High idle in P & N after driving (1600-2000 RPM's). Anybody have similar issue?

[S.CarolinaFZJ80]

I assumed that but was unsure since there are no ribs on that vacuum fitting to hold a hose on. Plus I looked everywhere I could, physically looking and feeling & found no open fittings or loose hoses.

Any ideas General?

 

[cruiserdan]

If you look at the intake from the RH fender-side there is a bib right behind the throttle body that is about 5 o'clock, pointing toward the front of the truck at about a 45 degree downward angle. There is a horse shoe-shaped hose that runs from that bib down to the "T".

 

[S.CarolinaFZJ80]

Just was fishing around out there again while waiting for a responce. I will go check in that spot. Be back shortly.

 

[S.CarolinaFZJ80]

CDan - I found what you were referring to, pictured below. However, that fitting had a hose attached to it (although not too clear in the picture). It was attached to the rear part of the "T" fitting in question.
Although that wasn't not it, you did lead me to the leak. Thank you. The front part of the "T" fitting attach to a small nub under the intake, forward, up and to the left of the "T" fitting.
I bought some hose from the store but due to the location I will have to remove the throttle body to get to it. Since I will have it off, I may aswell clean it & replace the valve cover gasket.

 

[cruiserdan]

No, that is not what I was talking about. The "nub" you subsequently found is my "bib". As I stated it's behind the throttle body on the intake plenum.

 

[Red Fox Ranch]

I am having a similar problem... and cannot figure it out. My 80 will only do this when it is hot out, or have been running the a/c, usually both, but can just be hot as well. It will rev up to 2300-2500 and it doesn't matter if it is in P or N, you can feel it at stop lights etc. in Drive trying to push the trans. It only does it in the Summer hot months, it did it last year... then ran perfect all winter, now back to it. I've got to solve it because it's driving me crazy and I know its hard on the trans when shifting back into D from P or N. I figured it was some sensor or ??? causing it because it is just way too random and intermittent to be a continual problem.

 

[CJF]

I am having a similar problem... and cannot figure it out. My 80 will only do this when it is hot out, or have been running the a/c, usually both, but can just be hot as well. It will rev up to 2300-2500 and it doesn't matter if it is in P or N, you can feel it at stop lights etc. in Drive trying to push the trans. It only does it in the Summer hot months, it did it last year... then ran perfect all winter, now back to it. I've got to solve it because it's driving me crazy and I know its hard on the trans when shifting back into D from P or N. I figured it was some sensor or ??? causing it because it is just way too random and intermittent to be a continual problem.

Next time it does it, put it in park, pop the hood, and manually manipulate the throttle (just behind the throttle body) and verify it is able to close completely.

Check the dashpot adjustment (as notthejeepnomo mentioned), throttle cable for sticking/adjustment; basically everything in that area that might keep the throttle plate from closing completely.

Do NOT assume that a simple "stick your foot under the pedal and pull up" test is sufficient to rule out throttle adjustment/cable isuues.

Curtis

 

[S.CarolinaFZJ80]

Cdan - I can see this is going to get confusing, if that wasn't it... where does the fitting in my secound picture attach to? These are the only two fitting that don't have a hose attached to them, that I found. This fitting was facing the passenger side at a 90 degree angle from the forward facing "T" fitting is was about six inches forward of & to the left of the fuel rail, under the intake plenum forward of the throttle body. So you are saying there is another fitting up underneath the intake? If so, that means I need to find two more fittings up in that rat's nest.

CJF - Nothing is binding with the throttle cable or pedal.

theMule - sounds like you are having the exact same problem. The last time I drove mine before this was 5 weeks ago. It was alot cooler then and I had no problem. Now that the outside temps are getting up there I see this problem. Must be a connection. Especially I didn't touch or remove anything it that area during my repairs.

Oh well, as I said before, I'll just have to take the throttle body off to get to it because unless you are an extremely small midget, child or Japanese, the chance of being able to get a hand in there is damn near impossible.

 

[notthejeepnomo]

did you try and and push the plunger i was speaking of in a little to see if it would slow the idle speed?

 

[Red Fox Ranch]

So what sensor or device kicks up the throttle when you engage the A/C? Could this be the problem? I was thinking it had to be a sensor going bad, why else does it only happen when its hot? Or when the A/C is on? I took a drive yesterday up over the mountains on a muddy road to Park City, it's been rainy and below norm temps here in Utah, about 68-72 degrees, not a problem, drove perfect the whole trip... but a couple weeks ago when it hit 90 degrees for the first time and I was running the A/C, it went crazy, even after you turn off the A/C. I feel it is an electrical / ECU / Sensor problem vs. a mechanical throttle cable or vacuum leak, but ???

 

[Red Fox Ranch]

The other thing mine does also very intermittently is the idle sometimes in park will drop all the way down to the 500 rpm mark or lower and just sit. You can try to rev it to make it come up, but won't until it decides to.

 

[S.CarolinaFZJ80]

nothejeepnomo - I haven't messed with it yet. I have ordered the valve cover & throttlebody gaskets and am going to tackle all of it at once. I'll just take everything off, fix my leak, clean the throttle body & intake, replace all the vacuum hoses (including the one or two missing ones) and button it up with new plugs and adjust everything per the FSM, while crossing my fingers!

theMule - It definetly only happens when it's hot out too. I haven't noticed the low idle but not to say it won't happen in the future or if I was at altitude like you.

 

[S.CarolinaFZJ80]

Well I replaced the vacuum line that was missing. I started her up and she idled nice. So I thought the problem was solved, drove it home, put it in Park & sure enough the RPM's surged to 2,000 RPM's with the AC on (1850 RPM's with AC off).

Any idea's folks? It obviously wasn't the vacuum leak.

 

[pmccumber]

1) Pull the EFI fuse for 15 minutes, the thing might have learned a bunch of bad habits. That'll clear 'em.
2) Check your connectors on the TPS and IAC. I had a bent pin last week causing bad idles.

 

[S.CarolinaFZJ80]

Thanks pmccumber - I will check the pins and pull the EFI fuse for 15 minutes. I did replace the TPS last fall but it has not thrown a code since the previous sensor failed.
However, my truck idle's fine when started up. It's only after driving it for a bit, when it's hot, that the it idle's at 2000 RPM's. Is your's doing the same thing?

 

[pmccumber]

No, mine is beautiful, now. But it had two weeks of bad idling after cleaning up the throttle body. But as soon as that plug was pulled and the bent pin was found (not by me I might add), it has been perfect since. And then we pulled the EFI fuse and BS-ed for a while, plugged it back in, and it has been great ever since.

 

[S.CarolinaFZJ80]

I pulled the EFI fuse and relay in the electrical box and drove 4 times today. The P & N idle is down to 1200-1400 RPM. Not as bad but I see how it acts tomorrow and Saturday (the next time I can drive it) to see if it gets lower.
I may have to do the idle adjustment mod using o-rings to correct this if the ECU doesn't relearn soon.

 

[S.CarolinaFZJ80]

Well I drove it to work today (about 10 miles at highway speeds) & when I put it in Park , sure enough, the RPM's went back up 2000 RPM. I am pretty sure this has something to do with heat as during short trips, i.e. 1 mile or so, it has not done it since I pulled the EFI fuse & Relay. Coolant temp was in the upper 190F - 200F range while intake air was up at 160F.

Is the ECU possibly sensing these higher temps and fast idling to get more air flow from the fan?

The fan clutch seems to be working fine. Maybe I should flush the radiator & block & install a new thermostat to see if that brings temps down. PO last did it four years ago along with a brass radiator.

Thoughts anyone?

 

[ralphy1997]

I had a similar problem with my '88 FI Toyota Pickup for about a year. I changed the thermostat--problem solved. With all the computers on the LC, I don't know if they would compensate for something like that but you may want to check the temperature gauge to see if it drops on hills (not too likely in the summer) or has much fluctuation at all.

 

[S.CarolinaFZJ80]

Thanks ralphy1997. I will have to get on it when I get home this weekend.