Why is my Pontiac Fiero sluggish and running rich, or why does the idle surge?

Short answer: On the Fiero, start by reading the blink codes. Jumping two terminals on the diagnostic plug makes the check engine light flash them. One V6 owner whose car was sluggish and blew black smoke found the oxygen sensor had broken off, and a new sensor fixed it. If the idle surges up to 2,000 rpm or more while driving, clean the throttle plate and the idle air control passage first.

Symptom: The car is sluggish right after starting and barely passes inspection for unburned fuel (high HC). Or, while driving, it suddenly surges forward, and with the clutch in the idle sits between 1,300 and 2,600 rpm before slowly coming down.

What to check first

1. Read the blink codes by jumping the two terminals on the diagnostic plug as described in a repair manual.
2. Inspect the oxygen sensor and its wire. A broken or dead sensor makes the engine run rich.
3. Use fresh fuel if the car sits a lot.
4. Clean the throttle plate (both sides) and the idle air control passage if the idle surges.
5. Check vacuum hoses and the EGR system for leaks.

Likely causes

1. Bad or broken oxygen sensor. The fix on a member's 2.8 V6 Fiero that was sluggish and blew black smoke.
2. Dirty throttle plate or idle air control passage. The suggestion for the 1985 car's surging high idle.
3. Old fuel. Suggested for the weekend-only 1988 car.
4. Leaking or dirty fuel injectors. The 1988 owner's mechanic named the injectors as a possible cause of high HC.
5. Vacuum leak or EGR problem. The 1985 car had an EGR code, though blocking the EGR vacuum didn't change the surge.

What it usually costs

No owner posted prices in these threads. An oxygen sensor and throttle body cleaner are inexpensive. Injector service costs more.

Is it safe to keep driving?

A surging idle that pushes the car forward is dangerous in traffic and parking lots. Be ready with the brake and fix it soon. Running rich can also overheat the catalytic converter. Verify with a mechanic.

DIY or shop?

DIY-friendly. Blink codes, an O2 sensor and throttle body cleaning are home jobs. Injector testing is easier at a shop.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists these recalls touching this area of the Pontiac Fiero: 87V181000 (1984-1984 model years, engine and engine cooling); 89V232000 (1984-1988 model years, engine and engine cooling); 90V104000 (1985-1988 model years, engine and engine cooling). Check your VIN at nhtsa.gov/recalls. If your car is part of this recall, the dealer fixes it for free.
• Plain words: Recalls 87V181000, 89V232000 and 90V104000 covered Fiero engine compartment fire risks from connecting rod failures, oil, coolant and fuel leaks. They're not an idle fix, but any Fiero that smells of oil or fuel, or has leaks, should be checked. If your car is part of a recall, the dealer fixes it for free. Verify with a mechanic.
• NHTSA complaints: 4 keyword-matched complaints for Pontiac Fiero 1984–1988 (of 106 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-27; keywords: stall, dies, no start, cut out, idle, rich, high idle, surge, sluggish, hesitation, O2, emission). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 88 Fiero V6 sluggish when after starting on Car Talk, a 26,000-mile weekend car barely passed inspection for unburned fuel and was sluggish after starting. A member said to check the oxygen sensor and read the blink codes by jumping two terminals on the diagnostic plug. His own Fiero V6 had been sluggish with black smoke, and he found the sensor broken off; a new one fixed it. Another suggested old gas.
• In 1985 Pontiac Fiero "high idle" problem on Car Talk, a manual Fiero would suddenly surge while driving, and with the clutch in it idled between 1,300 and 2,600 rpm before slowly dropping. It had EGR and vehicle speed sensor codes, but blocking the EGR vacuum didn't help. A member suggested cleaning both sides of the throttle plate and the idle air control opening.

Quick tip

Read the blink codes first. It costs nothing on a Fiero and can point you right at a $40 sensor.

Vehicle focus: 1984–1988 Pontiac Fiero, 2.5L four and 2.8L V6.

Safety / mechanic note

With a surging idle, keep your foot on the brake whenever the car is in gear, and don't clean the throttle with the engine running. Verify with a mechanic.