Bad Mileage no High Idle (cold idle)

[JKrei]

I think its time to get some help from the corolla experts. I have a 93 corolla 1.6L w/5 speed at 120,000 miles. Normally I get 33+/- mpg regardless of city or highway driving. This past winter my mileage has went into the toilet. I have been getting anywhere from 20-25 mpg. Within the last 3,000 miles, I have replaced air and fuel filters, plugs, wires, cap and rotor, O2 sensor, thermostat and seafoamed and cleaned throttle body with no improvements. Tires are proper psi and size and correctly aligned. I have checked all the brakes for dragging, none are. I know winter blend gas gives a little worse gas mileage but this is ridiculous. The motor also doesn't seem to have high idle when its cold, it usually idles around 700-800rpms. When the car is warm, the idling will go from 700 to 1000 to 1300 at various intervals. Idling is steady at these rpms, but fluctuates from one to another (While at one stoplight it will be 700, but a few lights later it will be 1000 or 1300). Overall the motor runs like a top, just have been getting crap mileage and the idling issue. Does anyone have any ideas on what I could do to fix this? Any help would be great.

[Bitter]

try replacing the coolant temp sensor and go from there.

[JKrei]

I will pick up a new coolant temp sensor today. Is there anything else that I may have looked over? With gas going up, I need to get my mileage back up to normal. Does anyone know the proper way to set the throttle position sensor? I have haynes and chiltons books, but they are a little vague for my tastes. Thanks for any help

[speedy25]

You are overlooking the idle control valve. They typically need cleaning to correct idle problems.

TPS problems are usually driveability and not mileage. Hook up your ohm meter to it and make sure it has a smooth "sweep" as the throttle is opened.

I also recommend leak down tests for ANYTHING that isnt working right. (Just like Bitter says a coolant sensor is the root of all problems! ) If you have leaky internal parts no amount of tuning will correct it.

-SP

[JKrei]

I removed and cleaned the idle control valve along with the throttle body with no noticeable improvements. I followed the Haynes manual to check it by jumping the TE1 and E1 points. The engine didn't idle up to ~2000rpms. It simply idled down to 750rpms from 1000. What would be the best way to check the idle control valve? I just replaced the coolant temperature sensor, but haven't noticed any changes yet. Will be putting 100 miles or so on tomorrow. Have to see what happens. On a side note, any others with manual trans. find it very stiff to shift it until it warms up? Once it warms up, it shifts great, only stiff when cold?

[Kiwi-Corolla]

Originally Posted by JKrei

What would be the best way to check the idle control valve??

A good way to test that the IACV connector is receiving power is to check that the middle terminal is receiving battery voltage with the ignition switched to 'ON'. You should also measure the resistance between the middle terminal and each outer terminal of the connector by using a digital multimeter. It should measure between 19.3 to 22.3 ohms

[JKrei]

I just got done pulling engine codes from the corolla via the TE1-E1 jumper thing. I got a code of 41 which indicates an open or short circuit of the throttle position sensor. Could a faulty TPS be causing the crap mileage and weird idle speeds? I am assuming that this means the TPS is in need of replacement. If replacement is needed, what is proper way of setting the TPS position?

[JKrei]

Does anybody have any ideas on this? I could really use the help.