Hi Guys

this is my first post on a forum.

Have an issue with high idle on a 1999 prado that myself, mechanic and auto electician and also electronics technicians can not solve

The air flow meter, isc valve, and tps are all within spec.

Have all the correct voltages at ecu.

replaced sensor for coolant and has been tested as working correctly,

ISC and throttle body cleaned, isc tested open and shut on 12v.

The engine has been run on computer with nothing showing up, timing perfect.

Im suspecting the ecu as the cause.

The funny part is that if the coolant sensor is pulled while running, the engine runs perfect and idiling at 750 compared to its normal 1100.

Any ideas would be appreciated.

regards
jas

 

Thermostat stuck open not allowing engine to run at proper temperature?

Something with the coolant circuit or actual temp is wonky.

 

Hi mate

Thanks for the reply. I have only owned this vehicle a few weeks and i inherited it with the idle issue.

The heater was not working when i got it and flushed it out and works fine so im thinking at some stage some crud has been in their.

Also in the isc valve it was looking like it had been dry at some stage eg red dark marks on the isc pipe and chamber inside.

If the thermostat was stuck open, how would this impact on idle as heated coolant would still be able to flow past sensor at engine temperature.

I get plenty of pressure in top hose and heater works fine now

I have checked the coolant sensor at varying degrees and within spec

I can see where your coming from

cheers
jas

 

A stuck open t-stat does not allow the coolant temp to get to full temp so the ECM thinks it's cold and keeps the idle up.

 

I will test it tommorrow. But im fairly confident that the coolant temp sensor gets up to the required voltage to trigger the computer it is warm enough to reduce idle. But will double check.

It has had a new radiator put in at some stage so may of got hot and fatigued the thermostat.


cheers
jas

 

Take a look at this thread.

Yes, replacing the thermostat with a new one fixed the high idle for this member.

 

Are you able to read the coolant temp data live??

Just what live data did the computer confirm??

It should show a bad sensor or open thermostat

Then that system could be quite different then what we work on.

It has to be on our engines a high idle if all else is correct would trip the MIL

 

Sounds like a very similar problem. The fact it has had a new radiator and possibly over heated is pointing that way.

It wont hurt to flush the whole system out and replace coolant and thermostat and gasket. Ill give it a whirl in a few hours

thanks again

jas

 

Thanks for replying wyoming

All i know is the mechanic read the temperature sensor temp and it was reading 67 degrees or 152 f and he felt the radiator hose and said that was working about right. Im not sure how long the engine was running for at that stage.

You dont know off hand at what temperatue or resistance the system triggers to reduce idle and normal operation as all i have is a range of resistence at certain temperatures, but difficult to test without a scan tool

I know i tested the resistance at temp sensor at operating temperature running for about 20 min and it tested within the specs of the genuine workshop manual. Cant remember the figures off hand now but can check again

thanks for your help
jas

 

Normal operating range for coolant temp after warming up: 80-95c, 176-203f per FSM. Possibly, you may need to leave the rad cap off and use a stick thermometer in the rad to confirm the coolant temp as it heats up.

The temp you cite above is quite low.

 

Im trying to find the relevant info in the manual regards operating temperatures and cooling parameters i seem to be missing sections particularity servicing the coolant system... so forth

 

Try this link for a 99 3.4l.... I suspect the temp ranges are similar for your rig.

 

Just did my test on the temperature sensor switch before i pull out the thermostat

After running for 20 min and hot as it gets idling.

I got .8 volts

service manual says .2v-1v so it is at higher end but still within spec

the resistance was 200ohm

service manual states at 80 degrees c it should be between 200 and 400ohms

What do you guys think? Still suspect the thermostat?

 

T-stat is quick and and easy......install with jiggler valve down in the 6 o'clock position.

 

Pulled the housing off the thermostat and guess what someone had removed the guts of the thermostat and left just the surround in the housing

has me worried i know the radiator was replaced and i found a blockage in heating . The isc was originally looking dry.

Im wondering if they have really had some heating issues with the engine, i guess some blockages would do that......

has me thinking now

about to install thermostat back in fingers crossed

 

Well, well that would qualify as a permanently stuck open thermostat.
Get it back together and post up the results.

You might as well check the fan clutch while you are in there. Again, there are threads around here on how to do it.....sometimes using google search is the easiest and likely will pop up the threads from here.

 

Mate...

You were right on the money. I new as soon as i started it up she reved her head off to 1600 and has never done that, soon settled back down to 750 rpm right on the dot..

Worried what other demons they were trying to hide but so far so good, fan kicked in at start, but couldnt get it to engage but it is almost snowing on the mountains near here haha

Rang the mechanic i was so happy haha, i dont blame him it is hard to know where to look after you seemingly exhaust all options. We both would of never thought a thermostat could impact on idle so much.

Mate if your ever in Australia i got a beer, meal and accommodation for you..

thanks champ

regards
jas

p.s out of all this at least i can say i know how to troubleshoot electrical issues on the 5vz-fe because i looked at them all including schematics so forth and know that part inside and out. Now its time to have a play around and enjoy the car.

 

The 152 Degrees was a dead give away as to a bad thermostat or bad sensor.

Just curious why you and the mechanic did not pick that up??

In any case glad that this part is working

 

Hi Mate

Yeah very true im not a mechanic myself i just like to try and solve issues that come my way, like a good challenge.

Unfortunately i didnt have the operating temperatures( and not that familiar with correct operating temp) and coolant procedures. I had tested the voltages and resistance at the sensor and they were saying it was correct to the ecu.

I am still a bit confused about how a thermostat can make such a huge difference on a fuel injected engine with all these senses.

The mechanic tested on his scanner but i dont think he "tracked it" as such if thats possible as i have never used a scanner.

I did ring him and i had no idea where the temp needle in the car was suppose to sit, it was sitting low about a 1/4 where it should of been just under half apparently and he was like oh ok, but im sure he should of asked those questions, but then again he was not familiar with isc, tps and air assist so forth.

The trouble when you get a new car with no history or not knowing how it operates normally.



regards
jas

 

Jas,
Excellent news!! A legend might be stretching it a bit. Haha Your issue had a familiar ring to it.

Enjoy winter! I'm headed out for a 20k walk in the sunshine. Hopefully, my snow skis are out by mid-November.

I do know some cherry farmers outside Adelaide. Who knows, someday I may make it over that way.

We look forward to your contributions around here on the site.
Cheers!