Rough Idle
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Welcome
Ok your new to the Forum. Get your profile filled out, car year and name +.
When asking a question you need to state what year you car is to get an qualified answer. Different years have different ignition, fuel system and electronics and depending on what you have will affect the answers for you.
You will not get a lot of feedback if people do not know what you have. C4s vary a great deal from 84 - 96.
Ok your new to the Forum. Get your profile filled out, car year and name +.
When asking a question you need to state what year you car is to get an qualified answer. Different years have different ignition, fuel system and electronics and depending on what you have will affect the answers for you.
You will not get a lot of feedback if people do not know what you have. C4s vary a great deal from 84 - 96.
Last edited by pcolt94; Jun 16, 2013 at 08:02 PM.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Rough idle is almost always a vacuum leak.
They can be very subtle and the vacuum setup changed quite a bit over the various years so as pcolt94 said, you really need to put the year and other pertinent information into your post.
They can be very subtle and the vacuum setup changed quite a bit over the various years so as pcolt94 said, you really need to put the year and other pertinent information into your post.
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
I've noticed my idle quality too (1995 LT1 6-speed), when fully warmed it shakes a little and spins 950rpm, not sure if this should be a concern since it runs great otherwise. Generally it's a little hard to believe that a high-compression pushrod V8 should idle "smooooooth like buttah" as some other CF users claim. Shouldn't there be at least a little rumble or lope? I still plan to check the intake manifold bolts, as well as theck the EGR, PCV, TPS, IAC, etc.
Burning Brakes
Joined: Jul 2012
Posts: 897
Likes: 91
From: Poughkeepsie, NY
I've noticed my idle quality too (1995 LT1 6-speed), when fully warmed it shakes a little and spins 950rpm, not sure if this should be a concern since it runs great otherwise. Generally it's a little hard to believe that a high-compression pushrod V8 should idle "smooooooth like buttah" as some other CF users claim. Shouldn't there be at least a little rumble or lope? I still plan to check the intake manifold bolts, as well as theck the EGR, PCV, TPS, IAC, etc.
So yes they can run that well.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
See if you can isolate it to a cylinder by pulling plug wires or fuel injector connectors and looking for no difference in running. Make sure all plug wires are on plugs all the way down. Check for any sparking in the dark from the wires.
Make sure the EGR is closed all the way and that it moves freely. You may find something doing the basics before going off into left field and complicated areas.
Make sure the EGR is closed all the way and that it moves freely. You may find something doing the basics before going off into left field and complicated areas.
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Thread Starter
Heel & Toe
Joined: Apr 2013
Posts: 17
Likes: 0
Thanks for Help
Thanks for all the ideas. So far a bottle of Techron has helped. My mechanic says run the thing, it's almost 20 years old and only has 80K it must have sat a lot.
I'm going to install new plugs as well.
I'm going to install new plugs as well.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Yes.
It's for opti-spark. It has a normal distributor cap. But has an optical section that sends 2 sets of pulses for timing (to PCM) for the entire fuel and spark system. If the low resolution section develops a problem, engine might not run due to no injector pulses and no drive to coil (via ICM) to develop the spark.
It's a system that works great when it works properly with very accurate timing thru the RPM range. Unfortunately it lives under the water pump and is susceptible to failure if too much water (pump failure) pores on it. Keep it dry and don’t wash front of engine with a hose.
It's for opti-spark. It has a normal distributor cap. But has an optical section that sends 2 sets of pulses for timing (to PCM) for the entire fuel and spark system. If the low resolution section develops a problem, engine might not run due to no injector pulses and no drive to coil (via ICM) to develop the spark.
It's a system that works great when it works properly with very accurate timing thru the RPM range. Unfortunately it lives under the water pump and is susceptible to failure if too much water (pump failure) pores on it. Keep it dry and don’t wash front of engine with a hose.
Intermediate
Joined: Jul 2011
Posts: 42
Likes: 2
Try to de-carbon the combustion chambers; my '87 also idled rough after a lot of slow driving. I had it done professionally but you can do it yourself-they make a product sprayed
into the throttle body called Sea Foam. It works. In the old days you would just steam it
by trickling some water down the carb while revving it a bit. Anyway it worked for me.
BonAir
into the throttle body called Sea Foam. It works. In the old days you would just steam it
by trickling some water down the carb while revving it a bit. Anyway it worked for me.
BonAir