Why does my Infiniti Q45 die when I stop or let off the gas?

Short answer: A Q45 that stalls when you let off the gas or come to a stop most often has a dirty or failing idle air control (IAC) valve. That valve on the throttle body lets in just enough air to keep the engine idling when your foot is off the pedal. Cleaning it and the throttle body often helps. If it stalls mainly when you brake hard, have the brake booster checked for a vacuum leak.

Symptom: It runs fine while you're on the gas, but at idle or at red lights the RPM sags, it runs rough and dies. Some cars drop below 500 rpm when stopping quickly, worse when cold.

What to check first

1. Watch the tachometer at idle and when you come off the gas. A sag below normal idle points to idle control.
2. Clean the throttle body and IAC passages with throttle body cleaner.
3. Test the brake booster: at idle, press the brake hard. If the engine stumbles or dies, the booster may be leaking vacuum.
4. Have codes read and check for vacuum leaks around hoses and the intake.
5. Check when it was last tuned up (plugs, air filter).

Likely causes

1. Dirty or failing idle air control valve. Members' first suggestion in both threads.
2. Leaking brake booster. A big vacuum leak when you press the brake can stall the engine.
3. Vacuum leaks. Cracked hoses let in unmeasured air.
4. Dirty throttle body. Carbon buildup reduces idle airflow.

What it usually costs

No owner in these threads posted a repair cost.

Is it safe to keep driving?

Stalling at stops is dangerous: you lose power steering and brake assist and can be stuck in an intersection. One owner shifted to Neutral at every stop to keep it running. Fix it soon. Verify with a mechanic.

DIY or shop?

DIY for throttle body and IAC cleaning and the brake booster test. Replacing the booster or chasing a hard-to-find vacuum leak may need a shop.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists no recall for stalling at idle on the Infiniti Q45 in the model years we could check on 2026-10-24 (the recall lookup returned an error for 5 model-year queries). Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Other recalls to check: NHTSA lists alternator recalls 99V129000 and 02V171000 for some 1997–1998 Q45s, where a damaged diode can lead to alternator failure and an electrical short. If your car is part of this recall, the dealer fixes it for free.
• NHTSA complaints: 17 keyword-matched complaints for Infiniti Q45 1990–2001 (of 187 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-24; keywords: stall, dies, shut off, won't start, no start, cuts out, idle). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Q45 dies when not on gas on Car Talk, a '95 Q45 sputtered and died after idling a few minutes and at red lights, and needed revving to restart. A member pointed to the idle air control valve on the throttle body and said cleaning it and the idle air passage can fix it.
• In Engine will die when I come to an abrupt stop on Car Talk, a '92 Q45 with 110,000 miles dropped below 500 rpm and sometimes died when stopping quickly, worse when cold. Members suggested the idle air control system and a test: press the brake hard at idle to see whether a leaking brake booster is stalling it.

Quick tip

Clean the IAC and throttle body first; it's cheap and often works. If it only happens with hard braking, check the booster.

Vehicle focus: 1990–2001 Infiniti Q45 with the V8.

Safety / mechanic note

Stalling removes power steering and brake assist. Verify with a mechanic.