Good evening everyone,

The engine turns right over and runs after 18 months of inactivity due to cradle, suspension, brake and fuel line replacement, etc.

However, it goes right to about 2200 RPM and there is a very loud hissing noise sounding coming from underneath the air cleaner.

I have everything hooked back up as far as I can see. (The engine did have to come out of the car during restoration.) There are 2 metal air tubes that run together but are unconnected but I believe these go nowhere by design after a recall, correct? The smaller tube terminates underneath the air cleaner on one end (its blocked or clogged at that end- deliberately?) and runs across the front of the engine bay is open at the right end. The larger tube about the width of a finger is about 2 feet long and is open at either end.

Not sure why the hissing noise but it is loud, This photo was taken underneath the car looking up at the two tubes I'm talking about.




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87 GT Stock 2.8L

[This message has been edited by gregr75 (edited 03-08-2024).]

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

Patrick is correct on the vacuum leak. You will need to check all vacuum lines. Check also for cracked plastic vacuum lines, or simply disconnected lines.
If a loud or noticeable hissing sound and high idle, is signs of a vacuum leak.
Also check the EGR tube.
There is 2 vacuum lines under the TB. Check there too.
The other spot that I have already seen a huge hissing noise, I forgot to connect the tube from the valve cover on the bulkhead / firewall side to the TB air filter to TB rubber tube.
Behind like this picture, the tube could be just disconnected.
Have a look.
Check to while your at it, the 2 TB to air filter tube clamps. But this won’t affect the idle speed.
It’s just check for proper seal on the intake tube.
Just a flat screwdriver is required to check tightening.



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fierogt28

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

[This message has been edited by fierogt28 (edited 03-08-2024).]

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

quote gregr75: There are 2 metal air tubes that run together but are unconnected but I believe these go nowhere by design after a recall, correct?

Incorrect
*The larger metal pipe was ‘removed’ from the engine {See Recall Thread Above} CHECK if you have the 1st Design or the 2nd Design in the link
*The smaller tube STILL must be connected on both ends {Outside Air to EGR Solenoid Vacuum}

quote The smaller tube terminates underneath the air cleaner on one end (its blocked or clogged at that end- deliberately?) and runs across the front of the engine bay is open at the right end.

Incorrect {Outside Air to EGR Solenoid Vacuum}
The smaller tube is connected to Outside Air (before the air filter housing input) and the “open end” goes to the EGR Solenoid Vacuum which feeds two ports: the EGR Valve and to the Throttle Body.


NOTICE on the Larger Metal Pipe w/ 'Open' Ends:
1st Design: the metal pipe was disconnected from the intake/vacuum system and replaced with a different (recall) Air Intake Duct
2nd Design: If both ends of this pipe is 'open' - CHECK the Air Cleaner Housing Side Port has been Sealed (capped off)

quote However, it goes right to about 2200 RPM and there is a very loud hissing noise sounding coming from underneath the air cleaner.

If you hear a vacuum leak underneath the air cleaner; check the air intake/vacuum system for 'open' ports (like the Air Cleaner Housing Side Port) which will draw unfiltered air to the system.

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

OK thank you everyone for your replies, wow this was a wealth of information, And I appreciate the effort that went into marking up some of these pics.

It looks like I have a second gen regarding the pcv redesign. However, the smaller metal tube thats supposed to connect to egr solenoid on the right side isnt connected, theres just a foot long length of hose dangling from solenoid. I could easily connect the tube and hose there but I have heard of other people just letting that solenoid hose dangle there because it's just ambient air right? This shouldn't affect EGR operation?

On the left side, where the small metal tube goes into air cleaner (see pic) The tube is blocked with something hard. Previous owner did a crude EGR delete, and I'm wondering if he deliberately blocked this tube.

I also performed the IAC reset procedure via ALDL for 20 seconds. heard some strange buzzing noises which didn't sound normal. I then cleaned the throttlebody and IAC porthole before the butterfly valve. Lastly, I install the air filter and cap and snorkel put everything together, fired up the engine and I now have 1000 RPM but very lumpy and almost stalling. Absolutely no idea why the loud hissing is gone, but I am very pleased with this and no more high idle.

I removed the IAC valve, and did a reset procedure again, really out of curiousity to see how it works and the spring and pintle went flying out but I was able to locate both parts.

Sorry for the long post but my questions are

1) Do I need to unclog the metal tube where it enters the air cleaner on the left side (see pic)and hook the EGR solenoid hose on the right side? Will this really affect solenoid operation versus just having a foot long hose hang off the solenoid like it is right now? It seems it wouldn't really matter because it's ambient air.

2) I screwed in the pintle of the IAC valve as far as I could go, now the slots in the pintle are lining up with the plastic guides in the valve body. is this how i should reinstall it? fully screwed in?

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87 GT Stock 2.8L

quote Originally posted by gregr75: Do I need to unclog the metal tube where it enters the air cleaner on the left side (see pic)and hook the EGR solenoid hose on the right side? Will this really affect solenoid operation versus just having a foot long hose hang off the solenoid like it is right now? It seems it wouldn't really matter because it's ambient air.

It probably makes little difference, do whatever you feel comfortable with. Do it like Pontiac intended, or have the hose just hanging off the end of the EGR solenoid. Your choice.

quote Originally posted by gregr75: On the left side, where the small metal tube goes into air cleaner (see pic) The tube is blocked with something hard. Previous owner did a crude EGR delete, and I'm wondering if he deliberately blocked this tube.

As I stated in the 2nd response in this thread, if the larger tube is open at both ends, make sure the hole in the air filter canister is plugged. The larger tube originally connected to the filtered side, whereas the smaller tube connects to the unfiltered side. The smaller tube being plugged at the air filter assembly makes no sense whatsoever.

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