Why does my Infiniti J30 run badly or buck once it warms up?

Short answer: Two J30 owners had trouble once the engine was warm: one car wouldn't go past 3000 rpm with no check engine light, and another bucked going uphill. The owner of the first car told the second they were sure it was the crank angle sensor (in the distributor). Other members suggested checking fuel pressure under load and the oxygen sensors, and looking for cracked vacuum hoses.

Symptom: It starts and runs well cold. About 10 minutes later, warm, it won't pass 3000 rpm even with the pedal down. Or it bucks under load going uphill. The check engine light may stay off.

What to check first

1. Read the codes anyway. No light doesn't mean nothing is stored.
2. Have fuel pressure tested under load (one member said in Drive at about 2,000 rpm for two minutes).
3. Replace a dirty air filter and an old fuel filter.
4. Look for cracked vacuum hoses.
5. Ask a shop to check the crank angle sensor when it's warm and acting up.

Likely causes

1. Crank angle sensor failing when warm. A J30 owner with similar symptoms was sure this was the cause.
2. Low fuel pressure under load. Suggested for the bucking car.
3. Oxygen sensors. A mechanic tested them as fine on the bucking car.
4. Vacuum leak. The owner suspected a cracked vacuum hose.

What it usually costs

No owner posted prices.

Is it safe to keep driving?

A car that suddenly loses power is risky when merging or climbing hills. Avoid highways until it's fixed. Verify with a mechanic.

DIY or shop?

DIY for filters, vacuum checks and code reading. Fuel pressure testing and the crank angle sensor are often shop work.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists no recall for engine, stalling or drivability on the Infiniti J30 in the model years we could check on 2026-10-26 (the recall lookup returned an error for 2 model-year queries). Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: No recall we found matches this problem, so it's a normal repair, not a free recall fix. Still run your VIN, since other recalls may be open.
• NHTSA complaints: 20 keyword-matched complaints for Infiniti J30 1993–1997 (of 85 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-26; keywords: stall, buck, hesitation, surge, rough, jerk, power, sensor). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 93 Infiniti J30 after warming up the car runs horribly on Car Talk, a 1993 J30 ran great cold, but about 10 minutes later wouldn't pass 3000 rpm even with the pedal to the floor. There was no check engine light and no stored problem.
• In Bucking Infiniti J30 on Car Talk, a newly bought 1993 J30 bucked going uphill under load. A mechanic said the O2 sensors tested fine. Members suggested checking fuel pressure under load and the air filter. The owner of the first J30 replied that they were pretty sure the problem was the crank angle sensor, pointing to their own J30 thread about it.
• In Finicky 93 J30 on Car Talk, a J30 struggled when cold, and members suggested starting it with the pedal held down and checking the plugs and wires.

Quick tip

When a car runs fine cold and badly warm with no codes, think about parts that fail with heat. On a J30, that's the crank angle sensor.

Vehicle focus: 1993–1997 Infiniti J30 (3.0L V6).

Safety / mechanic note

Sudden power loss on a hill or highway can be dangerous. Verify with a mechanic.