2001 Prism high idle

I have a 2001 Prism; 22,500 miles. This car was purchased this summer off a 92 year old who finally got her keys taken away. Thank God! The idle seemed like it might have been a tad high in the summer but now that winter is in full swing, it definitely is high. When the car is started in the A.M. the idle is high and it doesn’t drop, even when the gas pedal is “punched”. It sounds like it tries to fall to a more normal rate for a couple of seconds but it goes right back to its high state. No dash lights are on. I am going through gas quicker. I typically can get 100 miles out of a 1/4 tank of gas, now I get about 80. I drive 38 miles one way to work (x2 for round trip) on a turnpike with the cruise set at 65; very little city driving

Service center said it would be $60 to hook it up to a machine to have it checked. Is it worth the $60 or should I just turn up the radio? I don’t have a tachometer to see what is really happening.

Just a quick thought. Does the Check Engine (CEL) light come on for a quick second when you first start the car? All the lights on the dash are supposed to as a self-test.

A $60 diagnostic fee is really on the low end of the price scale. Autozone will check codes for free, but if the $60 is the minimum fee to diagnose the problem rather than just download codes, do it.

You do want to get this corrected. You’re probably running rich, and that’s not good. In addition to wasting gas you may cause premature catalytic converter demise.

Causes could a bad O2 sensor (low likelyhood as that would trip a CEL light) or possibly a bad temp sensor. Temp sensor would be my guess. A bad signal would tell the computer that the engine is still cold. Not only would it continually run rich, but it would not throw a code.

There are a few other possibilities, but I th9ink you get the idea.

What kind of machine are they talking about? What were they going to measure?

You need to have the possible error codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

BTW Measuring mileage by using the gas gauge is very inaccurate. However I am interested in the indicated drop in mileage. How long have YOU had this car? Was that drop in mileage with this car from the time you got it until now, or was it based you the mileage you were getting with a different car?

You really need to find out what the RPMs really are. It should not cost $60.00 for that.

The problem might be with a defective coolant temp sensor for the computer.

This is one of the primary inputs to the engine management system when the engine is first started. And because of this, this sensor will not always set a code. However, a scanner can monitor the coolant temp sensor signal both when the engine is started cold and as the engine comes up to full operating temperature. If this sensor is out of calibration, the computer thinks the coolant temp is still cold. This results in poor fuel economy, and the idle stays high because the computer thinks the coolant is still cold.


I went to AutoZone yesterday and no code showed up. They suggested I take it to the dealer. Joseph-I know it is not an accurate reading to use the gas gauge but is a form of self-entertainment to see if I can (visually) get more out of each fill up. When I did keep track of the mileage/gallons ratio I was getting 37 mpg. This week I got 28 mpg. No changes in driving-same driving pattern. I have been using the heater a lot more but I don’t have a car starter, meaning I am not letting the car sit in the driveway running for long periods of time. BustedKnuckles-the light does come on for a second or two on start up, so it is not burned out. I think I will bite the bullet and take it to the dealer after Christmas.

Seven years old, and only 22,000 miles …not many miles for things to start going wrong; but, they have, of course. Take notes for the (independent) mechanic: Does the engine cooling fan run (listen for it) while the engine is warming up? It shouldn’t. Does the engine temperature gauge, on the dash, reach at least 1/2 way after driving about one mile? It should. Leave your notes on the seat, for the mechanic to see.