cleaned IAC..........still rough idle
Thread Starter
Intermediate
Joined: Oct 2003
Posts: 42
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From: San Lorenzo Ca
cleaned IAC..........still rough idle
Well I have been fighting an idle problem for 6-9 months now. Removed IAC, it was very very dirty(gunked up), cleaned that and the port, re-installed, set the TPS to .55 and the thing has not improved at all...........HELP
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: cleaned IAC..........still rough idle (89blkvet)
Did you also clean the TB plates & bore with some TB (not carb) cleaner?
Is the idle hunting or just rough? Hunting is often a sign of IAC problems; roughness could be from other sources, like injectors or ignition.
Is the idle hunting or just rough? Hunting is often a sign of IAC problems; roughness could be from other sources, like injectors or ignition.
Thread Starter
Intermediate
Joined: Oct 2003
Posts: 42
Likes: 0
From: San Lorenzo Ca
Re: cleaned IAC..........still rough idle (65Z01)
I cleaned as much as I could without removing the TB. And yeah..TB cleaner, not carb. The idle both rough and often hunting. It's perfect when the car is cold at first start up. Nice and smooth. Once warmed up, it dives very low and ruff........I screwed in the idle screw to try and maintain a decent idle, but you can tell she is ruff...........
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: cleaned IAC..........still rough idle (89blkvet)
Though you may not be getting any EGR code, check the EGR Valve to see if it holds vacuum.
I had a similar problem with the LB9 IROC which truned out to be a leaking EGR Valve diaphram.
I had a similar problem with the LB9 IROC which truned out to be a leaking EGR Valve diaphram.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: cleaned IAC..........still rough idle (89blkvet)
I have a Mr Goodwrench friend in OH who put a vacuum gauge onto the valve after it failed the e-check emissions test. Though the valve would move a little it would not hold vacuum.
There are some EGR test methods on my site using just simple tools. Maybe you could use engine vacuum at idle to test for a leaky valve(???).
To try it, hook a long piece of rubber vacuum hose between the FP port on the plenum and the EGR Valve port and start the engine. Once you see the EGR Valve open, pinch off the hose and see if the valve closes.
If the EGR Valve doesn't hold position when the vacuum line is pinched off you need to prelace the leaking the valve.
As mentioned, I've not tried this method but it is the only way that comes to mind without using a vacuum pump with a gauge.
There are some EGR test methods on my site using just simple tools. Maybe you could use engine vacuum at idle to test for a leaky valve(???).
To try it, hook a long piece of rubber vacuum hose between the FP port on the plenum and the EGR Valve port and start the engine. Once you see the EGR Valve open, pinch off the hose and see if the valve closes.
If the EGR Valve doesn't hold position when the vacuum line is pinched off you need to prelace the leaking the valve.
As mentioned, I've not tried this method but it is the only way that comes to mind without using a vacuum pump with a gauge.
Melting Slicks
Joined: Apr 2002
Posts: 2,118
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From: St. Charles, MO Route 66 Corvette Club
Re: cleaned IAC..........still rough idle (89blkvet)
Your 89 Vette (like mine) came stock with GM Multec injectors. These injectors have a problem in the coils inside the units shorting out and the injector does not function properly. It is easy to find this problem by simply checking the reisitance (better when hot) of each injector. The reading should be about 16 ohms for all 8 injectors. If you have a reading of 10 to 12, you have a bad injector! A bad injector will cause idle problems!
SAM
[Modified by Sam Lam, 6:44 PM 5/5/2004]
SAM
[Modified by Sam Lam, 6:44 PM 5/5/2004]
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Re: cleaned IAC..........still rough idle (Vett-eight-nine)
:cheers: Fluctuating MAF voltage due to power relay going bad caused my rough idle
:seeya
:steering:
Pro
Joined: Mar 1999
Posts: 678
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From: Oslo, Norway
Re: cleaned IAC..........still rough idle (89blkvet)
Hi.
I have had this problem also with the idle. I did a lot. Found that the EGR valve did not work as it did not hold vacuum. Cleaned the IAC and changed it also. .
The main thing for me was the vacuum leaks. Try some starting gas or propane and spray it over suspected areas as runner to the manifold and plenum. Check also the PCV valve. I had a big leak where the PCV valve rubberhose went in to the manifold.The rubber was bad
I have had this problem also with the idle. I did a lot. Found that the EGR valve did not work as it did not hold vacuum. Cleaned the IAC and changed it also. .
The main thing for me was the vacuum leaks. Try some starting gas or propane and spray it over suspected areas as runner to the manifold and plenum. Check also the PCV valve. I had a big leak where the PCV valve rubberhose went in to the manifold.The rubber was bad
Burning Brakes
Joined: Nov 2003
Posts: 935
Likes: 2
From: Beverly, NJ
Re: cleaned IAC..........still rough idle (jan-erik)
Try some starting gas or propane and spray it over suspected areas as runner to the manifold and plenum.
That does not sound very safe. :nonod:
Potential fire or explosion if it sprays on the wrong area, especially with a hot engine.
Be safe!!! :thumbs:
