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Tom, ASE Certified Technician
Category: Car
Satisfied Customers: 25954
Experience:  ASE Certified Master Technician
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Isuzu Trooper: Engine will start and run fine while sitting.

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Engine will start and run fine while sitting. When put in gear and driven it will start missing and running rough. Then you have to fool around with the timing to get the motor to idle right at a different setting. The timing seems to float off mark as the engine gets warm.
Has the ECU been checked?Also timing is dead on?
Customer: replied 4 years ago.

ECU reads it is functioning and gives a corresponding code.No diagnosis as to anything wrong. When installing the timing belt everything as alined TDC with the gear markings . The original timing marks had floated off as the bushing slipped between the harmonic ballancer and timing gear. It was re-marked and timed at this point.

OK theres a good chance timing is off once again have you checked this?Also what code is stored in the ECM?
Customer: replied 4 years ago.

12. The problem is when timed the motor runs fine while sitting.. When driven it runs rough and the timing is thrown off. The timing point seems to float.

Yes that would be due to a problem with the tensioner or the cam or crank itself was this checked if not these need to be checked next.
Customer: replied 4 years ago.

If the crank or cam was bad the motor would never run smooth. Even while sitting.

Not until its put under a load in drive thats when this happens and timing jumps correct?
Customer: replied 4 years ago.

Not necessarily. A bad cam or crank would cause the motor to run rough immediately when the motor is started. I have delt with this condition in the past. Thanks for your input, I need to get another opinion.

Ok Im telling you from what i have seen is the cam is walking causing this issue .Over 20 years experience seen both cam and cranks have excessive end play and cause this issue .Best of luck to you .