air Control(AAC) or as other people like to call it Idle Air Control Valve. Anyway the way this thing works is that when there's vacuum to it, it's closed, and when there's no vacuum to it, it's open and allowing vacuum to bypass the throttle body to raise the idle. When the car is first started from cold, I'm not sure about warm starts the AAC should be open allowing air in to help raise the idle as well as the Air Regulator. So I'm thinking either you have a vacuum hose to it connected incorrectly or the VCM may not be functioning. Or if you did this when warm, that would be normal as warm idle it should be closed. The ECU pulses this open and closed until it achieves proper idle speed.


1200rpm at cold idle sounds correct. Sounds like the air regulator is working properly. You probably have a slightly different problem, if anything I'd say for you possibly a bad CHTS as far as the stumbling/hesitation goes. MY Z31 does this, it sometimes stumbles to life and sometimes fires up no problems. Once in a while it'll feel a little sluggish at cold, I'm getting a Cylinder Head Temp Sensoe(CHTS) code so that could be the problem as I've done an ignition system refresher. My 280ZXT when the CHTS went bad, I don't remember having idle problems, but my car would pop, sputter, and felt practically undrivable until it started to warm up.

 

So do you think that this means the problem is probably not with the air regulator, and with the AAC or VCM instead?

Thanks!

 

so there isnt spose to be a bolt there? wow... then whys my manifold leak in that exact spot? im so confused

and we are talking about the far right exaust manifold hole that seem to be missing a bolt right? dam im going to have to get pics

 

Just wanted to resurrect this old thread as this problem has got a little worse, and the colder weather has brought some new info!

It turns out that the car starts up and idles nice and high (c. 1000 rpm, where it should be), when the weather and the engine is cold.

It seems to be when the weather and/or the engine is warm that the car suffers from the really low (under 700rpm) idle, and subsequent intermittent stalling.

Does this provide a good clue as to what the problem might be.

Also, going back to the original question, even if it weren't an ideal solution, do you think I could cheat the problem away by adjusting the idle speed screw?

And if so, how on earth do i find the thing!? (Doesn't seem to be where Haynes / FSM said it would be)

Thanks!

 

There is no "idle screw" on the turbo models. It's computer controlled... which means it's a sensor causing the prob. As everyone has previously stated, check the air regulator / CHTS / AFM - sensors AND wires.

And what is the timing set to?

 

You can adjust the idle on the turbos, but you do it by loosening the nut that holds the screw for the idle stop. This is something I had to do to make my car idle properly after removing the VCV and AAC from my intake manifold. Otherwise my car would idle very very low if it idled. So I adjusted that to bring the idle up and now my car idles pretty well. Mind you this though was what had to be done to remove stuff. My car for the most part was running normally at the time.

 

their is an idle screw, its on the under side of the throttle chamber..
it hard to see, get a (mirror) to find it.

it has a locknut you have to break first, it takes two hands one to tighten the locknut back & the other to hold the adjusting screw or bolt still after ajustment. (mine was a screw) a friend I meet @ the local z club showed me this... the arrow shows the general area...

 

You can adjust that TB screw, but I guarantee it's not the problem (unless someone else messed with it before). It's set from the factory, and messing with it will only cause more problems. The only reason to adjust it would be like in duowing's case where his didn't idle well after removing the AAC valve.

 

Thanks for all the help guys.

I know it wouldn't be ideal, but given that the low idle is the only real problem with the car's drivability, it sure would be mighty tempting if this could be a cheaty solution.

I haven't been able to identify the actual source of the problem - is the fact that it idles properly when cold a clue to any particular diagnosis?

If i do adjust that screw, should it be done while the car is idling?

 

yeah it should be done while idling so that you can watch it and see where you want to stop. you won't need much. but really, it's just going to mask the problem and possibly bring up others. it's a good idea to just find the problem. it's not a very complicated system.

 

Again.......

Check the AFM & CHTS sensors and wiring ... and what is the timing set to???

 

I'll try to check those asap. I've no idea bout the timing...never meddled with it. Should I?