Q.: mysterious idle oscillation when cold...'89 Jetta...

I'm back.

After a night or couple hours of sitting, my idle RPMs will oscillate from 800 to ~2000 RPM at startup. After roughly 3 minutes of stop-and-go traffic, the idle issue disappears.

The car is an '89 Jetta (i.e., Digifant II ECU)

My gut is telling me that it's one of the temperature sensors on the front side of the head.

Any suggestions? Check the switches for continuity or resistance? If so, what should the readings be?

TIA! Darryl.

Reply to
Darryl
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A bentley will help. :-) Check the switches on the throttle body and related wiring. Check the throttle plates for ease of movement, some become sticky with lack of lubrication and may stick partially open. Check ground wiring at cyl head coolant pipe or intake manifold (brake master side). Sometimes that wiring breaks.

later, dave Reminder........ Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you are a mile away from them, and you have their shoes. Frieda Norris

Reply to
dave

I have a Haynes. Throttle body has been cleaned up although when cold, I can hold it at ~3000 RPM for about 45 seconds and the problem goes away. That's why I'm thinking it's temperature related.

All good.

Reply to
Darryl

My oxygen sensor has been acting up, and it takes a few minutes for the car to warm up and clear its throat. I get hesitation, though, and not just idle speed oscillation. My front pipe (downpipe, whatever) is cracked, and I think the excess of oxygen at initial startup also contributes to the incorrect signal from the 02 sensor to the fuel controller. Runs rich at first.

I've had mechanics blame the idle fluctuation on the idle air stabilizer valve. The guy tapped it with a hammer and the idle speed fluctuated wildly. Those valves are expensive (around $200) and I've never found a used one, so I just live with it.

Theo

Reply to
Theo

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