Questions and Answers

Mercury Tracer Stalls At Idle Q. Dear Vincent: I have a problem with a Mercury Tracer that is driving me crazy. I have spend many days trying to fix it, have taken the car to my mechanic, etc. The problem persists. I would really appreciate any help you can provide.

The car:
1994 Wagon
1.9 SOHC 8V four cylinder engine
Automatic transmission
190,000 miles
SEFI

It is in excellent shape and has been working great until recently. The problem started 2-3 weeks after I replaced the timing and accessory belts and accessory belt tensioner.

Problem description: Stalls at idle when warm. Turning on A/C help a lot - stalls much less frequently. If you keep it idling with A/C off - it will stall in a few minutes. Does not make a difference whether it is in Drive or Neutral.

Attempted troubleshooting:

• Checked for trouble codes. KOEO (Key On Engine Off) test show code 111 - no problem. Engine running test displays code 172 - "no O2 (HEGO) sensor switching, lean condition."
• Tried swapping in a known good O2 sensor. Did not help. O2 sensor was replaced recently.
• Checked spark plugs and their gap. Excellent condition, correct gap. They were replaced two months ago.
• Checked ignition cables. Resistance measured 1300-1500 Ohm. Checked insulation by submerging in water and measuring resistance. Tested fine.
• Checked EGR valve by substituting a gasket without air holes. The valve does not leak air at idle. Remounted the valve using a new gasket.
• Looked for damaged vacuum hoses. Replaced one cracked hose that runs from the valve cover to the bottom of air cleaner assembly. No change.
• Replaced three more cracked vacuum hoses: one that connects from under throttle body to vapor canister solenoid, another that connects the solenoid to the vapor canister and another that connects vapor canister solenoid to the fuel tank. No change.
• Checked the rest of hoses and found all in good condition. Tried to spray carburetor cleaner around all fittings, injectors, etc. to detect vacuum leaks. No effect on the engine.
• Tried switching gasoline brands. Tried using Chevron Techron Concentrate. Tried B-12 Chemtool fuel injector cleaner in metal can.
• Cleaned throttle body and Automatic Idle Control valve.
• Tried swapping Automatic Idle Control valve with a new one.
• Fuel pressure tested by mechanic.

Recent maintenance:
• Replaced timing belt, accessory belt and accessory belt tensioner.
• Changed oil and filter.
• Changed air and fuel filters.
• New O2 sensor.
• New spark plugs.
• New front brakes: pads, rotors and hardware.

Do you have any thought? Something I missed? It really sounds like a vacuum leak somewhere, although I cannot find it!!! Please help!

Vlad

A. It sure as hell sounds like a vacuum leak to me too. The O2 sensor being latched at full lean confirms a definite lean condition. In this case it is not the cause, but rather the effect, and a clue.

I would go back and check all the hoses again, including the PCV hose. A bad PCV hose would definitely cause this problem.

If you have 35 - 45 psi of fuel pressure at idle, you're good there.

I would check compression in the cylinders. While this is not an interference engine, the timing belt may have jumped a tooth or two. So that would be the next thing to check, the timing belt and tensioner installation.

If the condition persists, then you're going to have to take a look the fuel injectors and ECM.