[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
> We are the folks in California that e-mailed you a while back asking about > why our squareback has such a rough idle when started up in the morning; it > sounds as if there is not enough gas getting to the fuel injection. After > about 1-2 minutes everything seems to kick in and the car runs like a champ. When car "runs like a champ", what kind of gas mileage? > After our mechanic tuned it up, he told us that that the rough idle in the > morning was normal, but after listening and talking to other squareback > owners with FI, I believe him to either be incorrect or just not too willing Rough idle when cold can be caused by a misadjusted throttle valve switch (as happened to me a few years ago). Follow adjustment procedure in Bentley for your year. Good idea to just make sure it's adjusted right anyway, whether or not this is your problem. Or maybe your idle is just set too low?? Assuming manual transmission, if the idle is set to 850-900 rpm, you are OK. Idle should be about 50-100 (?) rpm higher for AT. If rough idle is accompanied by whitish smoke, you are probably running rich. Many possible causes for richness. A bad injector is a common fault. You can test their spray patterns to make sure they don't leak or aren't sticking open. Again, see Bentley for details. One of the temperature sensors can also be bad, but you can test them easily before running around trying to replace (I'll explain below..). > raised his kids in a squareback, we have good reason to believe his over the > phone diagnosis of the temperature sensor being the problem. This mechanic I'm sure he loves the car, but he is just guessing. Don't simply replace what may be a perfectly good part with an expensive replacement without narrowing down the problem. > As for whether we want a temp sensor cyl head or crankcase -- we really do > not know -- is there a difference. My husband is looking at the Bentley > Manual who refers to them as being the same. Is it figure 7-5 in the > Bentley Manual. We really need some help on this. Thanks. You're looking at the cylinder head temp sensor. The air temp sensor is illustrated in Figs 7-7 and 7-8 (Fuel System section). Totally different sensors. But if either is faulty, you could be running rich, which might explain a rough idle during warm-up. Here's how to test them in the car when engine at room temp (cold). Need an ohmmeter. Head Temp Sensor: Unplug the single wire from the main wiring harness. Measure resistance between the wire (going to the sensor) and ground. Should be not more than 2500 to 3000 ohm or so. If reading is way different (by maybe 1k or more), *then* replace. Otherwise, it's fine. Air Temp Sensor: Unplug the connector to expose the two prongs of the sensor. Measure resistance. Should be no more than about 300 ohm or so. Again, if the reading is way off (+/- 100 ohm or so), the sensor is probably bad. But keep in mind that these parts usually are NOT to blame. Pretty robust bits. -Mark Fuhriman '69 Fastback Orinda, CA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org