2003 2.2 Cavalier Auto

When I clear the code, it comes up as P0300 Random misfire for 5 minutes, then it changes and stays as P0302 Misfire cylinder 2

I checked compression: 170/170/170/160
Fuel pressure on the rail is 160

I replaced:
Spark Plugs
Spark Plug Boots
Coil Packs
Ignition Module
Ecm
Fuel Injectors

The car drives great. It has a little bit of a rough idle. The exhaust does smell a little rich. Spark plugs look perfect. I pulled the new plugs out after driving a couple of days and they look perfect. I ran sea foam through the intake. Ran trans fluid through the oil. Nothing has changed.

I am coming up on my smog test and need to figure this out. Any help please.
I just ordered a fuel pressure regulator, and map sensor. After that I am completely out of ideas.

I also just ordered a IAC valve.

I read a article from another guy that had similar issue.

If I never let the car idle the code never comes up. If I start the car and drive, jump on expressway for 15 min.... no codes.

If I start the car and let it idle in the driveway for 5 min, the codes come up.

The car is idling at 500 rpm. I did notice if I put on the ac so a load is on the engine it seems to help. Takes much longer for the code to come back.

I am not 3rd savy but mechanically very savy..In my opinion you have done all the listed items that would contribute to your issue.Aside from say a restricted cat convertor or muffler this would be present in my opinion along with the engine temp rising,bad odor from cat or exhaust in general.In my thoughts with all the so called high tech tell me what is wrong we often can overlook something that can trick the ecm and engine to run stupid that is low cost to resolve.I while could be totally wrong in my thoughts/theory it could be your coolant temperature sensor is not reading (effectively) or 100% accurate and this can make the engine/ecm make the car run like crap based on certain conditions,and or actual car operation by a driver.I know this totally goes against the grain as your temp gauge or dummy gauge may never light up but,the engine temp affects how the car idle's and adjust to conditions.Just a mere idea outside of the NORM as I was educated lately with a similar issue with another car from a post with issue's and none point to yes the said engine temperature sender as failing or not working properly all the time and it was a 2.4.I learned this here on the jbo last week.At best just check your temp sender's connection and if it is the original I would try it as a fall back out the window idea.While I am 1st gen savy the temp sender make's a major difference in how the ecm/engine can run if weak or poor connection or just a short in the terminal to the sender making it run all stupid.My thoughts.

Funny you should say that. Just today I got a p0128 code. Coolant code.

Yes, this has been very frustrating. I am not a true mechanic. My dad is a mechanic of 40 years. I read it could be the timing chain, or valves sticking, and he says no. no. no. The car would be running much worse if that were the issue. And I ask what could it be.... and he shrugs his shoulders and says no idea.

I noticed today the coolant temp read 195 on the gauge both times I drove it... already warmed up.
I checked it with my scan tool and it verified the temp was close to what my gauge was reading.
I am going to check it 1st thing in the morning cold and take it for a 30 mile trip and see what is happening.

I have noticed if I run the ac it helps prevent the check engine light from coming on.

Are you thinking thermostat, or temperature sensor?

I will be subscribing to this, as I am in the same boat, well mine is cylinder 1. Also I just replaced the head with a rebuilt one, along with lifters, pushrods, water pump, timing chain and tensioner. After getting it all back together, I had a 0301 code, but only at idle, driving the car is great, so I checked compression first, 200/195/190/190 new spark plugs but I swapped with cylinder 3 just to be sure, stayed on 1 swapped wires with 2, stayed on 1, swapped coil packs, stayed on 1, last thing to check is fuel injectors, it seemed like 1 wasn't working as well, so I got new injectors, misfire stayed. I'm at a complete loss as to what's next. Also I had to replace the coolant temp sensor because the original broke, the replacement seems loose and disconnecting, I may just have to get another 1. Good luck, hope you find it, and I'll update if I do.


Josh

Carl I overlooked your last comment thermostat or sender.If it were thermostat it in my thoughts create one of two issue's.Either the car would run warmer than normal or even a lack of heat from the heater core when the heat was running.I would lean more towards the sending unit.Granted running the AC makes the fan cycle which inturns cools things to reduce heat.Granted the scan tool showed you the engine ECM reading that can be a False reading as it is showing what the ecm is getting from the sending unit.I would buy a thermal gun for low cost to verify the engine at idle at the normal reading on the gauge and then double check the tool designed to aim at the engine for a accurate engine temp.Scan tools are great but they show soley what the ecm is reading from each sending unit no matter what it is.I think the thermal temp tool is under $30.00 just check around.I will say this and be done temperature sending units can do all kinds of whacky things and not read a true temp due to age,wiring and or poor connection.If I come up with other ideas I will post it up.

after fighting a cylinder misfire code for my 2.4l for a couple months now I finally got rid of mine, it ended up being cheap autozone plug corks/wireset. I went to NAPA and bought what they had and they were of much greater quality than the autozone ones. not sure if the 2.2l has the same ignition set up with the stupid plug corks but if so it is something to check.

One thing everybody tends to overlook is- it may be a bad sensor throwing a false signal. Or even a problem with the ECM its self.

Jake


The Cavalier is the '55 Chevy of your generation.