High Idle problem, No I dont have any codes lol

[subjug4tor]

So heres the story. I drove to work yesterday (about 15 miles) with no problems, stay there about 4 hours, and leave to go home. I got in the supra, and a few blocks down the street, i notice something is different, but cant really tell what. no CEL or anything, so i figure ill look at it when i get home, and keep going.

I get within about 7 miles of my house, and notice that its idling at around 2000-2500, which apparently it had been doing the whole time, so i immediately pull into the walmart parking lot. I pop the hood, and cant see anything wrong, no stuck throttle cable or linkage or anything, and it seems to be running ok, so i baby it home, pull in the garage, and let it sit overnight (didnt have time to look at it).

I go back out today and check for codes, and find a code 51, so i adjust the TPS, and try again, no more codes, and the idle is down to around 1200 or so. Now I cant figure out whats wrong with her for the life of me. I thought, maybe its the ISC valve, so i pull the vacuum line to it from the accordion hose and plug both ends. idle goes down maybe 100 rpm, but its still well over 1000. i put the ISC back, and try plugging the brake booster line, that has no effect. i checked all my IC hardpipes, and sprayed everything with carb cleaner to check for leaks. nothing.

Another odd thing is that if i rev the engine really quick while its idling, it will rev up, then when i take my foot off the gas it will drop to around 900, then move back up to 1200-1500. I have a video of it doing this that i will try to post in a few.

Does anyone have any ideas as to what could be wrong?? The supe is my daily driver, and i need to get her back on the road ASAP.

 

[HommerSimpson]

id start lookin for a vacume leak... check all the IC pipes clamps ...hoses....

 

[subjug4tor]

I did that, everything looked good, plus i sprayed it all down with carb cleaner to check for a change in the idle, and got nothing

 

[jetjock]

Plug (or pinch) the ISC hose again. Then plug the PCV port on the TB. If the engine continues to run you either have pirate air or the throttle plate is open. It's as simple as that.

 

[subjug4tor]

Thanks JJ, Ill go try that later this afternoon.

Just a quick question, as im trying to get a better understanding of this, why would plugging the PCV port affect this?

 

[jetjock]

Because it's one of the three legitimate air paths into the engine. The other two are the ISC and throttle plate. Deprive the engine of all three and it can't run unless there's a leak somewhere. Checking the brake booster was a smart troubleshooting move but it's only useful after a leak is verified.

And fwiw spraying HC around is a crappy way to find leaks. Build a smoke machine. It'll be one of the smartest automotive things you'll ever do. It will find leaks in seconds in just about every enclosed volume the car has. You'd have to pry mine from my cold dead fingers...

 

[subjug4tor]

Ahh, i see. Ill go try that and check everything over again later, and post the results.

 

[jetjock]

It may not solve your problem but at least it'll eliminate vacuum leaks as the cause. Just be sure the throttle plate is fully closed, as it's supposed to be. If the engine dies start looking elsewhere. Timing, improper ISCV operation, and fuel control will all cause high idle. It's probably something simple though.

 

[subjug4tor]

ok, i just did what you suggested, and blocked the ISC and the PCV port. i started it and it was bogging bigtime, around 400-500 rpms, barely running. I assume that this means that the throttle plate is stuck open a bit? The thing is, it seems like its fully closing, i guess ill have to pull my 3K pipe and check it.

 

[jdub]

It should have shut off
That means you have pirate air getting in somewhere (assuming the TB plate is closed).

 

[jetjock]

Sounds like a leak alright and it has to be entering the engine after the TB. Keep that in mind when looking for it...

 

[subjug4tor]

well, i took off my 3k pipe and checked the throttle plate out, and it was all clean, nothing to block it.

I moved on to the linkage on the side of the TB, and checked all that out. everything looked like it had always been, mind you, the linkage had never been touching the stop screw on the bottom since i can remember. I did adjust the screw between the two rotating linkages until it touched the stop screw, thinking that was probably it, even though i remembered it being that way.

Next I inspected all the vacuum lines after the throttle body. i found a tiny hole in the one coming off the manifold to the cruise and all that, so replaced that section of line. everything else checked out.

I put it all back together, readjusted my TPS, and fired her up. purrs like a kitten. I still don't know if it was the throttle plate or that bad hose that caused it, but in any case, its fixed. thanks for the help, I couldn't manage without this site lol