Why does my Audi 100 blow white smoke and run rough at start?

Short answer: White smoke with a raw gas smell at startup on an Audi 100 usually means fuel is leaking into the engine while it sits, from an injector or fuel pressure regulator, or that a cylinder isn't firing. If you're adding coolant, consider a head gasket. Hesitation from a stop on CIS-injected cars often comes from intake air leaks.

Symptom: The car smokes white and runs rough right after starting, or hesitates for a second pulling away.

What to check first

1. Check whether you're losing coolant.
2. Have the codes read and test for a dead cylinder.
3. Have the fuel pressure and injectors checked for leak-down.
4. On CIS cars, inspect intake boots and vacuum hoses for cracks.

Likely causes

1. Engine flooding from a leaking injector or pressure regulator. If an injector or fuel pressure regulator leaks, extra fuel fills a cylinder while parked. You get white smoke and a gas smell at start.
2. Misfiring cylinder. A cylinder that isn't firing leaves raw gas in the exhaust.
3. Head gasket. White smoke can also be coolant burning. Check if you're adding coolant.
4. Intake vacuum leak on CIS fuel injection. Older Audis use CIS, a mechanical fuel injection that measures air. It doesn't tolerate air leaks and hesitates when taking off.

What it usually costs

Owners didn't post prices.

Is it safe to keep driving?

A raw fuel smell is a fire risk. Get it checked soon. Hesitation in traffic can be dangerous.

DIY or shop?

Vacuum hose and boot checks are DIY. Fuel system and head gasket work go to a shop.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists Audi recalls that touch fuel: 98V332000 (1993-1994 V6: a fuel injector internal seal can leak fuel into the engine bay) and 00V084000 (1993-1994: fuel feed line may be faulty). It also lists 93V006000 (1989-1991: transaxle differential oil can evaporate and wear the differential). If your car is part of a recall, the dealer fixes it for free. Check your VIN at nhtsa.gov/recalls.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 23 keyword-matched complaints for Audi 100 1989–1994 (of 81 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-29; keywords: smoke, start, acceleration, hesitat, oil, stall) (NHTSA returned no data for 24 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Audi 100s 1993. White smoke when starting on Car Talk, a 1993 Audi 100S 2.8 V6 blew white smoke and ran rough at start with a raw fuel smell, but cleared up once warm. Members said the gas smell means unburned fuel and pointed to flooding from a fuel pressure regulator or injector, a misfire, or a head gasket, and asked about coolant use. New plugs and wires didn't fix it.
• In 1991 Audi acceleration problem on Car Talk, a 1991 Audi 100 with 215,000 miles hesitated for about a second when accelerating from a stop most of the time. A member said this model uses CIS fuel injection and to make sure there are no intake vacuum leaks, since CIS doesn't tolerate them.

Quick tip

Raw gas smell plus smoke means don't just keep restarting it. Find the leak.

Vehicle focus: Audi 100, 100 CS and 100 Quattro, 1989-1994.

Safety / mechanic note

Fuel leaks are a safety item. Verify with a mechanic.