here we go....

plugged the car in today and it gave me codes. P0121 and P0122. so????

i have a 408 iron block i just put in my car. its has maybe ten miles on it. I had the comp flashed so i could run the car, but it was too rich for my liking so i brought the car to the tuner, and he base tuned the 408 on the dyno.

i drove the car yesterday but only for a very short distance and it drove fine idled fine and everything.
drove the car today to my parents for thanksgiving, and two blocks from my house the car, i put the car in neutral and it started to rev up like the throttle stuck or something so i tap the throttle but it doesn't lower the revs. i shut the car off and pull over.

i play a little with the idle screw and i get the car to idle in neutral at 1500 rpm. drive it to my parents

go to drive home and same thing. i keep getting these random revs where ill be driving and then put the clutch in and it wants to raise to 3000 rpms and i shut the car off. on the way home i just got it there as quick as possible and turning onto my street i put it in 2nd and it revved up and it was like pushing through the brake.

just wondering what would cause a rev like that. TPS? IAC? the cam isnt that big (243/251) in the 408 so i dont know. is it a tune issue? the tune is SD. please any help is needed.

 

First you need to make sure the throttle linkage is going back to the stop. The cable could be out of adjustment, but when this is the case, it's very consistent (high idle).

Next thing is to diagnose the IAC system, and make that's working correctly. For that you'll need at least a scanner.

Finally, you'll need to look at the tune. This is the most likely culprit based on the inconsistency. Probably too much idle airflow in the base idle airflow table.

 

Thank you for your response. Just the person i was looking to get a response from.
when you mean the stop, you mean closed right?, if so then yes i believe the throttle body is closing 100%. i havent talked to my tuner and i dont have anything to verify electronically but looking directly at it it looks completely closed when the car is off and the linkage closed.

Now the IAC, do i need a program like EFILive or HPTuners to see whats up with that or is it like a multimeter test? i do have an OBDII reader, but that should no code for the IAC just the TPS. sorry for the questions and thank you very much for the answers.
Like i said i havent talked to the tuner. i plan on looking over the car tomorrow just to make sure all looks well. i looked briefly tonight and it all looked fine.

What can i do to check that all is in proper mechanical condition to work so i can rule out that before i blame the tune. most of these sensors came off my 75k LS1 so i can understand one out of whack.
Lastly, i believe that your name is ed from looking around on here, if so thank you again for your help and nice to meet you.

 

Sounds like a vacuum leak.Closing the blade lowered the idle a bit.

 

Bump for you! I'm having a very similar problem with my car and have had no luck finding the source of the problem

 

how would it be a vacuum leak? it only revs up when the car gets warm and it idles fine when the car is cold. it will go a couple blocks fine and then **** up. my understanding is that it would be constantly revving up which it is not but when it get stuck at 3000 rpms its stuck....until i kill the motor.

 

maybe it is a vac leak because i just started the car and it revved up to 2000 then i tap the throttle and it almost fell flat on its face. soooo any help would be great. i sprayed the carb cleaner all over it and it didn't really rev up higher but then i turned the car off and back on and it was at 3000 rpms. then tap gas again and falls flat on its face. i tried to delete the two codes and it wouldnt let me do it with my cheapy OBDII reader. any help appreciated....

 

slowhawk, when i close the throttle the idle goes higher......so what does that mean?? also the idle screw on my throttle body is all the way open as in no tension on the blade at all. should it be like that? also if it was a vacuum leak then wouldn't my tuner told me that before he gave me the car back. i mean my plugs were foul and they changed them so if there was more wrong wouldn't they tell me???

 

Also agree you have a vac leak. I had high idle problems during tuning but it wasnt any higher than 1500 rpm. Since its a fresh install, Id start looking for something that loosened up since the dyno. My first guess would be to look over the MAP. Just look over the intake carefully and any other vac connections.

 

everyone keeps saying that but nobody has told me how a vac leak has anything to do with the TPS codes i pulled.... so if someone will give me a relation then i will pull the manifold, other then that i have no belief right now that i have a vac leak.

 

Well then a quick check would be to reset your IAC and TPS. Unplug both, turn the key on but dont start for about 5 sec, reconnect then start.

Without a scanner, we are very limited to see what is actually going on.

 

If your throttle position sensor is not reading 0% when the throttle is closed, you will jump into the main spark table with a lot more timing. You will not have the benefit of spark underspeed/overspeed to help regulate the idle speed. This, coupled with too much idle airflow are most likely your problems. See it ALL the time.

 

........

 

ok thank you everyone for responding. pat g i got the cam specs from you. i have driven the car and it was very streetable.

anyways back to the issue. i took the manifold off and put clamps on everything in the back. also got the shorter valley cover bolts just in case, even though the manifold i'm using doesn't require them from my knowledge. going to fast and not disconnecting the manifolds MAP sensor, i broke the oil sending unit. i have one on the way and should be all good by this weekend.

im happy i pulled the manifold anyways because i wanted to put gasket maker all over the MAP sensor to make sure that was a good seal. i tried the TPS reset but to no avail, but did not do the IAC reset. When i get everything back on tight, i will do the reset.

I plugged in my OBDII scanner and tried to delete the codes but that didn't really work. the light wouldn't go off and i started the car and it did its normal high rev, i turned the car off plugged the sensor in and i got a P0122 and a P0122 Premature. My scanner sucks though, no Live Stream or anything. I plan on knowing for sure there are no leaks even though i sprayed the starter fluid and it didn't affect idle.

lastly i called my tuner and he said that my manifold was "non-campatible" with my car and that my sensor were all out of whack when he was tuning it. he said he haid never seen a car with that manifold, however he is a very reputable tuner here in the bay area, and am NOT knocking him. he said i could bring it by but i cant drive a car that idles this high on a california bay area street and not get pulled over, so im trying everything else first, can the car run without the TPS sensor. I do not know anything about tuning so sorry for my ignorance...

 

^^^^^^^^^^^^

 

What kind of manifold are you running that's not compatible?

 

Im running the Pro Products 96mm Typhoon intake ported and matched and a 95mm throttle body.....4 bolt style on both and cable driven.
the manifold is more then compatible.

 

Never heard of your setup before, google searched it and it looks pretty cool. Never seen a reverse geared tb before, and that is probably your problem. Your TPS is reading WOT at idle and 0% at actual WOT. Like stated above, if the pcm is not reading 0% tps at idle, the pcm will not go into the correct idle tables.

I would call up PP and ask them to see if they have had this problem and what they did to remedy it. You might have to modify the stock TPS sensor.

 

Timing is a giant issue as well. With improper idle/spark tables it will do weirddddd crap. Although Airflow in the TB is still the most common factor. IAT timing tables maybe jacked though. I saw someone mess up and add a value of 50* and his 408 went nuts.

 

i will look into both...my tb isnt reversed geared though. its just like a stock LS cable driven throttle body. it pulls the same way. i dont have the PP throttle body...so mines the same as a stock throttle body, in essence.