Not so sure what is happening. I had my stock throttle body increased to 53mm I experience high idle. When I start the car initially(prior to heading off in the morning) the idle is at 750rpm. Then I'll hit stop-and-go traffic and the idle goes to between 2000-1500rpm. Not so sure why. I have a 160degree thermostat and was wondering if the ecm is trying to compensate for the cold weather(it's been about 20degrees some days to 50degrees on others). Even after driving the car for about 4 hours I'm still getting high idle. Any ideas what happening or what I can do to fix it?

 

try replacing the IAC first. if that doesnt work, you'll need to get it programmed for the larger throttle body to bring the idle back down. Also, it could the the TPS is off a little bit, might check it.

 

Didn't think about having to re-program the ecm for the larger throttle body. The IAC motor is new from gm when the lt1 was rebuilt in 4/03.

What would th etps do as far as idle?

thanks for the info....

 

yeah I dont know what I was thinking when I said TPS, I don't think it will do anything for the idle since the computer can't control the throttle blades.

 

To understand this better....you originaly had everything working fine with no high idle until you had the throttle body enlarged?

 

yes, the idle was correct prior to the bore increase... very puzzled!

 

Five possibilites: (I started with two possibilites, but keep coming up with things to check.

1) Some aftermarket throttlebodies have adjustable throttle stops. Close the throttle down a bit. YOu may have a too much throttle leakage area.

2) YOu made need to do an IAC learn. Your larger throttle body will have different leakage area characteristics. Get to a dealer or somebody with a Tech II. There is a function to learn the IAC.

3) Make sure the pintle seat in the IAC port has no burrs. This is the area that the cone of the IAC fits into.

4) Make sure you have the correct IAC. I think the IAC motors are different between 1993 and 1994+

5) Make sure you have no vacuum leaks. Since it starts and runs fine when cold (open loop), and then goes to crap when you warm up (closed loop) any of the above items might be the cause.. .If I sit here long enough, I might think of a few more, but time to go to sleep.. Santa is coming

 

thanks everyone for there input.
Since I didn't ever replace the EGR valve(over the weekend ) I replaced it with a new one from GM. Ranked it and everything was fine. Took a long ride, thru the inner city - everything is perfect. Then yesterday I took it to work and bingo back again.
This morning I thought maybe the EGR vacuum line cam off or I didn't have it on at all. The I noticed the at when I moved the EGR solenoid the idle altered(up/down). Why so? is it because the vacuum line are attached - thus the leak? or is the solenoid beat? Picture is here

Speaking of vacuum leaks... when I turn the heat controls on I can hear a hissing sound when I put the heater control from cold to hot. I'm guessing that the vacuum leak within my heater controls is seperate from my high idle issue?

Any thoughts?

 

You may be homing in on your vacuum issue. Check to make sure the solenoid is functioning, and swap out the vacuum line. YOu may have a split that is not readily visible.

The hissing noise when you change heater modes is typical, the actuators in the HAVAC systems of that era were still vacuum dependent. If the hissing never goes away, you have an issue.

Did you look into your TB and setting the leak area??

 

beertestr, thanks for the notes. I was out of the state working and couldn't look into my issue just yet.

Another crazy question: Can I bypass the EGR system or reroute the tubing to go from the EGR to the side of the intake? and omit the EGR solenoid. But I gues the ECM is looking for codes of somekind since I have a speed density setup.

let me know when you can. thanks again for the info

 

Not sure if OBD of that era would have the ability to detect no solenoid. I would guess yes. The ECM only needs logic to detect an open circuit.


Before you make any more modifications, go check the things you already modified. Gotta check that IAC. Make sure the seat machined in the IAC has no burrs. Make sure it is clean.

Swap out to your stock TB and old IAC. See what happens. If all is good again, you found your problem.

DOn't make the mistake we all make and go try to mess with something else that you never touched, thinking that is the problem.

 

beertestr, I contacted the low$guy(from ebay) and said the following in his return email:

"There is an idle adjustment at the throttle linkage. It is a Torx-15 screw in the casting. The screw is used to set the "minimum idle speed" mentioned earlier. I am positive this screw exists and will need to be adjusted.

Vacuum leak is usually to result of improperly installed (or missing) gasket or hoses. The bearings have seals, so they don't leak.

If you can't get it going, you are welcome to return and we will check it out and replace if needed.

Thanks"

But where is the idle adjustment on the 95 lt1? I thought that the idle adjustment was on the TPS(as you mentioned). I'll have to give it a better look over tonight. yesterday night i was able to pull the t/b apart - clean the IAC housing as you made mention and then sprayed some brake cleaner to the metal part of the IAC. then put everything back together and in idle(at start up) at about 1100rpm then after about a minute it went back to 750/800rpm. Due to the snow i was not able to take it out for a test run. maybe over the weekend. I'll keep you posted.

BIG thanks for all your help and your input.


ps, i ordered an adj fuel pressure reg from TPIS - should be here on saturday that should work out well.
thanks again.