Tpi, Gone Wild

[81LT4]

ON monday, I decided to port the front of my plenium, on my 91 l98 man did i feel a difference, the car felt alot stronger, I ran it for about 3miles and no ploblems, got home and played with
it a bit more just to make sure i did not forget anything. I did
not mess with any sensors, I also bypass my water heater.
I cleaned my throttle body,and left my tps alone.
the next day, as i got in it to go to work, I felt the rpm raise
then lower, this happened for about 10 seconds. Now the
car sits at 1800 rpm, and wont come down. I drilled out
the little cap GM puts on the TB for ajustment to the rpm
even when i release the screw as far back as it will go the RPM
does not lower. this is as far as i've gone, no other ajustments
have been made. Has anyone ever had this happen?
PS. I reused the runner gasket,and put a new TB gasket.

 

[wichitacorvette]

i did the same and slightly cracked the lower openings to the iac holder..... so a lil air leaked making the map read wierd and the iac open etc etc....... also maybe the iac wires came loose from the connector? that happens sometimes too....... hmmmmm theres a couple other thins to look for but thats my initial thinking.......

 

[81LT4]

OK, i replaced the runner gasket with new ones, thinking that might work. well it did not. then I found out that i have to use a paper clip in the aldl, whatever that is for the IAC. Now when i
turn the car onit will idel at 900 the when i drive it a bit, it
will go down to about 600. where is the IAC? and what is the
ALDL? I even put my water heater hose back through the TB
to see if that was the problem, nope, not that either. I am still waiting for more help here. THANKS AGAIN WICHITA.

 

[Blue82]

Definitely sounds like air is getting in under the throttle plates. An open IAC port or leaking TB gasket could cause this.

 

[wichitacorvette]

ok, lets see, could be a faulty iac....... the iac in on the bottom of the TB. its the one witht the 4 wire plug on it........ unscrew it from the bottom on the tb and reconnect the plug. turn the car on, but DO NOT START IT. when you do you should see the little end move. also if you do the paper clip thing during this with the car on but not running it will move in and out constantly...... it might be somethign as simple as it is dirty. if it is, spray it with carb cleaner, but dont soak the electrical components........ let me know, ill think of more things if that doesnt work.......

 

[81LT4]

OK i'm gonna do the IAC tonite. this is just to weird, as for that whole nite the car ran like a champ, and all this crap did not start till the next day on the first start. What really ****es me off
is that i never, never ever once had a problem with this car
no matter how bad i dogged it or treated it. So i guess it's
true when your told (IF IT AINT BROKE DON'T F**K WITH IT)
I will post the aftermath of what happens tonite, I'm sure I will
need more help. THANKS TO EVEYONE WHO HELPED,and who
can still help.

 

[wichitacorvette]

most likely its the iac, the more i think about it, i got one when i originally had the xfire intake, and been through two in 6 months on my tpi.......... so most likely thats it........... theres also a way to test the wires on the plug, im going to go through my papers tonight and see if i can find my notes on how. let me know.......

 

[81LT4]

OK wichita, so i take it as if the IAC thing on the end does not move, this must mean it took a dump on me right. also when i cleaned th TB i used brake cleaner and i'm sure all the carbon
soot went all over inside the TB. so if it's dirty i will find out.
if I change out the IAC, I take it i won't have to make any ajustments to anything. just plug and play? let me know. thanks

 

[wichitacorvette]

brand new iac motor, plug and play, it should click like crazy with the ecm in aldl mode.......... (paper clip)if it doesnt get a new one........ my best guess...... you can also try turnign the end of the iac by hand to see if theres play........ sometimes it will loosen up to where its still useable....... still may want a new one anyways...

 

[81LT4]

Kool, Iam still at work, so when i get home i will perform
surgery on this troublemaker. If I cannot fix it,I will shoot myself
and go to hell. YOU'll know if you see no new tread what happend to me. thanks

 

[81LT4]

Well CRAP!!!!!!!!!!!!. I took off the IAC, turn the key with the
jumper on the ALDL and the pin flew right out of the sensor.
OK, no big deal, maybe it was bad. so i went to O"RILEY AUTO
PARTS. A new IAC is a special order and 75.00. Well i guess
I won't kill myself over this one. I let you know what happens tomarrow

 

[69MyWay]

Hey, 81...

Exactly which motor do you have in that car?

Is it an LT4 (based on the LT1, with the front mounted distributor), or is it a L98? If an L98, what year model and harness are you using?

The reason I ask, is there are different procedures for setting up the base idle, etc.

Let me know so I can figure out the best way to help you.

 

[81LT4]

This is my 1991 GTA 350 TPI, not my vette. I bought a HAYNES
fuel injection tech book to get some basic's. i have 3 TPI unit's
so i took the IAC off the 88 model unit and put it on the 91
it still does the same thing. it will not come down from 900
RPM. I sprayed WD40 all over the intake and the vaccum hose's
(EVERY VACCUM HOSE) and every crack i could find. there is no change in idle speed when i do this. This really sucks cause all
I did was port the front of the plenium,changed the top runner
gasket, and the TB gasket. When i took the car out after that
it ran very well, very strong, took it home turned it off, checked
everything one more time, then took it out again. The whole
nite was great. then the next morn, is when it happened
( TPI GONE WILD)


I still don't know if the 88 model IAC was compatible with the 91
THANKS 69, LET ME KNOW WHAT YOU THINK. (ANYONE)
PS. the vette 81, has a 96 LT4

 

[69MyWay]

Okay, I now I am not confused. I knew you had the LT4 in the Vette, but couldn't figure out how or why you would have swaped for a 91 L98.


Okay, It sounds to me that you are getting a vacuum leak that is artificially raising the idle.

This is a very easy thing to get on a TPI. Here is what I would do:

1. reinspect all the TPI runner bolts (upper and lower), to make sure I did not leave any loose. (tighten it if one or two found, crank and try the idle again).

2. If none found loose, I would go ahead and loosen the manifold and inspect the gaskets. I would be looking to make sure one of them didn't get pinched, or slip down allowing air to get sucked in after you warmed it up. (if problem found, correct it and try the idle).

3. Inspect every single vacuum connection on the manifold...follow it to the final destination (like the purge canister, etc)...looking for a vacuum leak. Pull your PCV valve--shake it, make sure it rattles--replace it if it has been more than 20,000 miles.

***HERE IS A GREAT WAY TO TEST***

If you or somebody you know smokes cigs...get them to light up a cig, and fix a long hose to your power brake booster or PVC inlet connection. Have them puff the smoke into the the engine. You should not see any escape...except out by the air filter. If you see smoke coming out of a vacuum T, the TPI gasket, throttle body...etc, you have leak.

4. If no leaks found, remove the throttle body. Clean out the idle air motor holes and chase the port with a scotch brite pad. Get it squeeky clean.

5. Here is the difference. A 91 should seat itself (at least on a Vette--I don't know about the F body).

--Ground your diagnostic lead under the dash where you can access your service engine soon. Unplug the Idle air motor. Fire up the engine and manually set the idle (you will have to keep it running manually), to where you want it. Shut down, unplug the diagnostic lead, replug the idle air motor. Turn the key on to run, but not start. Listen for the idle air motor to click and seat. Fire it up. Take it for a short drive at closed loop and let it set.

You should be there.

I know that is a lot of stuff, but crazy little problems like this usually take the most amount of time and trouble to diagnose.