hot weather = high rpms????

[ESnyder]

Anyone ever had any trouble with hot weather causing your truck to run at higher RPMs? My truck occasionally wants to idle over 1000, in park well over 2000. With AC off only slightly lower. It doesn't seem to do it in cooler weather. I don't drive it much, but it didn't have any trouble this winter or spring. Only showed up again yesterday, which was our first really hot day (around 90 or so). My truck is a 93 with 181K miles. Similar thing happened last summer, but I didn't think much of it, again because I don't drive it too much.

It does it after I've run it for a while. The truck isn't overheating, everything else seems to be OK. It was running fine, I parked it, came back, started it, and it started revving high. I can run it for all day around town in cooler weather and it won't do it.

Sounds strange to me that air temperature could change the idle speed, but I thought I'd throw it out there to see if anyone had seen it.

Is the mass air flow meter temperature sensitive? Could the O2 sensors change in hot weather?

Any ideas?

 

[FJ40Jim]

Not sure about the 1FZFE engine, but some manufacturer's ECUs have code in them to help prevent overheating. When the ECT or IAT is above a certain threshold, the ECU will command increased idle speed through the IACV. this is done to spin the waterpump & fan faster, and to pump more air through the cylinders.

Anyway, it could be the ECU trying to head off a perceived overheating problem.

 

[cary]

Not sure about the 1FZFE engine, but some manufacturer's ECUs have code in them to help prevent overheating. When the ECT or IAT is above a certain threshold, the ECU will command increased idle speed through the IACV. this is done to spin the waterpump & fan faster, and to pump more air through the cylinders.

Anyway, it could be the ECU trying to head off a perceived overheating problem.

My old Nissan Pathfinder did this one time, it was 112f out.

 

[RavenTai]

is this wil AC on or off?

check your throttle position sensor and adjust it heat may move things enough to through it out, without that throttle closed signal the ECU will not aptempt to control the idle air control valve,

I am not aware of any idle up to contol heat in the 1FZ

 

[ESnyder]

I wondered also if the TPS could have anything to do with it. I'll look into it.

It does it with AC both on and off. RPMS are just slightly higher with AC on.

Curious to hear if anyone else knows if that engine is set up to idle higher to counteract overheating.

Thanks for the thoughts so far...

 

[ESnyder]

Another idea I hadn't thought of before.

On my 95 Discovery, the idle air control valve gets dirty, and will screw with idle speeds. Could it be the same with this truck? Seems strange heat would affect it, on the Disco it wasn't temperature sensitive.

 

[CJF]

Your exact symptoms (too bad we didn't get a follow up...):

https://forum.ih8mud.com/showthread.php?t=92996

Suspect the throttle cable sticking or out of adjustment first, cuz it's the easiest to check/rectify.

Curtis

 

[smokethedog]

Its your throttle cable. Adjust and/or replace. I adjusted mine and it helped alot, but it needs to be replaced due to the sheathing being hosed up in a couple of places...

 

[sjcruiser]

Since your issue varies with temperature raises, check your metered air intake hose for cracks.

 

[Miescha]

Its your throttle cable. Adjust and/or replace. I adjusted mine and it helped alot, but it needs to be replaced due to the sheathing being hosed up in a couple of places...

I have been having the same problems with my FZJ80 for the past year. I had the TPS replaced and no change.

What makes you suggest the throttle cable? I'm not doubting, just curious. In my case, I'm not sure it is weather related, but I know pulling up on the "go pedal" doesn't make any difference.

Perhaps more importantly, this only happens in a non-drive gear. That is, when this is happening, it will stop if I move the 80 into any forward drive gear or reverse. It then re-appers when I put the 80 in neutral or park (without ever touching the thin pedal at any time - only the brake to allow shifting).

Any more thoughts?

ON EDIT: If anyone is wondering, I've checked the hand throttle also - not causing an issue (locked off).

 

[ESnyder]

I will check out the throttle cable and see. Pulling up on the pedal does not make a difference, so not sure if that is exactly it. I will try to manually adjust the throttle next time it does it. If that does it, I'll replace the throttle cable. Maybe when it's hot the cable sheath gets softer and gums it up somehow... I've used silicon on stuck throttle cables before to let them slide easier in their sheath.

My truck does it in all gears, it will idle in drive at over 1000, and in park over 2000. It is enough that I need to apply the brakes pretty hard to stop in traffic sometimes.

I will check air intake hoses for cracks, as well as air filter box, etc. Maybe something in the air intake is expanding in the heat and letting more air in? That would have to happen after the mass air flow meter, though, unless it is not functioning. Would more air necessarily make the idle increase?

 

[cruiserman]

Ditto on the throttle cable. It's sticking. Replace it.

 

[Miescha]

Looks like I'll be replacinga throttle cable. My only question, why does it only happen (on my 80) when I'm in park or neutral (not a drive gear)?

 

[elhombre]

If it is your throttle cable, the next time you have the problem get under the hood and pull on the throttle. Try rotating the linkage where the throttle cable attaches to the manifold.If it unsticks and the RPMs come down, there you go .

 

[cruiserman]

Don't need to get under the hood. Pull the pedal back with your foot.

 

[smokethedog]

Looks like I'll be replacinga throttle cable. My only question, why does it only happen (on my 80) when I'm in park or neutral (not a drive gear)?

Mine did the same thing. When in gear, if I let off the brake, it would "idle" at about 15-20MPH. That has to be hard on the brakes, because when you are stopping, it is like stopping with your foot still on the accelerator a little.

I had a 402 code as well as MAF meter code (I forget the number). I was in the middle of moving across the country and had no time to troubleshoot it, so I dropped it off at the dealership to get fixed. They told me the MAF meter was causing the high idle, and it needed to be replaced. They fixed the 402 code and replaced the MAF meter ($$$, I'm still pissed about that ).

A couple of days later on a really hot day, idle was way up again. I adjusted the throttle cable and that fixed it (took all of 5 minutes). Idles now around 600RPM's. I dont think there was anything wrong with my MAF meter.

Like I noted in my earlier post, I still need to replace the throttle cable as the sheath is worn off in a couple of places. I also need to adjust the accelerator cable so it the transmission will kick down will less throttle, but will wait to wrench on that when I replace the throttle cable.

I just drove it 1800 miles across the country with no more high idle or CEL, and no issues. It ran like a champ. The warning I got from a Nebraska State Trooper did move the speedogear correction from slee up on my list though. Had my cruise set at 78 in a 75, got pulled over and was told I was doing 85. He was a cool about it and just gave me a warning.

The throttle cable adjustment/replacement is probably your problem, at least it is the first thing I would try if I were you.
hth,
randall

 

[CJF]

Don't need to get under the hood. Pull the pedal back with your foot.

I disagree. Trying (at the pedal) to push the cable through the sheath would not be as effective/definitive as pulling it through (or even disconnecting it) at the throttle body.

Curtis

 

[Miescha]

Alright, I still don't understand why it would be the throttle cable when it only happens when in gear (the cable isn't moving when I shift as I'm not touching the accelerator so ....).

However, I tend not to doubt the group wisdom of this forum, so next time it happens, I'll pop the bonnet and go to work on the throttle cable. In fact, as I have another order of sunroof parts I need to place with cruiserdan, perhaps I'll check the pricing on the throttle cable and just add it in the mix. I'd really rather skip the MAF sensor though, as it sounds pricey.

Thanks for all the help - I'll report back with the results.

 

[CJF]

Alright, I still don't understand why it would be the throttle cable when it only happens when in gear (the cable isn't moving when I shift as I'm not touching the accelerator so ....).

In your earlier post you said it only happens when not in gear.

Curtis

 

[cruiserman]

I disagree. Trying (at the pedal) to push the cable through the sheath would not be as effective/definitive as pulling it through (or even disconnecting it) at the throttle body.

Curtis

Huh? The cable is under tension, so just pull on the pedal with your foot towards the driver.