High revs after first start of the day.

Hey guys, last few days when I start the car for the first time of the day, the car revs at like 1500 rpm, if I put it in drive and go for a short trip, it goes back to normal or if I shut the car off and then re-start it it idles normally, aswell. Could it be that when the battery was out of the car for awhile, the PCM lost some of its driveability setting in it's memory? Heres the article that talks about that...

http://www.aa1car.com/library/battery_disconnect_problems.htm

BMD wrote:

Hey guys, last few dyas when I start the car for the first time of the day, the car revs at like 1500 rpm, if I put it in drive and go for a short trip, it goes back to normal or if I shut the car off and then re-start it it idles normally, aswell. Could it be that when the battery was out of the car for awhile, the PCM lost some of its driveability setting in it's memory? Heres the article that talsk about that...

http://www.aa1car.com/library/battery_disconnect_problems.htm

I think you have a handicapped coolant temperature sensor, which is open-circuit when cold and telling the Riv's ECU that it is mad freezing outside. When it warms a little it closes circuit, probably an arc or some such, and behaves normally until it gets stone cold again.

I could be mistaken though.

Can you reach it with a multimeter and see what it reads, or use a scanner (like Car Code or the OTC Genesys) to read it? Thet way you'll see what the ECM sees. Alternatively you can directly read the sensor BUT someone else will have to tell you whether it's lowest or highest resistance is at low temperature.

If my guesses are right: Most likely it is highest resistance at lowest temp. So if it's open-circuit, it's telling the ECM it's cold out and the ECM then sets idle high until it gets other input. Then operations go back to what you're used to.

So yeah I am not there to check but my guess is you need to replace coolant temp sensor.

Other thoughts?

Albertj

Albertj,i think you are right,mine did the same thing,it was the c.t.s.After e.c.u. cycled a few times, it solved it's self.Went to closed mode, instead of open. Starts normal again.

Yeah - I'd replace it not ignore it. The coolant temp sensor helps the ECU set proper fuel mixture and ignition timing. They are less than $15 each from Rock Auto and odds are not much more than that from the local NAPA or other parts store.

Albertj

Yes, replace it.Sorry i forgot that, mine somehow fixed it"s self, before i got to it.strange i now!!!

flyineagle96 wrote:

Yes, replace it.Sorry i forgot that, mine somehow fixed it"s self, before i got to it.strange i now!!!

Not that strange. If the break in the sensor is close enough to arc it will "carbon track" and establish some conductivity.

you probably would get a gas mileage improvement from replacing that sensor anyway but I can't guarantee.

Albertj

Thanks very much for that info guys, it wasn't that expensive so I went ahead and got a new ECT sensor. How much coolant will run out when I remove the sensor? and just to be certain, the location is on the head just below the thermostat, correct?

EDIT: Problem solved, it was indeed the ECT sensor, which is infact located under the thermostat threaded into the head and its got three wires coming from the connector which is entirely covered by electrical protective tubing. I needed a 19mm wrench to take it out. A significant amount of coolant did come out once the sensor was removed. Make sure to use thread tape or pipe thread compound on the new one before it is inserted and re-connect the clip, took about ten minutes. Thanks again to Albert and James for their help!