Can a bad or faulty computer throw faulty codes?

[oblivion]

It could be, but these computers are extremely reliable and I would suspect the computer last. As mentioned, they usually will fail self-diagnostics and throw codes related to computer failure. For yours, I think you may genuinely have a misfire on that cylinder. You say the car runs really rough at idle sometimes... Gee, that sounds like one of the symptoms of a cylinder misfiring! So why do you suspect the computer?

In addition to the ignition components mentioned, you can also have a failing fuel injector or a valve train problem that could cause this.

 

[johnd]

I had the same code (on cyl #3of my car) and I checked everything that you did but still had the miss. Finally traced it to a missing platinum puck on the #3 spark plug. Plug change fixed it to this day.

 

[Vikas]

OP says he changed lots of parts in the last six month trying to solve this problem.

How about a complete reset and start from scratch?

1) Replace the spark plug with the exact OEM
2) Swap the coils
3) Swap the injectors

If the code still persists on the same cylinder, then adjust the valve clearance.

If the code is still there, now start tracing fuel and electrical wires and connectors associated with that cylinder. If you have insulation worn out on either the injector or the coil wire, you could have these kind of problems.

You also mentioned that disconnecting the computer completely and reconnecting it fixes it for couple of days whereas just resetting the computer brings back the code almost immediately. This is significant and you may be on to something. There may be some capacitor on that computer which has a slow "leakage current" and in that case you might be right and will have to either find the bad part on the computer or replace it. But there are other things which are more likely than the bad computer such as worn out insulation on the wires and you should eliminate them before deciding to swap the computer.

- Vikas

 

[oblivion]

"You also mentioned that disconnecting the computer completely and reconnecting it fixes it for couple of days whereas just resetting the computer brings back the code almost immediately. This is significant and you may be on to something."

I think it's more likely that when you disconnect the computer completely it loses everything---fuel trim tables, history, etc. and has to build back up from scratch before it can determine that a problem exists.

 

[Trav]

Pick up a cheap noid light.when it throws the code again connect the noid to number 4 injector plug(advance auto under $25)and see if you get output from the ECM with the engine cranking or running.
If yes you can more or less assume that part of the ECM circuit is functional.

If no pulses then check the wiring to that injector with a VOM set on ohms from the injector plug to the ECM with the battery disconnected.
Your looking for continuity in the wire not voltage.
DO NOT mess around with a VOM on the ECM circuits with the battery connected unless you know exactly what your looking for.

 

[JMac101]

Thanks guys I made the repair. After changing everything, I checked the manifold gasket and it was leaking, replaced it and Im good to go. No light, no code, purring like a kitten.
Vikas- I want to apologize, I was having a bad weekend last week and when I saw your post I took it wrong and exploded. Im sorry for venting on you and I appreciate all of your time and advice.
To everyone else thank you as well.

 

[Vikas]

No problem! I am glad that finally simplest of solution solved your problem.

Surprisingly if this were a carbureted car with no computer, the first thing you would have been told to look for intake leaks using spraying carburetor cleaner around the engine and notice the change in idle.

Did the gasket start leaking on its own or was installed incorrectly?

- Vikas