Okay, I'm starting to get low on my options left to try to fix my hunting issue. To start off, I never had any codes. Here's the list of what I've done:

new GM EGR tube and gaskets
new EGR gaskets (EGR is good)
new IAC
new MAP
new Plugs
new wires
new dist cap (by PO)
new dist rotor (by PO)
new dist electrical component (by PO, name slipped my mind)
new GM PCV valve
new metal vac lines
removed TB, plenum and PCV lines, and completely cleaned them from the EGR tube & bad PCV "yuck", new gaskets
new VC gaskets, plus cleaned VCs
new dist o-ring, plus dist cleaning
new Oil Filter
new Air Filter
new 5w30 Mobil1 oil
timing set to 10 on 1 and 4, balanced, while in drive, automatic
new O2 sensor
tested a TPS from BAM-BAM, no change

symptoms:

pegged Oil Pressure Gauge
Idle when warm will be at 900, slowly go down to 500, hunting between 500-2000 two or three times, settle at 2000 and rest back down to 900, rest there for a bit and start hunting again.

BAM-BAM mentioned something about a Air Temp Sensor? Can I test this in anyway? Also my Fuel Vapor Cansiter is pretty dirty. Alt belt will squeel when cold. From leaking VC gasket oil has leaked down to exhaust manifold and one or two gaskets have slight bubbling around them.

No 'visible' smoke, can someone please help? This is my first Fiero and I can't drive it, and I want to so bad!!! Thanks!

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Mark Matthews
'87 GT Fastback T-top

Hey Mark!
Sounds like you need to double check connectors, but I am suspisious of the EGR...
You say the EGR is good, but how do you know? Does it have NO leak from the exhaust to intake passage while closed?
And the diaphram has no leaks too?

If not the EGR, and you suspect the temp senders, (All are water sensors, I believe!), Then they should be checked...
Un fortunately, I don't have the values for the V6...
crash...

Read "wire service" in my cave......

In very short... There is a GM TSB... Hunting Idle... Check the charging system and wiring!

If the ECM has sh_tty power and/or grounds, then all sorts of things will be off. Including Idle!

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11-Sept-01, The day the world as we knew it ended.

Okay, read it. I'm not the best with electrical stuff. I know the PO or whoever worked on the car broke about every single lock tab on the electrical connectors. Anyone have the list of everyone I'd need for an 87 GT Auto?

Something electrical sounds about right, I fogot to mention that my voltage gauge is up around 16 all the time, no pulsing, just high.

Wouldn't you think that an electrical problem would cause a code tho? What's the point of have it if it can't.

I'll see what I can do about cleaning everything.

Fierowrecker ::

The diaphram is good on the EGR I don't know how to test is there is a leak from exhaust to intake... also I have a very high pitched whistle at my intake. I heard a 'slight' one on BAM-BAM's, but you can HEAR mine easy. May be that is a sign of the leak your talking about.

I need to get out and record my engine and RPM gauge so you can see exactly what it's doing, maybe tomorrow.

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Mark Matthews
'87 GT Fastback T-top

16V is getting high but you can't always trust dash gauges.

Take the thing someplace and have the charging system checked. many places do this free. they have a thing the wheel/carry to the car that tests the battery and alternator in place.

On my old Z-28 I had an alternator failure that never would have been noticed except for slight flickering of the headlights at idle. Something about a diode set went out letting A/C current bleed through. It made the car act pretty weird.

Have you tried resetting the computer? Take cable loose for 10 sec or more. Restart with defroster and a/c off and let it run until the coolant fan comes on. Then drive it from 0 to above 40, stop, do it again several times. This should reset it if this is the prob.

Phil

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GTDude
25 years GM experience

It would not suprise me a bit if GTdude is correct here (he usually is), but it took me more than a couple of times for mine to reset & the ecm to relearn the parameters it needs, and all I did was change the 02 sensor. I did the 0-45 mph thing twice & the idle was still erratic. Finally took it out on the highway & ran it like I normally do, for about 5 miles & it starightened right out. I'd get a voltmeter & check the alt, (or follow Ogre's advise) ,it may be putting out a lot more than indicated & that will fry all kinds of things.

Sounds like a vacuum leak. If you can I would hook up a scanner and check the IAC counts, my guess is the IAC valve is near completly shut at idle due to the leak. A condition such as this will typically cause the idle to hunt severely due to the manifold vacuum fluxuations at idle. This would also correlate to your observations when disconnecting the MAP sensor.

I would also check the MAT sensor, I noted some pretty severe idle hunting with it disconnected once.

[This message has been edited by 00lE (edited 03-11-2002).]

Bad timing could do this. I know you said:

quote Originally posted by Mark Matthews: timing set to 10 on 1 and 4, balanced,

...but I set the timing on my 86 GT with a flash gun and it ran like sh*t. Then I turned the distributor without the gun, listening for the smoothest idle and highest RPMs and I got it to run much better.

To check for vacuum leaks, get a can of starting fluid and spray it around the intake and upper plenum gaskets and vacuum hoses while the engine is running. If the idle increases signifigantly when you spray, you have a leak in that area.

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"Its a Fiero thing... Heck, even I don't understand!"

Timothy E. Smith
1986 SE V6 BACK ON THE ROAD AGAIN!!!!
1984 Coupe
1996 Ford Probe GT
1999 Chevrolet Silverado Z71
1975 Chevrolet ElCamino SS

Okay, I'm gonna see if I can sneek down and have the charging system checked. I know I'm missing the tension bolt on the alt, but the belt only squeels when really cold. I just gotta throw a bolt in.

But after reading a couple more post I'm think that my cat and/or muffler is clogged up, my cat rattles when I hit it. Probably from the cracked EGR tube and bad PCV. Causing more exhaust to run back into the manifold, making the loud whistle at intake. Also causing the MAP to act different when unplugged.

Is there a why to check/test the cat and muffler?

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Mark Matthews
'87 GT Fastback T-top

quote Originally posted by Mark Matthews: Probably from the cracked EGR tube and bad PCV

You have a cracked EGR tube and you are wondering why your idle hunts? That is a pretty damn big vacuum leak right there guy...

[This message has been edited by 00lE (edited 03-11-2002).]

quote Originally posted by 00lE: You have a cracked EGR tube and you are wondering why your idle hunts? That is a pretty damn big vacuum leak right there guy... ]

No, no, no... I change the tube with a new dealer one. I was talking about before that, from the old one being cracked.

No one? No way to test a cat or muffler?

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Mark Matthews
'87 GT Fastback T-top

Ok, then you are forgiven.

Clogged cat. converters usually effect higher rpm operation rather than idle conditions. You can do a back pressure test via the O2 sensor hole if you really need to determine a clogged cat issue, but if the cat. converter rattles I would just replace it. I would also have the shop pull the exhaust section from the cat back and empty the broken pieces of catalyst out of the muffler (thats where they usually end up).

Okay, thanks. I'm sure you guys are right on the charging system, something does seem right about it being at 16. I just gotta find a time to get it down to a place to check it.

Any help on changing the Oil Pressure Sensor?

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Mark Matthews
'87 GT Fastback T-top

warm up the engine, Remove your alt belt and see if it still hunts

How do I do that? It will start without the belt attached? I guess that makes sense, since it's drawing the power from the battery anyway. Cool, I'll give it a shot, Thanks!

I'm think I'm gonna see if I can find another EGR, just to test it again.

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Mark Matthews
'87 GT Fastback T-top

You really would not need to remove the belt, just unplug the electrical connector on the alternator after you start the motor.
IMO, its not the cause of your idle problems, but I guess it cant hurt to check.
I will restate that you should check for vacuum leaks, as that is a primary cause of idle problems on the Fiero V6.

If the idle variations seem to occur at specific intervals, then it could just be the EGR status test/fail loop causing the flucuation. Start the car cold, and let it warm up fully without applying any accellerator at all. If it does not flucuate as it did before than that was indeed the problem, and you would obviously have an EGR system failure of some type.

[This message has been edited by 00lE (edited 03-12-2002).]

So how does that work? Once you apply the accelerator, that tells the computer or something to kick in the EGR? I'm not too up on the computer cars yet.

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Mark Matthews
'87 GT Fastback T-top

The ECM will not initiate the EGR status test until the engine has fully warmed up (closed loop) and the TPS has moved a certain percent (increase RPM) resulting in about 2500-3000 rpm increase at least once.

Once the test has initiated, if the ECM does not see the change in values from certain sensors (change in MAP, etc.), the test fails and the ECM will continue to loop the test at a specific interval until the conditions are met (e.g. forever). Note that during the test execution, the ECM opens the EGR valve a certain percent and adjusts fuel and timing accordingly (this value is a constant set in the code commonly referred to as: Egr Diagnositics Retard). This will result in an RPM flucuation if the correct amount of EGR gasses do not enter the combustion chamber during the test.

A failure of this status test will generally not set a trouble code unless considerable highway driving has occured with multiple test failures.

[This message has been edited by 00lE (edited 03-12-2002).]

Cool, I'll give this one a shot too, once I get off work.

Thanks again, I'll let you know.

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Mark Matthews
'87 GT Fastback T-top

I believe it to be fairly important to check for this condition on a cold engine (overnight cold if possible). If the engine is anywhere near cold closed loop operating temperature, the initial rpm burst from starting the engine may be enough to initiate the diagnositic test loop. Although I am not positive that this would be enough to initate the diagnostic, its still best to remove as many varibles as you can.
Pulling the battery cable for a bit to reset the ECM prior to the test may also be a good idea.

[This message has been edited by 00lE (edited 03-12-2002).]

Just what exactly are you resetting when you unhook the battery? This computer system doesn’t have an adaptive strategy built into its program. The only thing you do is clear the codes if any are stored. I didn’t think GM used adaptive strategy in its Pontiac division until the 3800’s were used

I think I might have figured it out!

I tried what OO|E said, starting it without any help. It had been sitting for about 24 hours or more without running so it was cold. It fell flat on it's face twice and then I got a code 34. Changed the new MAP with the old one I had, and thought I had it, but it started hunting.

So I was gonna try unplugging the alt, but thought os something else to try real quick. So I started the car, made sure it would hunt, and then cranked the AC. Damn thing wouldn't hunt, the amp gauge with down to 14-15. As soon as I turned off the AC, right back to hunting!

I tried unhooking the battery and retrying everything, the only time I could really get it to stop was to tuurn on the AC. I think ogre has it right with my charging system.

I don't doubt the my EGR could be bad also. But this is definatly a sign of electrical, right?

Thanks you guys, I'll try driving it down to a place on Saturday to have the charging system checked.

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Mark Matthews
'87 GT Fastback T-top

A code 34 with a known good MAP sensor is a VERY good indication of a vacuum leak. The code set due to unacceptable manifold vacuum (due to leak) rather than a defective sensor.
The reason for the vacuum leak could be anything from a bad gasket to a loose IAC valve. Perhaps when you raplaced the IAC valve you did not get to sealed adequatly??

[This message has been edited by 00lE (edited 03-12-2002).]

I wouldn't doubt that. That was one of the first things I did, who knows if I did it right.

I read the IAC thing in the cave and did it that way, but I did get an aftermarket, not an ACDelco. To be honest with you I never got an IAC code either, I just changed it cuz people said that was for sure the cause. Now my son pulled the pintle outta the stock one and I can't find it in the rocks! Any one have one they want to send me?!?!

I'll try the charging system real quick just cuz it's free, then I'll go from there.

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Mark Matthews
'87 GT Fastback T-top

[This message has been edited by Mark Matthews (edited 03-13-2002).]

Most aftermarket IAC valves are not that bad, I have used a few before with success, but I do prefer genuine GM. The problem is that the threads on the valve do not seal, and the gasket is useless unless the valve is torqued down pretty tight, which is not an easy task without the proper sensor socket. A very thin coat of sensor safe ATV sealant applied to both sides of the gasket will usually help in obtaining a better seal.