idleing really high

[bronco5.8]

hi i am new to bronco zone and i have a quick question my bronco is acting wierd it is shifting odd and it is idleing relly high and it has not thrown a code i checked it is running fine.In park about 2500 and in gear probly 1300 or 1400 and it does not want to run under 35 mph and it will get up to 25 by its self if you just let off the brake and its getting really crappy mileage it is around 10 and i normaly gets 13-15 depending how hard you drive i am thinking the thorttle possion sensor because right now some times you have to gas it kinda hard 3/4 or harder and let off to get it to shift in to overdrive the other gears it seems to rev higher than normal but i drive 60 miles to work and i havent noticed them as mutch as tring to get it into overdrive any help would be greatly appeacated and this is my daily driver

1993 bronco 5.8 auto push button 4x4 265K

 

[Krafty]

welcome to the zone. Can you describe exactly what it is doing when it is "shifting odd"

Sounds like it could be a vacuum leak, now there are pretty easy ways to figure out where it is,

if you have no brake power/ assist then it in your booster line, if your heater/ air direction dial is misbehaving then it is most likely the vacuum canister ( stores vacuum required to maintain a/c and vent air direction)

third is the Fuel pressure regulator which uses engine vacuum to control the amount of fuel. Note that Low vacuum from any of these leak locations will cause your fuel pressure to spike.

lastly is the vacuum modulator on the transmission which controls shift points, if your trans has one and is shifting odd then suspect number one is usually a disconnected vacuum line going to the trans or at the modulator.

Good luck.

 

[BroncoJoe19]

I agree that it sounds like the TPS.

While Krafty is right that it could be a vacuum leak.

You may need to use a couple of straight pins as probes to back probe the TPS.

you should get between 0.5 and 1.0 volts at idle, and it should gradually and smoothly transition to just under 5.0 volts at wide open throttle.

Reference voltage from the PCM should be 5.0 volts all the time.

 

[bronco5.8]

I looked at the last of the old vacuum lines and the new ones i put on.The heat and air work like normal. witch control the transmission shifting? And brakes are fine if not it would more of a beast to stay at a stoplight.and one other question what does the sensor over the heater and air box do? I have done the valve cover gaskets and have forgotten to plug in in a long time ago just worndering what it does thanks guys I will buy more vacuum line Friday and a tps sensor

 

[BroncoJoe19]

The heat and air work like normal. witch control the transmission shifting?

neither control shifting

Your trans is controlled by the PCM but it gathers info from some sensors, such as the TPS and MAP

Could it be that you left your MAP sensor disconencted?

It's high on the firewall - passenger side.

 

[bronco5.8]

Finally got the tps put in and did the rest of the vacume lines and so far runs fine we will see Monday wen I go to work in tyler it will be the first big trip 65 miles each way I hope the mileage goes back to normal thanks guys for you're help