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Discussion Starter #1
Hi! I have an old Mazda 3 2003. 1.6 fuel. It started jerking (back and forward), like it was cutting off fuel, on highway at about 4000 rpm. Oil was low. Since then oil + filter, fuel filter and spark plugs were replaced. If I don't release gas but keep it jerking at 4000 rpm, CEL with P0340 error comes up. It clears after a while. Driving below 4000 rpm solves the symptoms.

It doesn't happen always. I can drive all day, city / highway, different rpm without problems, then it will start jerking in the evening. Or it w stop when I go to mechanic (happened twice).

I connected to obd2 app and when it is jerking, it jerks/hiccups exactly at moment when vacuum gauge hits max (near 0). When it is not jerking, I can drive at full gas at vacuum value about 0 without problems. At idle vacuum is at about -12 value.

Vacuum hose was superficially checked. VVT solenoid was not tested (might be dirty?).

Any ideas?

Screenshot is not at time of fault. For demonstration of what I was checking out.



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Discussion Starter #4
The problem got worse after few days, hiccups occurring at lower rpm.

Actually the problem was fixed after insulating few wires around top of the engine block (below air filter & computer). It was a really troublesome thing to figure out (various dealers suggesting replacing timing chain, etc. That would cost more than a car and would not fix the problem) but luckily an easy fix thanks to a smart service guy.

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