Audi S4 High Fuel Use Points to VANOS Solenoid Issue

Having dealt with similar issues on my 1998 Audi S6, I have some experience with VANOS solenoid problems. The symptoms you describe, check engine light, increased fuel consumption, and low power, match what I encountered. In my case, the variable timing system was malfunctioning due to a faulty VANOS solenoid. The repair involved replacing the solenoid valve and checking the electrical connections. Total cost was around 250 Euro for parts and labor. The workshop first performed diagnostic tests to confirm the VANOS failure. They found the camshaft solenoid valve was not receiving proper power supply. After replacement, fuel economy returned to normal and the power delivery improved significantly. To provide more specific guidance for your situation, could you share: Current mileage on your S4, Whether you have any diagnostic codes stored, If you notice any unusual engine sounds, When the symptoms first appeared, If the problem is constant or intermittent This information would help determine if your issue matches what I experienced and whether you might need similar repairs.

Thanks for the detailed response. My S4 currently has 172521 KM km and the last service was done 2 months ago. The check engine light started flashing right after that service. The problem is constant and getting worse, especially during cold starts. I got the codes read and it showed P1349, which points to the inlet camshaft timing control circuit. The engine makes a slight rattling noise at startup that wasnt there before, making me wonder if the timing chain might also be affected. The oil looks clean with no signs of sludge, so that shouldnt be contributing to the VANOS issues. Would replacing just the solenoid be enough in this case, or should I prepare for a bigger repair job?

Based on your mileage and the P1349 code, I am increasingly convinced we are dealing with similar VANOS issues, but your situation might be more complex than what I faced. That rattling noise you mention is concerning, as it was not present in my case. When I had my VANOS failure fixed, it was a straightforward solenoid replacement. However, the symptoms you describe, especially the rattling during cold starts, suggest the timing chain might also be involved. In my follow-up maintenance, I discovered that VANOS problems often coincide with timing chain wear at higher mileages. The clean oil is a positive sign, as oil sludge build-up can wreak havoc on the variable timing system. However, given the warning signs, I would recommend: 1. Replace the VANOS solenoid first 2. Have the timing chain and guides inspected while the system is apart 3. Check the entire variable timing mechanism for wear My initial repair was 250 Euro, but if timing chain replacement is needed, you should budget for 800-1200 Euro. The rattling noise during cold starts is typically a red flag for timing chain issues, and leaving it unaddressed could lead to more severe engine damage. Would strongly suggest having both systems checked thoroughly rather than just replacing the solenoid as I initially did.

Thanks for your thorough advice about the VANOS system problems. After hearing about your experience, I think I will go ahead and have both the solenoid and timing chain checked. The additional cost is worth avoiding potential engine damage. The rattling noise during cold starts has gotten more noticeable this week, so your point about the timing chain needing inspection makes sense. Will schedule an appointment to have the full variable timing system inspected, rather than just focusing on the inlet camshaft solenoid replacement. Just hoping the total repair stays closer to 800 Euro than 1200 Euro, but better to fix everything properly now. Really helpful to know about the connection between VANOS failure and timing chain wear at higher mileages. Will update the forum once I get the full diagnosis and repair completed.