My 1989 C4 some times starts to run rough like its on 7 cylinders and will cut out whilst idling.
It does not do it all the time. I am thinking it maybe caused by the fuel filter ?????
Anyone else had this problem ?????

 

Dirty injectors, worn tune up parts, worn engine. Start with the basics including a fuel filter.

 

Sounds like a problem with your fuel injectors. When was the last time they were replaced/ cleaned

 

OK, just went thru this with my "94" C-4 LT-1, turned out the distributor cap was cracked, needed new plug wires, and complete tune-up. I bought this car from out of state dealer back in January, haven't driven it much because of the weather. I did notice, before I put it away, it was running ruff sometimes and fine other times. Got it in to a dealer/service, they put the computer on it and this is what they found. Question, why would an automobile engineer put the distributer cap in behind the water pump. Because they had to pull the water pump, replace gaskets, etc. the final bill was $2400. Ouch, but she runs without a hitch.

 

Check old o2 sensors

 

When was the last time you did plugs, wires, cap, rotor, fuel filter, and checked timing?? I'd go through all that before I'd do anything more costly or complicated.

 

Before spending a lot I would try a can of BG 44K Fuel Injection Cleaner as it frequently cleans the injectors enough to give the car a smoother idle. My Buick DD had a slight miss occasionally and I poured a can into the gas and now my idle is smooth as glass.
If you have an aversion to "anything that you pour in the fuel" then check/replace the injectors. I get "heat" for suggesting what some refer to as a "Snake Oil", I swear by the BG products as do tens of thousands of mechanics every day.

Verify that your Fuel Pressure is in the correct range by attaching a Fuel pressure gauge to the Schrader valve/Fitting on the passengers side fuel rail.
The idea of a new O2 sensor is a good one as that frequently has a major affect on how well the engine runs. Thankfully your L98 doesn't have the dreaded "Opti" Ignition as that is another can of worms.
A new distributor cap and rotor would never hurt nor would new spark plug wires. Since the car is fairly new to you start it up after dark and open the hood. If you get a Tesla Coil Light Show under the hood then you have solved the problem.
Checking the timing is always a good idea but not likely the cause of the issues you described.
Spark Plug wires are notorious for failing and either grounding out or just not getting the electrical charge to the spark plug. It might be worth pulling a spark plug or two to see what condition they are in.
I would think that a good cleaning and checking of your Idle Air Control valve might be in order if the engine cuts out. I like taking a can of carburetor cleaner and spraying down the throttle body to get rid of any deposits accumulating inside.
The fuel filter needs an occasional replacement. After all of this if the problem persists then you might measure the resistance of the Fuel injectors to see if they are acting up. The ethanol in today's gasoline is notorious for eating away the original injectors.
Vacuum hoses on these older Corvettes are frequently past their prime, one of the first things I did was replace as many as I could with a roll of vacuum hose material. This brought my cruise control back to life. Follow the hoses and verify that your EGR Vacuum solenoid is working properly. If the EGR Vacuum solenoid is not working then the entire EGR system gets plugged up with carbon and your emissions will go nuts. If the engine detonates or pings then the EGR is a good place to start. I run 87 and 89 octane through my 1988 C4 without any problems. When the EGR system is not working the engine runs hotter combustion chamber temperatures creating more NOX which caused my C4 to fail emissions inspection in Virginia. Use the vacuum hose chart under the hood if you find loose vacuum hoses.

You don't want to have a cylinder missing regularly as it can hurt the catalytic converter and/or possibly dilute your engine oil.

I am a big believer at starting with the simple stuff and working your way on up from there. I have seen to many people start by replacing the ECM which is at the other end of where I start looking.

Having a copy of the Factory Service Manual is a must have for any C4. A code reader or scanner helps if you have access to one, it is so nice to be able to watch the data as the engine runs because the problems become visible.
If you have questions We (here on the Corvette Forum) have the answers!

Best regards,
Chris