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Faulty Idle Regulator

I recently bought a 1999 VW Lupo (essentially a two door Golf) with 30000 miles on it. My mechanic suspects it sat idle for a long time. Recently the check engine light went on, warning of a faulty idle regulator. What effect would you expect to see as a result ? Thanks.

Abnormally high idle while stopped at a light, or a tendancy to stall out while stopped at lights.

Thank you. As it happens there’s no problem with stalling . The major complaint is poor acceleration, even for a 1.4 liter engine and less than expected gas mileage, about 25mpg city and 45 highway.

Based on those symptoms, I would be more likely to suspect poor maintenance or perhaps a bad Mass Air Flow (MAF) sensor. When was the last time that the spark plugs and plug wires were changed? What about the air filter and fuel filter?

I just changed the air filter I used STP (the silver bottle) to clear the gas filter, which is located in the tank. The result of both was noticeable. I’ll change the plugs and wires next

One more thing. My mechanic says half synthetic oil will work better than all-synthetic for my old engine True?

Could you post the actual code here? Otherwise we are working in the dark. It should be a P0505, P0506, or P0507 if it a a code for idle speed control.

If you think 25 city and 45 highway are bad you must live someplace with a bigger gallon than the U.S.

Thanks Oldtimer. Where I live, in Sweden, gallons are the same but the price tag certainly isn’t. Last I checked gas here sells for US$9.43/US gallon. I’ll take every mile per gallon I can get