Rough idle in closed loop, 89 Vette
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 892
Likes: 1
From: New Smyrna Beach Florida
Rough idle in closed loop, 89 Vette
When cold, it runs great. When it gets up to normal operating temp, it seems to "skip". I've heard other people having this problem, and hope someone has the solution. I've put in new plugs and wires with same results. Thanks for any help. Jimbo 89 
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 892
Likes: 1
From: New Smyrna Beach Florida
Let me tell you that it only has this problem at low rpm. It has good pickup, and runs fine with just a little gas, but the minute you get below about 1200 rpm, that is when it misses.
Burning Brakes
Joined: Aug 2006
Posts: 1,061
Likes: 99
From: Seattle WA
the symptoms you describe point to one or more failing injectors (common on '89+ with rochester/multech injectors). happened to me and new injectors solved the problem.
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
Another thing to try:
With the engine warm, unplug the EST (spark timing) wire, then start the engine and see if that improves the idle. If the car idles better with the EST disconnected, you could have a timing issue. If you have checked your timing and it is set correctly, take a closer look at your harmonic balancer. It may have begun slipping.
With the engine warm, unplug the EST (spark timing) wire, then start the engine and see if that improves the idle. If the car idles better with the EST disconnected, you could have a timing issue. If you have checked your timing and it is set correctly, take a closer look at your harmonic balancer. It may have begun slipping.
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Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Failing injectors could be the culpret...ohm them out...while they are hot and cold....and do the fuel pressure tests.ICM might be a good place to look too......remove it, have it tested, replace it if necessary, clean up the contacts on the connectors and put some vasoline on the connector points and use a heat disapation compound on the backside and pop it back in there.
Thread Starter
Burning Brakes
Joined: Jun 2008
Posts: 892
Likes: 1
From: New Smyrna Beach Florida
Sounds like injectors could be the culprit. Also sounds like they need to be changed anyway just because of their age. Thanks for all the imput will let you know what happens. Jimbo 89 
Instructor
Joined: Jun 2008
Posts: 138
Likes: 0
From: Bridgewater Ma.
I ohmed my injectors. (original multecs) Cold they were within spec. Hot, the readings increased abit on several.
IMHO these injectors are ticking time bombs and I will be replacing mine shortly.
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
If the car has the original multec's, that is your problem. My '89 Formula 350 had the same problem around 35K and replacing the injectors fixed it.
Also. check the ignition module in the distributor. Put new dialectric grease undeneath and reinstall.
Also. check the ignition module in the distributor. Put new dialectric grease undeneath and reinstall.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
You don't use dielectric grease. You use heat sink paste. It's in your FSM.
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
Same on the L98 too ace. It's in that FSM too.
http://forums.corvetteforum.com/show....php?t=2026663
http://forums.corvetteforum.com/show....php?t=2026663
