Oldsmobile Silhouette Misfire and TPS Codes

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2001 Oldsmobile Silhouette 3.4L Warning lights- Yes, Check engine light constant on Computer codes = cyl. 5 misfire, now has TPS code. Repairs made- NEW TPS, IAC, Crank Position Sensor, all 3 coil packs, spark plugs and wires, new fuel pump, professional on car Fuel injection cleaning.
Question = Misfiring at idle and driving, especially under load, but can occur at any time.

On hwy, van will hesitate /shudder / jerk; letting up on pedal and gently easing back onto it will correct the problem for a bit. Also stepping on pedal and shifting to lower gear seems to minimize at least feeling the shuddering. Especially noticeable cruise is on. Cruise and A/C on seem to make it worse. Within the last day have noted this: high idle, between 900-1100 rpm.

When driving at hwy speed with cruise on, kicking down pedal to pass will not cause downshift in transmission, and have watched the rpm DROP at this point from 2200 to 1500, van then slows down and constantly shudder and jerks. Turning off cruise and letting off gas for a second restores functionality. Also during these episodes, the check engine light goes from being on constantly to flashing. Most of the time it will return to a steady state, but sometimes will remain flashing until vehicle is restarted. This has been an ongoing problem for over 6 months, and would really like to get this solved, please help! Feel free to ask questions, I'll do my best to answer.

ANSWER:

The check engine light flashing is an indication that there is an engine misfire currently that is bad enough to cause possible catalytic converter damage. The way your Oldsmobile van is running would explain that, a misfire.

Normally a misfire under engine load as you describe is related to the ignition system. But since you have replaced the spark plugs, wires and ignition coils, this does not seem to be the case. The only other thing I can think of is that you have a bad fuel injector. Cleaning does not always help, especially if one has failed electrically. Doing what is called a fuel injector flow test would show a bad one. But this would not cause a high idle.

You could also have a plugged catalytic converter. A backpressure test on the exhaust would need to be done to test for that.

Another possibility is that you have an internal mechanical problem in the engine. One or more rocker arms may have come loose. We have seem many time the bolts that hold the rocker arm on loosen up and cause a misfire, especially if the intake manifold gaskets have been replaced with the last few months.