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burgett2103
09-04-2010, 11:01 AM
I went up to Cordova Dragway Park last night in Illinois. It was the whole midnight mayhem event and some friends came up with. About 10 miles before we got there I put 10$ worth of 91 octane in it.

Car ran perfect all night. After my last run, the engine was idling crazy high. It would accelerate while in drive without me touching the throttle all the way up to about 40 mph. In park and neutral, the idle is up at 2100 rpm which is ridiculous. when I put it in drive, it's still about 1200 rpm which is still higher.

It started doing this after one of my runs.

There are a couple things that I think are the problem, but I'm trying to figure out where to start:
1) Car has never ran over 89 or gas, so could this cause my air/fuel ratio to be thrown off or any other problems?
2) A vaccuum leak somewhere, or something wrong with my intake?
3) A MAF (Mass air flow) or TPS (throttle position sensor)?

Or if you think it's something else let me know, i just want to figure this out.

Car is a 2003 GT with 102,xxx miles.

FromTheInside
09-04-2010, 11:24 AM
Octane shouldn't do it. I have ran full tanks of 93 in mine before. I had a weird misfire I couldn't find so for the hell of it when gas was $2 a gallon, I ran an entire tank filled from 1/8. I don't know if it'd make it go this high, but what about your IAC sensor? (Idle Air Control Sensor) Maybe it is stuck open. If you suspect a vacuum leak (which I doubt because your engine should be surging if this much air is entering the engine past the sensors) then get some starting fluid and spray around the mating areas such as between the UIM and LIM, vacuum lines, etc.

If your idle is steady, The extra air is probably coming through the intake before the TB and MAF sensor. I think you should remove the IAC valve from the back of the TB and check its condition. Get Q-Tips and some degreaser and clean the hole where the IAC goes as well as the valve itself. Also, suspect a problem with the EGR valve as well. Any codes?

Pull off the intake tubing and check the throttle plate. Maybe it is getting stuck in a partially opened position. When my friend and I changed his starter on his old Aurora, his car idled at 2100 rpm and we found that we didn't click the cruise control into the throttle all the way so it was pulling the plate open. Maybe yours is getting hung up on something.

Many things could be the cause and it may even be simpler than all I am saying. Start here and see what you find.

FromTheInside
09-04-2010, 11:29 AM
Also, here is the TPS relearn procedure.

Credit to AaronGTR for typing this up

Turn ignition key to on (but don't start engine) and leave it for 10 seconds, then turn it off for 10 seconds.
Then push the pedal down as far as it will go, turn ignition key back to on for 10 seconds again, then turn key off, then release pedal and wait another 10 seconds.
Repeat this 2-3 times to make sure it's got it. If you have a scanner you can verify it. With the ignition on and foot off the pedal it should now read 0% throttle, then push it down and the percent should rise until you are at 99-100% at WOT position.

boost21
09-04-2010, 11:52 AM
My guess is a vacuum leak somewhere.

350rs
09-04-2010, 12:12 PM
The how to from aaron up there worked for me. when i put a NEW TPS in mine.

My car did 100% what yours is doing now. Steady acceleration clear up to about 40. Idle around 1300 or so or drive and close to 3000 in park or neutral.

Check out all my problems with it. Search " TPS relearn" and look for my thread, should be the first one.

burgett2103
09-04-2010, 01:11 PM
The how to from aaron up there worked for me. when i put a NEW TPS in mine.

My car did 100% what yours is doing now. Steady acceleration clear up to about 40. Idle around 1300 or so or drive and close to 3000 in park or neutral.

Check out all my problems with it. Search " TPS relearn" and look for my thread, should be the first one.

that seems exactly it. I idle up to about 40 mph or so on it's own. I had narrowed it down to tps or iac. but, i may be doing this tps relearn now.

thanks guys i'll see what happens

AaronGTR
09-04-2010, 05:16 PM
Yeah, fuel octane would have no affect on this at all. My guess would be a problem with the TPS or IAC valve. It could also be a vacuum leak but it would have to be pretty substantial to make it idle at 2100 rpm and you'd probably hear it whistling. It would also throw your fuel trims off a good bit (if you have the ability to scan them). TPS relearn would be a good idea. Check and make sure your throttle plate is returning all the way to the closed position before you do it though.

Mac0083
09-04-2010, 06:07 PM
i also had this problem before. i changed TPS and IAC. iirc, the car resets something at 60mph? after replacing the TPS and IAC, it still idled high until i ran it on the highway to 60 or so mph. my rpm was 3000+ in neutral, ran to 50 or higher on it's own.

also, i've ran 93 gas before, no problems, just better fuel mileage!

burgett2103
09-04-2010, 09:47 PM
yeah, i never ran over 89 before so i had no idea if i needed my pcm programmed for it or not so I didn't know if that was an option.

But on my iac, does stuck open mean that spring piece is sticking all the way out or means it is sticking in? i took it out, pushed it in, put it back in, started car, turned off car, took it back out, and it was all the way out. It seems really dirty anyhow, so maybe a new one is a good idea. and for the tps, i started car with and without it and did same thing. Also, is the tps just the black piece with the harness, or do i need to get the entire unit out of the throttle body?

Would trying a tps relearn before buying parts be a good idea or a waste of time?

Mac0083
09-05-2010, 06:04 AM
TPS is just the black round piece with the cable hookup. it's all external. doing a relearn, even if it was a waste of time, is just a few minutes. can't hurt.

when i took my IAC off, i couldn't push the spring in, or pull it out. but when it is sticking all the way out, that means that the valve would be closed on the car. if you pushed it all the way in, then you had it all the way open when it was put on the car.

burgett2103
09-05-2010, 05:22 PM
so being stuck open means its jacked then?

350rs
09-05-2010, 06:27 PM
can you turn your car off and have it run properly? i used to kick it into neutral, turn it off and back on and sometimes that would make it idle more correctly.

i suspected my IAC as well. but that was never the problem. Wouldnt hurt to clean the pentle and its seat though. Just use some carb cleaner. Q-tip for the seat with cleaner on it.

burgett2103
09-05-2010, 07:21 PM
haven't tried that, but i think the iac is shot. i can try that though to possibly save some money

WidbyJ
09-06-2010, 12:44 AM
IAC - not EVER supposed to move it in and out by hand, gears get stripped. Clean the throttle body fully and install a new IAC. May need to recalibrate the TPS too...

Mac0083
09-06-2010, 07:23 AM
IAC - not EVER supposed to move it in and out by hand, gears get stripped. Clean the throttle body fully and install a new IAC. May need to recalibrate the TPS too...

that's what i thought. mine wouldn't budge, not in or out. pretty sure that's your problem

burgett2103
09-06-2010, 08:05 PM
okay then that's my answer. i took it out, and i could push it all the way back in. and the spring and bolt with the threads in it popped off too. so i am going to assume i need a new iac.

will i have to do a relearn procedure on this too or install and good to go?

sorry for the questions, never had a problem like this before

burgett2103
09-12-2010, 05:20 PM
attention grandamgt forum, it is not the IAC.

replaced iac this afternoon and still has that same high idle problem. The idle gradually goes up as the car runs. I tried unplugging the tps and starting it and it idles at like 2500 rpm. I plug it back in and it continues to idle and it will eventually get up to 2500 rpm if i let it ran. I checked vaccuum lines and don't see a problem anywhere with that. Any other ideas?

Mac0083
09-12-2010, 06:42 PM
like i said, i changed my IAC and it still ran a high idle, screwed up, until i ran it on the highway.
cruise about 60mph or higher for a minute. my fast idle literally fixed itself all at once when i pulled off the freeway and stopped at a light. the idle revs just dropped from 3000rpm to the normal ~600rpm. been normal ever since.


my daily drive routine at the time was a series of backroads, and the car never went above 45mph for months. ironically, since the car was acting particularly horrible that day, with 3000 rpm idle, i jumped on the interstate to head over to the dealership. after leaving the interstate and while sitting at the stop light on my way to the dealer, it fixed itself.

WidbyJ
09-12-2010, 10:56 PM
i jumped on the interstate to head over to the dealership. after leaving the interstate and while sitting at the stop light on my way to the dealer, it fixed itself.

Like taking a pet to the vet, halfway there they cure themselves!

OP - Changing the IAC and calibrating the TPS (again) should have taken care of this. Are there ANY other lights on, bouncing in the tach or surging issues that might give more of a clue? Have you verified, by hand and eye, that the throttle plate is closing properly? Have you check for intake leaks using carb cleaner or? EGR could cause something similar if your engine uses it...

Wish I could help more, any chance you could post a video of it? Sounds can tell a lot. Good luck.

burgett2103
09-15-2010, 02:18 PM
i haven't tried relearning tps, but all i've done is replace iac and take it for a ride. still idles high. I've noticed it shifts gears differently than it used to too. the throttle kind of bounces while going 65-70mph, so could tps be my next solution?

burgett2103
09-15-2010, 04:17 PM
just replaced tps and did the relearn 4 times. still nothing good.....

grandam3400
09-15-2010, 09:22 PM
Are you sure you dont have a vacuum leak? I had a very similar problem and mine was a vacuum leak. Are you hearing anything different under the hood now? A loud sucking noise from anywhere?

burgett2103
09-16-2010, 12:26 PM
only time i hear something different is when i do take a vaccuum hose off. But, i'm not sure what it's called, but there is a vaccuum line that goes from front valve cover to a U shaped vaccuum hose that goes into a black piece. it sits behind the throttle body and when engine runs it sucks the hose shut. idk if that has anything to do with it or not beause i tried a different hose and it doesn't suck it closed but still idles sky high.

Mac0083
09-16-2010, 01:16 PM
that's odd... i don't think a vacuum line should be shutting from the suction. maybe a symptom of the true problem, but not the cause of it. the line coming out of the front valve cover is just part of the positive crankcase ventilation PCV system.

have you tried the brake parts cleaner idea? you spray the brake parts cleaner around jounts, seals, anywhere that could have a vacuum leak, and if the engine revs (unfortunately, yours is already revved pretty high) if the engine revs, then you have found where the vacuum leak is at.

sorry Nick, but i'm out of ideas on this one. other than the IAC and TPS, i don't know.

burgett2103
09-16-2010, 02:02 PM
thanks for all the help, i really appreciate it. I just brought home a new MAF and that didn't help either, so i'm taking that back and getting 100 bucks back. Tomorrow i'm going to take 65mm tb off and put stock one back on, just to see if i could possibly be the throttle plate not completely shutting. I may try that vacuum test with the brake cleaner tomorrow too.

Anyway, does a blown gasket necessarily have to leak? I ran my car 7 times, and engine was somewhat hot each run. After my last run is when i got the problems. So, i'm not sure if I have a slight suction leak from a blown gasket, or what.

burgett2103
09-19-2010, 06:46 PM
car is fixed. I disconnected battery, reinstalled my stock throttle body and connected it all back up and it was normal. I was like wow, wtf, my 65mm throttle body better not be somehow jacked. Took it all apart disconnected batteries again reinstalled 65mm tb and it was all good. I think it was because I never disconnected battery all the way before so the pcm never really knew i had any new parts. I ended up only replacing iac and tps. Thanks for the help guys, especially you mac, really appreciate it.

Mac0083
09-19-2010, 07:53 PM
you are more than welcome, but i never disconnected my battery when doing either the TPS or IAC, or at a much later date the 65 TB. maybe i did subconsciously because i had tools sitting on the battery and didn't want to short anything out, but definitely not on purpose to reset anything.

glad you've fixed it. and see, you didn't even need our helplol

was this the first time that you've unhooked the battery?

burgett2103
09-20-2010, 12:55 PM
i only unhooked positive, but i ended up doing both this time