Random multiple misfire replaced upper and lower intake manifold gaskets?

FREDERICK HUME

MEMBER
2005 CHEVROLET IMPALA
3.4L
V6
2WD
AUTOMATIC
200,000 MILES

I replaced my upper and lower intake manifold gaskets, spark plugs and wires. While repairing the car the plastic nipple that vacuum travels through on my MAP sensor snapped off. It was a clean break so I glued it back on and vacuum does still travel through the MAP sensor, as far as I can tell. Only I now have a random misfire with no (MIL) check engine light illuminated until I drive the car and it starts flashing. Could the MAP sensor be my random misfire?

Tuesday, November 25th, 2025 AT 3:24 AM

3 Replies

KRAKENAUTO

MECHANIC
69 POSTS

It won't usually cause such, have you rechecked your repair to ensure you didn't booger an injector or wire up? Also what quality of plugs and wires did you use in the repair? If the parts are cheap aftermarket you can try testing it by replacing it with the old plugs and/or wires and see if the misfire goes away, if they were not too bad to start with.

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Tuesday, November 25th, 2025 AT 9:37 AM

FREDERICK HUME

MEMBER
2 POSTS

I bought the plugs and wires from Advanced auto. If the issue was a faulty plug or wire, wouldn't I get a code for a specific cylinder as opposed to a 'random' misfire?

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Tuesday, November 25th, 2025 AT 1:06 PM

KEN L

MASTER CERTIFIED MECHANIC
54,137 POSTS

I agree with KRAKENAUTO, Also this car uses a MAF sensor as well, I would change that out and I would make sure the MAP sensor is not leaking at all, any miss reading from either of these can cause a random misfire. This guide can help as well

https://www.2carpros.com/articles/automotive-engine-misfire-code-p0300-causes-and-solutions

Please go over this guide and get back to us.

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Tuesday, November 25th, 2025 AT 2:09 PM