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Discussion Starter · #1 ·
Do the turbos just naturally idle a bit rough?

I've been trying to clear up a rough idle on my 83T. It is the same problem I had with my old 82T. The mechanic says that the car runs perfectly -- that the straight-six turbocharged engines in all the 280 turbos just run rough by nature, and that there is no fixing something that isn't broke. I thought when well-tuned it should have a sewing machine smoothness to it. He said you could balance a quarter on a well-tuned NON-turbo engine, but not turbos.

Is this true?
I'd appreciate any input!
 

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Sounds like the guy isn't much of a mechanic. I have been in several 280 zxt that ran very smooth and accelerated nicely. My old turbo motor with mucho mods still had a nice idle, although the exhaust made it loud. I would say take your car to a different mechanic. There is no reason why your car should not run smoothly.
 

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My car has a similar characteristic. I asked the Z specialist in my area where my car should idle as it had dropped down to about 750 rpms. He told me that turbos fluctuate, but should hover around 900 rpm or so. This would not describe a miss though. My car misses in addition to hunting at idle. I have no idea what causes my intermittent miss, I'll take it to him when I get another vehicle to drive for a day or so. I recently replaced a restrictive cat back exhaust pipe and muffler on my car and my idle came back up to 900 rpm.
 

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My 82Turbo parts car was idling rough (hunting a lot but not missing) and low (500-750rpm) untill I pulled out the plugged up cat(fixed the lack of boost too). Then idle got more stable and smoother, although it still isn't perfect.

Perry
 

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Well Brian, as for my 81 it rumbles I mean idles roughly, too. My symptoms only are noticed when then engine is cold. Once the engine warms up to temp it returns to a mildly erratic idle. My problem is caused by other things than your car since I am in the process of revamping all turbo gadgets. You know the EGR tube on the turbos well mine is just open to the wind and sucking cold air into the intake like it should not.
Back to what could be your problem. I would not say the catylitc convertor unless your boost response is slow. I would look at either a bad head temp sensor, bad TPS sensor or bad thermotime switch. On the outside chance it could be the AFM,but highly un likely. I would first test all these pieces with an ohm meter first to make sure you do not waste money replacing a good part. E-mail me if you have further Q's.
 

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My car had a rough idle. The service manual says 750rpm at warm idle, 900 cold.
On top of the intake manifold is a bypass valve. This valve (the name of which has left me for some reason) has a bimetallic strip in it. When the valve is cold, it opens, allowing air to bypass directly into the throttle body. This aids in cold starting. When warm, it closes, forcing all air from the AFM thru the proper channels. 10 to 1 that valve could be bad. It will cause 1. a high idle 2. rough idle.
Another cause could be the EGR valve not closing all the way when the motor is warm.
Email me and I will send you a copy of the troubleshooting procedures for these valves.
I don't believe a turbo engine should idle rough by design. I could balance a quarter on my '81.
 

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> My car had a rough idle. The service manual
> says 750rpm at warm idle, 900 cold.
> On top of the intake manifold is a bypass
> valve. This valve (the name of which has
> left me for some reason) has a bimetallic
> strip in it. When the valve is cold, it
> opens, allowing air to bypass directly into
> the throttle body. This aids in cold
> starting. When warm, it closes, forcing all
> air from the AFM thru the proper channels.
> 10 to 1 that valve could be bad. It will
> cause 1. a high idle 2. rough idle.
> Another cause could be the EGR valve not
> closing all the way when the motor is warm.
> Email me and I will send you a copy of the
> troubleshooting procedures for these valves.
> I don't believe a turbo engine should idle
> rough by design. I could balance a quarter
> on my '81.

That funny thing on top of the intake is called an air regulator definately can cause wierd problems. There is no thermotime switch in turbos that I know of. There is another device on the throttle body that controls the idle speed by sensors instead of a screw. Check that too. I'd pick up a haynes manual it will make for easy identification of theses items and sometimes how to test it.

Sam 75 280z
 

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Re: Brian, you're not alone

> Do the turbos just naturally idle a bit
> rough?

> I've been trying to clear up a rough idle on
> my 83T. It is the same problem I had with my
> old 82T. The mechanic says that the car runs
> perfectly -- that the straight-six
> turbocharged engines in all the 280 turbos
> just run rough by nature, and that there is
> no fixing something that isn't broke. I
> thought when well-tuned it should have a
> sewing machine smoothness to it.
> He said you could balance a quarter on a
> well-tuned NON-turbo engine, but not turbos.

> Is this true?
> I'd appreciate any input!

Brian,

I have an '82 280ZX turbo with a somewhat rough idle. The car seems to accelerate fine. I have taken it to the dealer and two well known Z-Docs in northern California. Everyone tells me that's the nature of the car.

Here is what I have done to my ZX turbo; new Nissan remanufactured engine, new hoses, injectors, EGR, AAC valve, plugs, wires, cap, rotor, O2 sensor, AFM, throttle switch, coolant temp switch, fuel filter, fuel regulator, all EFI wiring, HKS exhaust, K&N filter charger. All this and idle will fluctuate 50 - 75 RPM's. Everything is at spec; emmisions, timing, fuel pressure, compression, vacuum, etc. All parts, other than exhaust and air filter, are Nissan. The only things I haven't replaced are the cat and ECU. The cat is not clogged, you would see that with a vacuum gauge. I can get about 10lbs of boost from my turbo.

I would put my knowledge up against anyone on this board when it comes to the the turbo fuel injection system. Assuming you don't have an air leak, and you've checked all the other common sources of problems, I've got to believe it is the nature of the car.

I've recently installed a Crane H-6 multiple spark ignition system with a Crane PS-92 coil, and low resistance plug wires. This made a significant difference. E-mail me if you are considering this set up. Best $250 add on I've made.

I suspect this car is set up to run very lean, my plugs seem to suggest that. I've even taken appart the AFM and adjusted the tension on the spring that enables it to respond a little quicker. This has some impact, but be careful, you can screw up your AFM if you release more than two clicks on this spring. I assume your idle CO was adjusted?

This is a long shot, but I am considering replacing the fuel pump with a high performance pump. I did notice my fuel pressure to be about two to five pounds low. But better mechanics than me tell me I'm crazy.

Let me know how you make out. I am very dissapointed with this car and the ton of money I've invested. (I could have bought a used 95
280ZX TT for the money I've dumped into my '82)

Good luck,
chuck

[email protected]
 

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Discussion Starter · #9 ·
Re: Brian, you're not alone

This is really depressing...

We replaced the Aux Air Regulator today and tweeked the AFM (1/2 turn) & TPS a bit. The AAR was supposedly bad, but I haven't noticed much of a difference.

The car doesn't miss, doesn't hunt and accelerates fine. It just kinda has a mild, slightly rough sputter that comes and goes while it idles. The mechanic still says it's natural, something like how a souped up V8 will sputter. But it just doesn't feel right to me.

I went over everything you guys suggested with the mechanic but he had checked everything out (the AAR had already been on order, but he had said it was only affecting the car when it was cold, and he appears to have been right). We did the other adjustments, but no improvement.

If anyone else has any ideas that haven't already been listed please let me know.

And thanks to all of you that did give suggestions -- they did help -- but maybe this thing really is incurable.
 

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Re: Brian, you're not alone

> My 83ZXT has over 165K on it and it also sputs a little on the idle. I disconnected the EGR valve hose, pluged it and this removed alot of the sputter.

One Z wizard told me that since it was a high milage car with no engine rework( i bought it new in 1982) that it's kind a like a old guy, just gets a bit cranky . He also added it could be from crank case blow by (worn rings and sleeves) even though the compression is still within specs on all cylinders. He said this puts this strain on the oil presure and this puts strain lots of other things.

My Z oil pressure at warm idle is about 30 on the guage. When running it is about 90. This suggests a little looseness in bearings and such.

I have resloved to let it run until it breaks and then we will fix it again.
 

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Re: Brian, you're not alone

> This is really depressing...

> We replaced the Aux Air Regulator today and
> tweeked the AFM (1/2 turn) & TPS a bit.
> The AAR was supposedly bad, but I haven't
> noticed much of a difference.

> The car doesn't miss, doesn't hunt and
> accelerates fine. It just kinda has a mild,
> slightly rough sputter that comes and goes
> while it idles. The mechanic still says it's
> natural, something like how a souped up V8
> will sputter. But it just doesn't feel right
> to me.

> I went over everything you guys suggested
> with the mechanic but he had checked
> everything out (the AAR had already been on
> order, but he had said it was only affecting
> the car when it was cold, and he appears to
> have been right). We did the other
> adjustments, but no improvement.

> If anyone else has any ideas that haven't
> already been listed please let me know.

> And thanks to all of you that did give
> suggestions -- they did help -- but maybe
> this thing really is incurable.

check out the fuel injectors, sounds like some of them could be clogged. Clogged injectors can cause unbalanced (sputtering) firing condition,
which by the way is most noticeable at idle.
 

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Check for a worn camshaft

> Check your camshaft because if your camshaft
is worn it will make the idle rough.

Do the turbos just naturally idle a bit
> rough?

> I've been trying to clear up a rough idle on
> my 83T. It is the same problem I had with my
> old 82T. The mechanic says that the car runs
> perfectly -- that the straight-six
> turbocharged engines in all the 280 turbos
> just run rough by nature, and that there is
> no fixing something that isn't broke. I
> thought when well-tuned it should have a
> sewing machine smoothness to it.
> He said you could balance a quarter on a
> well-tuned NON-turbo engine, but not turbos.

> Is this true?
> I'd appreciate any input!
 
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