Hi idle, loud hissing noise under air cleaner (Page 2/3)
gregr75 MAR 09, 06:25 PM

quote
Originally posted by Patrick:

make sure the hole in the air filter canister is plugged.




Yes, i double checked and it was properly capped the whole time.



quote
Originally posted by 1985 Fiero GT:

The reason the idle went to 1000 and was lumpy, with no hissing when the IAC was disconnected



Actually, I got the lumpy idle around 1000 after cleaning the throttlebody and IAC port hole and installing the air filter and everything but still had the IAC valve connected. I removed it afterwards to investigate it.

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87 GT Stock 2.8L

1985 Fiero GT MAR 09, 06:59 PM

quote
Originally posted by gregr75:


Actually, I got the lumpy idle around 1000 after cleaning the throttlebody and IAC port hole and installing the air filter and everything but still had the IAC valve connected. I removed it afterwards to investigate it.





Ok, have you driven it yet, above 35mph, and let it warm up, both of those conditions need to have been met before the idle will be where it is supposed to be, if it remains lumpy after that, there are a lot of potential things that can cause that, usually more on the sensors and vacuum systems, ex. TPS sensor could be just out of range enough to need the ECM up, but not so much that it generated a code, or the big one I found were vacuum leaks, if there's a vacuum leak, that means no matter what the ECM does, it can't fully control how much air enters the engine, which confuses it and ends up modulating back and forth.

The reason it needs to warm up is 2 fold, the ECM likes the engine to be warm before getting the idle perfect, and the oil can be a thicker consistency when cold, and it may not all thin out at once, on the odd occasion my Fieros idle gets lumpy, the oil pressure gauge will closely follow the rpm, pressure increases for some reason, making more load on the engine, rpm decreases, ECM sees that and adds air as oil pressure decreases, leaving less load on the engine, and more air/fuel then rpm increases, ECM cuts air at the same time that oil pressure raises again from increased rpm, etc.
gregr75 MAR 09, 07:55 PM
I haven't gotten the car back on the road yet, I need to fill it up with more coolant, and button up some other things to get it roadworthy. Probably in a couple weeks. Also I have to figure out how to reinstall this IAC valve and retract the pintle if possible. i do see some threads about partially putting a finger over the iac port hole while running to trick the iac pintle into retracting.

My car also has a parasitic electrical draw, so I was disconnecting the battery everytime i walked away from the car but now have it on a battery tender so the ecm can keep any codes that come up.

[This message has been edited by gregr75 (edited 03-09-2024).]

Patrick MAR 10, 01:03 AM

quote
Originally posted by gregr75:

My car also has a parasitic electrical draw, so I was disconnecting the battery everytime i walked away from the car...



Have you disconnected the single wire that goes to each headlight motor? That usually eliminates the parasitic draw in a Fiero.
Vintage-Nut MAR 10, 10:05 AM

quote
gregr75::
Previous owner did a crude EGR delete {and} I have heard of other people just letting that solenoid hose dangle there because it's just ambient air right?


With a stock system, 'Outside Air' is not 'Ambient Air ' when the engine is running.
This air input before the air filter housing input is lower than atmospheric pressure or a.k.a. 'vacuum'.


quote
My car also has a parasitic electrical draw, so I was disconnecting the battery everytime i walked away from the car...



BTW
My experience with a 'weird' parasitic draw issue:
I got a parasitic electrical draw when (a) the engine/trunk deck was open and (b) the parking brake was 'Off' as I was working on the engine and the brake system.
With the trunk light bulb out, current will still flow even though the ignition is 'Off" which will drain the battery.

Because the deck was open for months for engine service and a complete brake system service - my temporary 'fix' was to disconnect the trunk solenoid connector in the engine bay which stopped the battery drain.

I didn't dive into the circuit and added 'Check Factory Inline Diode' on my list to see if the diode is shorted or not.......

[This message has been edited by Vintage-Nut (edited 03-10-2024).]

fierogt28 MAR 10, 11:51 AM
The small rubber hose going into the air box that runs along the firewall to the passenger is for the hose we were talking about earlier, the EGR solenoid.

Both of my 88GTs, have them removed. I never had an issue for performance, and even the SES light coming in.

I did replace the EGR solenoid with a PFF member that had them refurbished, and my SES light never came on for an EGR related issue.
I have Rodney’s SS vacuum line kit, new EGR valve and tube.

My other 88GT is an original car, and that hose to the EGR solenoid was already off and not even on the car when I bought it.
The recall was done with the proper caps and hardware that GM supplied.

Jelly2m8 is the one who first told me about the hose for the EGR solenoid, so I give him the credit for educating me on this.
He mentioned that he removed / removes them also.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

Raydar MAR 10, 01:19 PM
The thing about that small hose (or even just the fitting on the end on the EGR solenoid) is that it sucks in air.
When the EGR/solenoid is not active, it switches the ported engine vacuum to "atmosphere" (aka "that hose"). It isn't "vacuum" all the time, but when it is, it can suck in unfiltered air.
(If you block that port off, it effectively just connects ported vacuum straight to the EGR valve.)

If that matters to you, find a piece of foam, and make a blind hole in it, small/deep enough to allow it to slip on to the fitting on the end of the EGR solenoid. Maybe glue it in place, in a manner that doesn't block the fitting.
Or you can take a hose and connect from the fitting to a small (lawnmower type?) fuel filter. Just a thought.
I really doubt that it can suck in enough dirt to do any damage, but it's worth consideration.
Patrick MAR 10, 03:50 PM

I don't understand the problem some people have connecting a short rubber hose from the EGR solenoid to the small metal tube on the firewall. Pontiac designed it that way for a reason, overwise they would've saved a nickel and not bothered with it. The recall eliminated the need to use the large metal tube on the firewall, not the small one. It's there, why not use it?
gregr75 MAR 14, 12:17 PM
Ok I'll probably hookup the EGR solenoid hose the way Pontiac intended…

I'll chalk up the loud hissing noise to an IAC valve that was stuck open (retracted position) I can't find any other explanation it went away after I sprayed the whole throttle body area with carb cleaner.

However In playing with the valve and experimenting with it, the spring and pintle went flying out and I ruined it trying to put it back together.

I just received a new IAC valve, The pintle sticks out less than 1 1/4" The Pontiac service manual says "
No physical adjustment is made to the IAC
assembly after installation. IAC resetting occurs
after reinstallation on the vehicle, and is
controlled by ECM action when the vehicle is
operated."

So, why do some people perform a "reset procedure" by jumpering the ALDL after the IAC is installed. I guess I don't understand the purpose of it if the IAC valve is self adjusting.

[This message has been edited by gregr75 (edited 03-14-2024).]

1985 Fiero GT MAR 14, 12:23 PM

quote
Originally posted by gregr75:

Ok I'll probably hookup the EGR solenoid hose the way Pontiac intended…

I'll chalk up the loud hissing noise to an IAC valve that was stuck open (retracted position) I can't find any other explanation it went away after I sprayed the whole throttle body area with carb cleaner.

However In playing with the valve and experimenting with it, the spring and pintle went flying out and I ruined it trying to put it back together.

I just received a new IAC valve, The pintle sticks out less than 1 1/4" The Pontiac service manual says "
No physical adjustment is made to the IAC
assembly after installation. IAC resetting occurs
after reinstallation on the vehicle, and is
controlled by ECM action when the vehicle is
operated."

So, why do some people perform a "reset procedure" by jumpering the ALDL. I guess I don't understand the purpose of it if the IAC valve is self adjusting.



The reset procedure is just a trouble shooting step, if you have a vacuum leak, and the ECM is trying to control idle, it is hard to find the leak, it is easy to "turn off" the ECM supplied air by extending/shutting the IAC valve, then disconnecting it. You also do that if the idle air screw was messed up, to reset the base, uncontrolled idle, so the ECM is happy later. The hissing sound was likely just some debris/oil/carbon in there, the PCV system can spit oil into the rubber snorkel if the PCV valve is jammed, causing other stuff in the intake to get clogged.