Car Idles High and Short Shifts

[froggy81500]

Originally Posted By: BearZDefect
Does that Avalon have a throttle valve cable from the throttle body to the transmission? Hard to believe, but my friend's 99 Camry i4 does, but that is a different transmission. My i30 does not, and it was made in 1996.

If there is no TV cable then the transmission control must rely on the TPS for throttle position input, so one guess is that it is getting an incorrect reading of the throttle position and thus shifting early and softly.

Can you test the throttle position sensor? I imagine they can get erratic. Just guessing here.


that's a thought but not sure how that would interpret into the higher idle.

 

[swalve]

I think BearZ has it. The cable is messed up and pulling the throttle open, and/or the TPS is out of whack.

Or a wheel speed sensor is giving erratic data. Making the engine think the car is moving when it's not.

 

[parimento1]

The throttle cable is fine, has plenty of slack. The car DOES have a TV cable. The throttle position sensor may very well be out of whack and I will check it tomorrow and have the specs for the correct resistance. Do you think it could be a lazy vacuum switching valve raising the idle or even the Idle Air Control? Also, how come there was no change in the performance of the car after removing the coolant temperature sensor- I mean I could have driven the car like that and not known it was disconnected.

 

[parimento1]

I realized in my haste that I removed the wrong cable, that was not the engine coolant temp sensor, but something else. I will have to look at that again tomorrow, i really screwed that up, sorry for the confusion!

 

[parimento1]

SO I pulled the Coolant Temp Sensor plug, the CEL came on for PO115, so I now know I have the correct sensor. I will check it tomorrow when the car cools down, because now it is idling fine. I will let u know the results.

 

[eljefino]

Usually gauge senders are single conductor; they ground through the sender.

Computer sensors are 2 conductor, they feed a positive voltage then the computer reads the variably reduced value through the other pin. This'll help you find the correct connector on similarly shaped doodads.

I rented a corolla that shifted at 3500 RPM flooring the gas when cold, I assume an anti-abuse programming. Since it can shift differently it says the computer controls shifting. The TV cable if you have it might be for transmission line pressure.

I suspect you are intermittently reading cold. Even unplugging and replugging the sensor connector might have cleared it up scraping off some oxidation.

A good way to check for vacuum leaks is to idle the car then waft an unlit propane torch around the gaskets and vacuum hoses. You can also spray WD40 but it's messy. The idle will change, typically smoothing out, if you nail a leak-- usually cylinders closest to the leak are running lean and the fuel system can only correct to an average.

 

[parimento1]

Yes, that is a VERY good point about the 1-wire vs 2 wire. I suspected that, but wasnt 100% sure. So, just to update, I started up the car and it drove normally, the engine idle was high until it warmed up then went back to normal, no unnecessary short shifting either. The CEL did not come on and throw a code for coolant temp sensor, so I am not 100% if it is coming from that, but it seems like a good guess. As for the TV cable, yes, you are correct, the TV cable is used for line pressure/shift firmness only.

 

[froggy81500]

Originally Posted By: parimento1
Yes, that is a VERY good point about the 1-wire vs 2 wire. I suspected that, but wasnt 100% sure. So, just to update, I started up the car and it drove normally, the engine idle was high until it warmed up then went back to normal, no unnecessary short shifting either. The CEL did not come on and throw a code for coolant temp sensor, so I am not 100% if it is coming from that, but it seems like a good guess. As for the TV cable, yes, you are correct, the TV cable is used for line pressure/shift firmness only.


I should have mentioned the 1 wire vs 2 wire thing but forgot about the relevance of it. Perhaps when you unplugged it and replugged back in it got a good connection. Not uncommon for the wiring at the plug to also develop a bad spot, kinda like how headphone wires do when you have to move them just the right way to hear anything. I had a truck who's temp sensor was close to something else and the wiring harness for it had to make a sharp bend around it. over time it developed a bad spot in the wiring because of it. Make sure the harness isn't sharply bent, pulled taut or rubbing on anything.

 

[parimento1]

I also should mention that this problem usually occurred after using the A/C for some odd reason, AND continued to occur for a few days after before settling down. I think it is the coolant temp sensor and if it needs to be replaced it is only 30 bucks. It is very hard to test the coolant temp sensor because its resistance varies with temperature and a few degrees in temperature can make a VERY SIGNIFICANT drop or rise in resistance. Testing the sensor in water, with a thermometer while using a multi-meter to measure the resistance isn't my idea of fun hehe.

 

[lipadj46]

Do you have an ODBII scanner that reads live data (AZ rents them for free)? Drive it around and see the temp that the sensor is actually reading. Also look at the other live data to see if there are minor misfires going on or something else that may be happening but not major enough to kick on the CEL.

 

[eljefino]

For grins also get your battery/alternator tested in case a low idle voltage is kicking the idle up as some sort of failsafe.

 

[mechtech2]

Sensors can be out of range and not throw a code. When they are really, puked, yes.

 

[parimento1]

I took out the car today to work, ran the A/C let it cool down, started it and it ran fine, no problems. Also took it out now for a little while, all was good. Maybe it really was just a bad connection with the sensor...I HOPE SO! I'll keep u guys updated.

 

[BearZDefect]

Originally Posted By: froggy81500
...
that's a thought but not sure how that would interpret into the higher idle.
I hope you have already solved it. Others have given better advice than mine.

But to explain how a TPS could cause high idle, many engine controls of that era would open the idle air control valve when they detect the throttle open. With the IACV thus open your idle would easily be 1,500rpm.

I guess two reasons why they open it that way:

1. To give you a surge of power so the test drive is more impressive.

2. They keep the IACV open while you have the throttle open, and only close it some seconds after you close the throttle, and then cut fuel. This prevents the sudden deceleration you'd get if they simply closed the IACV and cut fuel as soon as you let off the throttle pedal.


Some designs had an additional sensor to detect the throttle fully closed. This was used as input for cutting fuel on deceleration. Maybe also for unlocking the TCC.


It is amazing to me the lengths some manufacturers are going to these days to prevent this sudden deceleration. First problem is they use very soft engine mounts to absorb vibration, but these soft mounts mean the engine flops back and forth a lot. So, with modern electronic throttles, they close the throttle gradually. Simple enough. But some automatic transmissions unlock the TCC if it was locked so the torque converter soaks up the transition, then softly lock the TCC again so they can cut fuel. Older ATs that unlocked would not lock again during decel since they were not so desperately chasing EPA MPG figures as they are today.

 

[eljefino]

^ True all that. Have a saturn where the TPS recalibrated its zero point every restart. High idle going crazy? Turn the car off and on again, perfect! Worth trying.

 

[parimento1]

took the car out AGAIN last nite for an extended drive...all was well. Now for the last problem I have with the car that I have been chasing intermittently for the last 3 years.

 

[parimento1]

So, the CEL came on today again with 2 codes, P1300 (the old code) and P0115 the Coolant Temp Sensor code. Car was idling high again, etc. So I decided to splurge, so I replaced all 3 ignition coils and the P1300 (ignitor circuit malfunction) code went away. Replaced the coolant temp sensor (was only 30 bucks) car returned to normal idle and no more code. I'll keep you guys posted.