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Disgruntled..... Emissions troubles

chevyaddict

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Jun 12, 2002
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894
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Tucson, AZ USA
Corvette
1990 Convertible
Hi all; Dawn here again. This weekend I am tackling this problem. Done some researching and it could potentially be the air control valve/diverter valve. THIS IS AN EXPENSIVE PUPPY! I was curious, how many of you out there had it to where replacing this solved your problems? Kind of makes sense that it might be the culprit considering I've replaced just about everything else and it is failing SO BAD at an idle and passing under load. Before I go purchasing this puppy - any last minute advice?;help
 

Top

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Joined
Mar 20, 2002
Messages
161
Location
Las Vegas, Nv
Corvette
1986 Convertible Dark Red Metallic
Dawn, Wait.....

What is the idle test limit on rpm in AZ? Here in Nev it is 1200 rpm. My car also fails at 550 but passes under load. I instructed the tech to 'high' idle the car during the test to the allowable limit. He ran it at 1150 rpm for the idle test and it passed no problem. I also had the car hot at 228 to kick the fan on.

Try running the test at the highest allowable idle speed. I'm betting you just might pass. If the tech won't hold the idle up that high with his foot on the gas, just set it high at home and lower when you get back.

Good Luck
 

chevyaddict

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Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
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1990 Convertible
Unfortunately they don't allow that in AZ. I tried that to get my 67 Camaro to pass and they would go for it. :( Thanks though! keep the suggestions comin' I miss driving it!!!
 

wishuwerehere82

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Sep 6, 2003
Messages
2,314
Location
Rochester, NY
Corvette
Red '82 Coupe,Sebring Silver '98 Coupe
chevyaddict said:
Nothing disabled on this car - no by-passing (I do that to the race cars... :); nor do I want to disable anything. Here are the readings:

HC Loaded 178 (standard is 220); idle 495
CO Loaded 1.08 (standard is 1.20); idle 3.91

It also idles slow (550) and the throttle position sensor occasionally overreacts (which I have replaced - didn't fix the problem) and makes it idle high while making the light come on. This is intermittent though...... Is there another switch or something or would it just behoove me to rebuild the TBI's?
Dawn,
Have you checked out your IAC (Idle Air Control) motors?
They regulate the amount of fuel/air mixture at idle, and can stick or fail after all these years. I have the same engine and "Mis-fire" injection on my '82 and have replaced both of the IAC motors on the throttle bodies.
It cured the jump in the acceleration, but replacing the MAP (Manifold Absolute Pressure) sensor on the firewall made a bigger diference in smoothing out the power curve. None of these are cheap, but it's worth trying, and are easy to replace.
Good luck!
 

Top

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Mar 20, 2002
Messages
161
Location
Las Vegas, Nv
Corvette
1986 Convertible Dark Red Metallic
From the AZ Code:

"Curb idle test. The test shall be performed with the vehicle in neutral for 1981 and newer vehicles. For 1980 and older vehicles, the test shall be performed in neutral, except that if the vehicle has an automatic transmission, drive shall be used. Engine RPM shall be within ± 100 RPM of the manufacturer's specified idle RPM."

550 is below normal so I would set the idle 100 over normal and see what happens.

Good Luck
 

Edmond

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Aug 1, 2001
Messages
5,218
Location
Louisiana
Corvette
2003 Z06
What about that little charcoal canister on the front driver side? Won't cracks in those hoses or the unit itself cause a poor idle and a failure in emissions?
 

chevyaddict

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Jun 12, 2002
Messages
894
Location
Tucson, AZ USA
Corvette
1990 Convertible
Edmond said:
What about that little charcoal canister on the front driver side? Won't cracks in those hoses or the unit itself cause a poor idle and a failure in emissions?
Replaced that a couple of years ago. Thanks though really.

Also, I already replaced the idle air controls because it was occasionally pushing out the code 22. However, even after replacing them it still does the same thing every once in a while. I do think intuitively that is where the problem lies but ????:confused Someone told me yesterday that if there is carbon built up on part of the throttle bodies it might be causing a mis-reading - but I didn't understand where he was stating exactly. Going to go tinker with it as soon as I am done with my Dually brakes.

By the way, TOP, that is really cool info! Where did you get it?

Thanks a million everyone!
Dawn
 
T

taegdh

Guest
My 2 cents.

As you have already run a high alcohol load through it, I was going on the idea that you had about just cleaning your throttle bodies and all the electronic attachemnts.

Last week someone else asked about passing emmisions, and I said then that I put half a tank of 93 octane in with a couple bottles of carb / FI cleaner, drive it for a few days, refill the gas tank and just put in one can of FI cleaner. That is the only times that I put FI cleaner in the car(s). Worked for me.

Check your gas cap. If it isn't tight something on the vacuum and fuel recovery system won't work properly, I can't remember the intracacies of it all but it does have to be on there tight.....

Lots of luck. Sounds like AZ is getting to be close to CA and the Northeast Tree Hugger States, for emissions.....
 

Edmond

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Messages
5,218
Location
Louisiana
Corvette
2003 Z06
taegdh said:
Check your gas cap. If it isn't tight something on the vacuum and fuel recovery system won't work properly, I can't remember the intracacies of it all but it does have to be on there tight.....


Good suggestion. I was going to suggest that but I just assumed that before they put your car on the roller thingy, they take off your gas cap and do the gas cap test.

When I worked on my old man's 98' Yukon, I replaced the EGR and the gas cap and it passes fine. Though with it being OBDII, I could get a specific readout that told me the malfunction. They didn't run the car, they just hooked up the diagnostic scanner and when it didn't flash any codes; they passed the vehicle for 2 years.

OBDI gets you close, but you still have to do a lot of the legwork. :(
 

chevyaddict

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Jun 12, 2002
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894
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Tucson, AZ USA
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1990 Convertible
She Passed!! She Passed!!

I finally had the courage to take her through yesterday and WOOO HOOOO! I suspect the IAT's had a lot to do with it but just in case I kept my foot on the throttle to raise the idle speed during testing. Passed with flying colors!

Thanks to everyone - wouldn't have made it without ya!:D
Dawn
 

WhalePirot

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May 9, 2002
Messages
2,942
Location
SoCA
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1984 White Z-51/ZF6-40/Shinoda body
maybe irrelevant, with your shiny new SMOG check, but...

What is the idle vacuum? Is it below about 18"? (Check that spec).

IF the vacuum is normal, and I believe that number is close, the MAP sensor may be providing a low number to the ECM, telling it the throttle is open more than it is, and the ECM adds fuel, as it does under acceleration. I'd test the sensor and the following first, though.

At 158k, the throttle body shafts are probably loose, from wear in the TB holes, being a rather soft metal. Years ago, I bought a kit, with a special drill bit and brass bushings to drill the shaft holes, then re-bush them. I have that bit somewhere, if you need it. This kit was not big dollars.

The TB gaskets may leak air, too.

To answer your other question, the TBs, however simple to teardown and rebuild, are a bit finicky to get exactly right. Having done this rebuild a few times with mixed results, I would have a pro do it next time then have them properly synchronized. BTW, I too, find Holleys simple, especially compared to Carter or Rochester carbs.

The AIR system initially injects air into the exhaust manifold, to assist combustion on a relatively rich exhaust. At the CAT and the engine warms, the SMOG pump air is then diverted into the CAT, for the same purpose. The idea in delaying air injection is to allow the CAT reach its operating temperature as quickly as possible. Under certain conditions, the air is diverted to a vent, reaching neither CAT or manifold. I'd have to pore through the manual to relearn when air is vented.
 

Top

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Mar 20, 2002
Messages
161
Location
Las Vegas, Nv
Corvette
1986 Convertible Dark Red Metallic
WOOOHOOOOO Dawn!!

Glad to hear it passed. :J
 

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