rough idle
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
My 89 has the same thing too. The list of new parts on mine (to correct this problem) is much, much longer than your list. I believe this condition in "normal" for this year car. Oh yes, I bought a scan tool too 
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
I seem to remember mine running smooth before I killed the multecs with Seafoam. Now I have the same issue and are still throwing parts at it. I've got a friend with a scan tool and we are going to see what that yields. Whats funny on mine, one day it seems smooth and the next its kinda missing. 
Burning Brakes
Joined: Dec 2000
Posts: 1,161
Likes: 0
From: Orangeburg, NY
Check the throttle body for carbon deposits, including the IAC and ports. Clean the throttle body and make sure you use fuel injector cleaner and NOT carb cleaner.
The 89's came with multec injectors and have had issues. Many of them fail at 70k miles. It may be time to get them replace.
The 89's came with multec injectors and have had issues. Many of them fail at 70k miles. It may be time to get them replace.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 414
From: WV
This could be your problem, if you used injector cleaner this can kill stock Multecs in days. When I first bought my 89 it ran perfect, 2 days later after using injector cleaner it was missing badly. Come to find out the cleaner eats the epoxy around the injector coils and this shorts them out. Ohm your injectors hot and cold , they should all be around 16 ohms, if they aren't they need to be replaced. WW
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
Shorted Multec injectors will make the car idle rough and more important...run like crap. The first post indicated the car runs great except for the idle. I would be surprised to find he has shorted injectors.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 414
From: WV
Im no expert but my 89 ran pretty good except for the idle and I had three injectors that where reading low, something like 12 to 14 ohms each. Maybe he just thinks its running fine because at higher rpms a slight miss is harder to detect. It also makes a difference if you have one injector that is way off or a few that are each a little off, but you may be right. Only a ohm test will tell....
WW
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Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
WW: I do agree that the resistance of the injectors should be tested as this is an easy thing to complete. Perhaps floridatim will get "lucky" and this will be his problem. When the resistance of the Multecs get in the single digit range, the engine performance goes "south" quickly!
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I'd try to isolate a cylinder first - either read the exhaust temp at each - or take some 1/4 inch vacuum hose and cut it into 1/2 inch lengths. Then stick a piece between each plug wire and the distributor and with a grounded test light, touch the vacuum hose to kill the cylinder while monitoring a tach. Any that don't drop the same as the others needs to be looked at. And if it happens to be the #7 cylinder (especially since it's an '89), look for rust on the plug threads and run a compression/leakdown test.
Burning Brakes
Joined: Oct 2004
Posts: 898
Likes: 1
From: Pearland Texas
I'd try to isolate a cylinder first - either read the exhaust temp at each - or take some 1/4 inch vacuum hose and cut it into 1/2 inch lengths. Then stick a piece between each plug wire and the distributor and with a grounded test light, touch the vacuum hose to kill the cylinder while monitoring a tach. Any that don't drop the same as the others needs to be looked at. And if it happens to be the #7 cylinder (especially since it's an '89), look for rust on the plug threads and run a compression/leakdown test.
