My 1989 Coupe has recently developed a rough idle, surging at times. It will accelerate smoothly and does not create a Service Engine alert or any code.
I have checked for vacuum leaks, disconnected the EGR valve, replaced the fuel filter and the ECM. No Change. I pulled spark plug wires, one at a time, and the problem does not seem to be located at a single cylinder. It is more random and actually seems to cycle on and off.
I need advice from anyone that has experienced this type of C4 behavior.
Dan

 

The '89s came with multec fuel injectors from the factory....these things are problematic to say the least. You may want to ohm your fuel injectors to see if you can detect a shorted coil inside each injector. There is a "sticky" with a video for how to do this on the top of the C4 Tech/performance page.

 

Clean the IAC valve pintle shaft and passage way located on the passenger side of the throttle body.

 

Sorry, but this just bugs the $hit out of me. You can't "ohm" anything, you can instead check the resistance with an ohm meter. When you measure the voltage of something are you said to "volt" it? Didn't think so. Although most people know what you're talking about, people who know anything about electrical circuits will immediately draw conclusions about your knowledge when you misuse the terminology as such.

FWIW, most "telephone poles" don't have telephone on them!

I guess this is what happens when you grow up with an electrical engineer who works for the local utility.

 

Having a bad day, are we

 

My '85 has the same problem; it also stalls out when idling sometimes, too.

P.S. Took it to a shop and they said it wasn't popping any codes, and the catalytic converter needed to be replaced. That didn't fixed anything.

 

No, not at all. It's just that people ask for advice and people give it. Then the people who give it get upset that the people who asked for it don't listen to what they have to say. If you take a little time and use proper terminology, it will look a lot more like what you know what you're talking about.

 

It is just slang.....dang. You do make a very good point though. Your preaching to the choir on this one....I myself used to work for an electrical utility company as an electrical engineer and heard the whole telephone pole thing over and over -- but it never really bugged the $hit out of me. Down here most of the power poles do have telephone them and CAT TV too....those carriers just pay a small fee to be on the "power" pole......guess we should just call them all "utility" poles to add even more confusion to it.

The reason I use the term "ohm" is because most non electrically inclined people have a hard enough time figuring out how to use a(voltage/resitance/ohm) meter and telling them how to use the "resistance" setting to measure resistance is just silly and adds an extra step of confusion for them to struggle with. Telling them jargon/slang like "ohms" in a way helps them to put the test meter on the "ohm/s" or Ω setting so they can do what they need to do and move on.....much simpler I think....not technically correct but more simple.
FIC (Jon) I'm sure has heard the question "how do I hook up the meter and which setting do I use" quite a few times so I'm guessing this is why he made the video to show how to hook up and do the fuel injector resistance/ohm checking tests....I do not know the the OP electrical background so I simply referred him to the FIC "sticky" if he was confused.

Side note: I also call tissue paper "Kleenex"

 

The trouble with using slang to make it easier for people to understand is that they repeat that slang and it gets to the point where people try to use the slang in places where it shouldn't be. I've always thought it better to teach somebody. If you must "dumb it down" explain that you are dumbing it down and explain the right way too. If they choose to read it great, if not, that's their problem!

Me too. However, if I go to a restaurant and order a Coke and they bring me a Pepsi, I get upset. I didn't order a Pepsi, I didn't order a Soda, I ordered a COKE. The difference with the Kleenex is that if somebody gives you an off brand, it's probably gonna work just as well!

 

Well...........This was the first time I had used the Forum and it certainly has been entertaining! I appreciate each and every input and will be doing the "tests" as soon as possible. I promise to report back what I find and if there are others that want to contribute another approach to solving this problem, their input will be used also.
I am impressed with the responses, Thanks again.
DK

 

I've done it all, mine still idles rough. Finally just have gotten used to it.

 

I know these guys made it look like a s, it is not like that here they are just looking to help you and the rest of us the best they can
come back for more insanity tomorrow

 

Stick around, it gets better.

Your procedure sounds good. I think most would agree that vacuum leaks are the most common cause of bad idle. I wonder if you could have a vacuum leak in a system that cycles on and off, rather than having vacuum on it constantly. Does it idle poorly right from the get-go or does it deteriorate as the engine warms up?

 

On my 86, it had the surging idle and would idle rough. I had to change the intake gaskets, I also changed the injectors with the ones from fic. Most of the vacuum hoses and the coolant hoses while it was apart.
It now idles steady, but a little rough. That may just be the way the thing runs. I don't remember anyone on here talking about how smooth their car idles.

 

To All:
Thanks for the additional info. I had to travel this week-end and did not get to spend much time with the C-4. The idle is worse as it warms up. Initially, the rpm is higher and it seems to help, but as the engine warms and it drops the rpm, it becomes unsteady and then it will cycle between idling somewhat rough to surging if in gear. If out of gear, it does not surge, just idles rough. This car has 61K and used to be almost perfect. It was as smooth as one would expect a normal vehicle to be. Now, I knock it up into neutral as I approach a traffic light or intersection. I am just going to have to find more time to spend with it.
Thanks again,
Dan

 

Like one forum member said here, it idled well when it left the factory. Just keep at it, you'll get it sooner or later, hopefully sooner

Jim

 

Are your plug wires arcing? Raise the hood, start the engine at night or in a darkened section of your garage and pull the hood lamp fuse. Look for tell-tale electrical creepy crawlies along your ignition wires.

 

If you want to check for arcing, do what was said above but use a spray bottle to spray a fine mist of water around and you can see the arcing easier.

Also, how are the plugs? I changed distributor caps, plug wires and finally the plugs before it went away.

Also, get a scantool and check the IAC counts. Something you might do is take the IAC motor out and clean the entire TB. Remove the IAC housing to do this and then reset it.

 

Something you might do is take the IAC motor out and clean the entire TB. Remove the IAC housing to do this and then reset it. Reading Your above entries how do you clean and reset the IAC

 

I would take the TB off then take the top plate and the lower housing off. Spray all passages with brake cleaner and clean it with a soft brush. See if there is any carbon build up in the passages.

To reset the IAC, I would get the car warm and running then when it is in closed loop, let it idle. Get a scantool and check for IAC counts. Should be about 15-20 counts. Use the set screw to adjust it. When you get it done, reset the TPS to 0.54V. That is the process I use.