2003 Chevy Malibu 3.1L giving P0300 code

First check for vacuum leaks. 2nd do a power balance test.
what brand of plugs and wires were used? I would use the correct
ac delco plugs and wires if not used. more in this link.

http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[quote=”blobula” post=113038]Yep, I used the AC Delco plugs and wires.[/quote]

Then the above is a good starting point. 🙂

I would take College Man’s advice to heart and pursue the possibility of a vacuum leak. It’s very easy to over-torque the aluminum plenums on the 3.1 and crack it at the corners. I’ve done it. In fact, I’ll send you a picture late tonight when I get back to my tablet. You need to get a spray bottle with water and spray around all the vacuum related lines from the pcv line to the purge solenoid line around the throttle body. Also, spray the tops of the injectors. You will likely need a piece of heater hose to enable spraying injectors 1 and 5 in the back, as they are hard to reach. It could be that one or more of the injector rings did not seal properly. Try to determine if there is a change/ drop in rpm’s when you spray these areas. Given the work you performed, the symptoms described etc., it sounds vacuum related to me as well. Best of luck

The pictures were not as vivid as I remember. Here is one showing the rear passenger side of the plenum (alternator area.) I could not even see the cracks until I hit these areas with brake cleaner following a smoke test. I was using a cheapo torque wrench that went bad on me. If you have cracked the plenum, a salvage yard is the best option for replacement. Keep us posted

Please don’t let me try your patience. Before I went that route, I’d perform a home smoke test. This really works if you can’t afford a professional one and can stand the cigar, 🙂 it still sounds like a vacuum issue given the fact it disappears at higher rpm’s to me.

I heartily agree with the Master Mechanic Barneyb. I’ve thought the same thing about p0300. That code is about as useless as the cottage cheese in the green jello mom made 🙂

We’re just commenting about life as in watching the dash vibrate while the computer sets a p0300 code.

Well, those cylinders are controlled by 2 separate coils. It’s unusual to have 2 fail simultaneously. I’d look further at the crank position sensor(s) and camshaft sensor. It you have spark, the ignition module is doing it’s job. Check your wiring thoroughly. Perhaps when you performed the other work a wire was compromised or connection not good and tight. Another thought, …if the wire going to the 7x crank sensor is too close to a spark plug wire or touching the exhaust, etc., it could be misfiring from interference. This wire on older 3.1’s was a twisted purple and yellow wire that connects to the 7x sensor on the engine block and the ignition module. Test the 24x crank sensor behind the balancer too.

http://troubleshootmyvehicle.com/gm/3.1L-3.4L/how-to-test-the-24x-crank-sensor-1