dglendon

99 Eddie Bauer Explorer 4.0 SOHC V6 150,000 km

Two problems started at the same time

1. temperature guage is running high then drops down hard after a while like thermostat was stuck and opened then heats up and down again, never really overheating but close

2. Truck starts up and runs perfect with ildle around 600 until temperature reaches 1/2 way mark then idle jumps to 1500 - 2000, temperature guage jumps up and drops down then up again (see problem 1)

After you let it cool down idle is perfect again until it reaches 1/2 way mark.

Where do I start to look, sensors, thermostat, throttle body?

In advance of any help - Thanks.

 

Indy Tech

First replace your thermostat may never have been changed in the past .
This could be your problem but you could also check the following .
1) Check Positive Crankcase Ventilation (PCV) System A high idle may indicate incorrect PCV valve size or a vacuum leak. Check PCV valve connections for leaks or cracks. Remove PCV valve and check for plugged or incorrect valve. Repair as necessary. If PCV valve is okay reinstall PCV valve and go to step 4)
(high idle concerns) or go to next step (all others).
2) Check IAC Solenoid Function Ensure all accessories are off. With engine operating at idle, disconnect IAC solenoid connector. If engine speed decreases or engine stalls, go to next step. If engine speed does not change, go to step 9) (high idle concern) or replace IAC solenoid (low idle concern). 3) Check For Plugged Throttle Body Plate Hole Remove resonator from throttle body assembly. Inspect throttle plate hole for restriction. Repair as necessary.
4) Check For Vacuum Leaks Start engine and allow to idle. Inspect inlet air system from MAF sensor to intake manifold for cracks, loose connections or faulty gaskets. Inspect intake manifold, EGR diaphragm and vacuum hoses for leaks. Repair as necessary. If no faults are found, go to next step. 10) Check Throttle Body Turn ignition off. Remove throttle body. With throttle fully closed, ensure light cannot be seen between throttle bore and plate. Snap throttle from wide open to closed position several times. Slowly cycle throttle from closed to wide open position. Check for freedom of travel especially during initial throttle opening. If faults are present, replace throttle body. If throttle body is okay, fault cannot be duplicated or identified at this time. Reinstall throttle body and check for additional symptoms and repair as necessary.

__________________
www.Flatratetech.com Staff Tech
Greg's Garage.

dglendon

Thanks for the suggestions. I have been too busy too look at my truck. I will be working on it tomorrow and let you know how it turns out.

baileymorales

I was having this issue as well and my father looked at my truck......turns out that the rubber seal on the air intake was rotting and stuck up inside the throttle body, causing it to sit. Take it apart and check your seal.

dglendon

Thanks for the advice guys. I replaced the thermostat and it cured the temperature variance problems. The idle also seemed to settle down but now I noticed the transmission started shifting hard - both upshifting and downshifting. The engine light also came on.

At this point I decided to take it to a transmission shop I trust and at least get the error codes read. Turns out the TPS was bad. It has since been replaced and I had complete fluid changes done on the transmission, differentials and transfercase. It runs better now than it has in a couple of years.

Once again thanks for the advice.