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Intermittent Idle Problem

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Vdaddy

Guest
Recently finished rebuilding my 93 LT1 and have found that I now have an intermittent idle problem. Sometimes the car will start right up and idle fine, other times it won't idle at all, but will run at low rpms if I keep my foot on the throttle. Sometimes if I turn it off and restart it it's fine, other times not. No correlation to cold or warm start, outside temperature, etc. that I can see.

Any ideas?

Thanks.
 

BigRed

Well-known member
Joined
May 23, 2001
Messages
948
Location
Edmonton
Corvette
1985 Bright Red Rocket
My ideas are

Opti Spark
Vaccum Leak
Pistion not firing (on and off) See Opti spark hehe
Codes in computer havent been laid in yet (how many time have you ran your car (turned on turned off))
 
V

Vdaddy

Guest
I've run the car for several hundred miles over the last 3 weeks or so. Would a vacuum leak come and go? Would the OBD I system report cylinders that misfire (I know OBD II does)?
 

BigRed

Well-known member
Joined
May 23, 2001
Messages
948
Location
Edmonton
Corvette
1985 Bright Red Rocket
Ok that clears the Computer Issue.

As for the Vac leak Ya! Could be a bent line with a small hole or really anything.

I get the car to idle rough then pop the hood and listen and play/search the Vac lines just to clear that possibiltiy.

Other than that (I dont know enough about them) but Ive heard "Mysterious" things about the Optispark. If you find the Vac lines in tact just have the car put on a scope they'll pbly find it out right away.

Also if you have a code Scanner see what it says mabe its something like your IAC working sometimes and sometimes not (Gunk in the chamber)
 
V

Vdaddy

Guest
Thanks, Big Red. I'll take a closer look for vacuum leaks.
 

Paul G

Well-known member
Joined
Aug 27, 2001
Messages
200
Location
Griffith, IN, USA
Corvette
96 CE LT4 Convertible
My step sons Pontiac was doing something similar. Turned out to be a bunch of crispy plug wires. Sometimes they would conduct just fine. Other times they would arc to the block and misfire like crazy. Poor idle and no power. Best way to check plug wires is on a dark night start the car and look at the wires in pitch blackness. Blip the throttle a little and watch. If you see a nice light show time for new wires.

Hope you find it.
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Did you follow the recommened procedure for setting the base on the idle/idle air motor? Did you remove the idle air motor and clean out the throttle body? If so, it may not be setting back down right, or it is sticking on some goopey stuff in there.

Take it out, clean it all out, flush the t/b with good cleaner. Don't drip cleaner all over your opti spark.

Go back and follow the standard procedure for setting base idle. You will be back in business in no time.
 

RLD92

Well-known member
Joined
Jan 5, 2002
Messages
75
Location
Eaton Rapids Mi.
Corvette
1992 White Coupe
My 92 did this I replaced the Iac motor(valve) in the throttle body and that fixed mine. you might try cleaning it mine was black from carbon. If you do replace it you have to reset it turn key on (do not start) for 5 secs off for ten secs and it is done. You will need a 1 1/4 in socket to remove. Hope this helps.
 
V

Vdaddy

Guest
Just to tie this off, if anybody is interested.

I removed the Idle Air Control motor/valve, sprayed the hole in the throttle body really good with carb cleaner and ran a brush through it a few times, cleaned off the pintle with carb cleaner (don't move the pintle), put it back together and it's now running fine.

Thanks "69MyWay" and everybody that helped.
 

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