P0305 it says cylinder five misfire. i have changed the plugs, still comes up, i have switched the ignition coils, still same code, the plug boots are good. i dont not know what to do. i checked the fuel pressure regulator for wetness in the vacume line nothing there. i can only think maybe it is an injector? i also switched the spark plugs around to see if it was a plug issue no luck there.

SOURCE: 99 olds alero 2.4

I'm sure you have installed a fuel pressure gauge and monitored the fuel pressure while the problem is occurring?Another diagnostic tool which is easy to do,is while the problem is occurring,unplug one sensor at a time beginning with the Mass Air Flow first,.if it uses one.Many times,not always,depending on the sensor,if the sensor is taken out of the picture as far as what the PCM is seeing,like unplugging the MAF,the PCM will substitute the missing sensor output with a generic value that will allow the engine to at least run,and if unplugging for example the MAF,the engine idle speed returns to normal,you know you're onto the problem.You didn't mention if the engine ran ok other than the idle problem.As far as checking for vacuum leaks,i use something like brake cleaner or WD 40,more of a liquid,and it does sound like a vacuum leak.Plastic intake manifolds do develop nearly invisible cracks that open up more with heat.Revsisit the possibility.And as for the PCM,it is possible,but more likely a mechanical problem.Lastly,remove an O2 sensor or two before the catalytic convertor,run the engine and see if anything changes.Cheap way to verify the catalytic convertor is flowing and not restricting engine airflow,as i have seen bad cats cause misfire codes and strange problems.Good luck.

SOURCE: intermittant p0302,p0305 codes misfires

1990 olds cutlass ciera misfire

SOURCE: codes are reading cylinder misfire and replaced

does the check engine light come on b 4 or after

SOURCE: p0304 cylinder 4 misfire

2001 oldsmobile silhouette van misfire on cylinder 4

SOURCE: 1991 Olds Cutlass Ciera 3.3 v6 would start, run a

jrtvett's "unplug one injector and start" troubleshooting procedure would work if one injector is bad. If more than one injector is bad, then not so sure.
Like you mentioned, one or more injector(s) can go bad and it causes the others to stop working as well. After our experience, I am convinced this observation (fault mode) is correct (see below). Its as if upon warmup the solenoid in the faulty injector shorts, resulting in short circuit of signals to all the other injectors.
We have a 1989 Olds Cutlass Ciera with the 2.8L V6 that recently had the same fault: At least one injector went bad after warmup, then engine refused to restart. All other possibilities were eliminated, including crank shaft sensor, ECM, ignition pack, idle start valve, bad gas, rail pressure, etc.
No Service Engine light illuminated, and there were no fault codes in the ECM computer.
The jrtvett procedure could not easily be utilized in our case because all the injector connectors are underneath the intake manifold and inaccessible.
My cousin is a Ford mechanic told me of an analysis procedure Ford uses to troubleshoot injector problems. They display rail pressure on a LCD or CRT monitor and can see pressure drop with each injector's opening. Unfortunately, if the car is not starting, then this test will not be of much use. The engine has to be idling or at least all of the solenoids in all of the injectors operational to use this test. If engine won't start, then its clear none of the injectors are opening as described above, then no fluctuations in rail pressure would be displayed.
The shop that was working on our car decided to replaced all of the injectors, and the engine now runs like new.
Due to inaccessibility of injectors and fact these injectors were inexpensive ($40-$50 each), it was wise just to replace all six. Grading old injectors is not exact science.