Timing belt issue roughly idle up and down?

1991 MAZDA B2600

90,000 MILES • 2.6L • 4 CYL • 2WD • MANUAL

GABEJOHNSON22

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Hello, I recently did a head gasket change and now I feel like I have timing issues. The car will start but sort of roughly idle up and down until it settles at about 600-700rpm. Then sometimes right as I tap the gas, the rpms drop before revving to normal. I thought maybe it was an air filter or spark plug issue. So I replaced both and when I pulled the old plugs they were matte black as if they were running rich. I'm not sure of the issue or if I did the timing correct. Thank you!

Apr 25, 2026 at 11:01 AM

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STRAILER

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Hello,

Yep the spark plugs are carbon fouled and must be cleaned or replaced would be better. This can happen when the catalytic converter is clogged. After replacing the spark plug if you can upload a short video of the engine trying to start I can see what the problem is so we can fix it. Also, double check the camshaft timing which can cause this issue as well. Here is what it should look like. This engine has balance shafts as well so make sure the timing is correct for those as well. Check out the images (below). Let us know how it goes

Images (Click to enlarge)

May 1, 2026 at 4:55 PM