nascarnate326

iTrader: (1)

Sometimes my car will idle at a gauge indicated 1500-1800 rpm as I am coasting at 4 mph or at 40 mph.

Sometimes it drops back down to 1200 where it should. Typically does this after I have been on the gas real good.

I have replaced the iac, and tried the resistor mod for my air incoming temp sensor.

98 z28, 224 cam, tuned my mad tuner.



Why does my car behave perfect some days and horrible other days?

inssanity21

iTrader: (16)

do you have a fast? mine was doing this and it was because the MAP sensor would come out enough to cause a vacuum leak and then come back in to be fine.

nascarnate326

iTrader: (1)

Ported ls1 intake. I know, it was done in 2001 before fast was really a big brand.

I'll check it though.

shep28

iTrader: (4)

I had that issue after my cam install and drilled a hole in my tb butterfly. Solved

nascarnate326

iTrader: (1)

My car has a hole in the tb blade already. Anything else?

SSdreamz

iTrader: (3)

subscribed...when you come to a complete stop does it settle down and idle perfectly?

nascarnate326

iTrader: (1)

Yes. Usually takes about one or two seconds after I come to a stop and then it idles at 850(via OBDII port) like my tune says it should.

I have also replaced the entire PCV system so I am 100% positive there are no leaks or issues with that system.


Going to check the MAP sensor on the back of the intake tonight when I get home from work. Really sucks because I thought I had this care running perfect but it surges a little bit randomly and it does this goofy idle wile coasting or going slow. Some times its like a cruise control in second gear at 1800 rpm while going through a parking lot.

demonspeed

iTrader: (7)

Definitely sounds like a vacuum leak. Check the hose that runs from top of TB to passenger valve cover. I found that my throttle cable bracket bolt had rubbed a small hole and caused a leak in mine.

Also check the HVAC lines that pull vacuum from the back of the intake (they run behind the passenger strut tower).

slow96ss

I've been having the exact same problem for a while now but haven't had a chance to go digging for the problem. when I pull mine out of gear, idle jumps straight to 2k rpm and rubber bands between 1700-2000rpm till I come to a complete stop. Thinking mine is a vac leak though. hope your able to figure it out.

Spink

iTrader: (1)

You've probably already done the idle relearn trick but if you haven't give that a shot. I had my battery disconnected and I had the same problem after I hooked it back up. Did that relearn and all is good. Mine does that every time I disconnect the battery for any extended period. I have a ported throttle body.

nascarnate326

iTrader: (1)

I have no did it, care to share?

Replaced Throttle Position Sensor..no dice.

Went to pick up a pizza and it was doing its 1800 rpm cruise control/high idle, turned car off for maybe 45 seconds to go in and get the pizza. Came back out fired it up and it drove perfect all the way home.

What on the car could be so inconsistent?

josephholtinsurance

iTrader: (1)

that sound like we have the same car. My car is doing everything you have described. I replaced the pcv hoses, IAC, TPS. Nothing has worked for me. The only difference is that man idles worst when o turn the AC on.

Spink

iTrader: (1)

https://ls1tech.com/forums/general-m...e-relearn.html

Post # 14 works for me.

Usually I can just get away with doing the IAC relearn though. I'd try that first if you haven't tried that either.

Just unplug the three plugs going to the intake before the throttle body and turn the igition to run for 30 seconds without starting it while the plugs are all unplugged. Turn the key back to off and take it out of the ignition. Plug the plugs back in and start it. It may sputter a little at first but should smooth out. If it's not better do it again with the a/c turned on. If that doesn't work go to post #14 above.

In tyhe 9 years I've had my car I've probably had to do this 20 times and the IAC reset usually works 90% of the time. When it hasn't then post#14 worked the other 10% of the time.

If it doesn't work I think the others probably are right with the vacuum leak assessment. Start the engine when it's cold and get a can of carb cleaner and spray it around the intake and all the vacuum hoses. If the idle changes you've found your leak. Never seen it happen but if you spray the carb cleaner around on a hot engine it could possibly ignite so make sure engine is cold when you do that.

nascarnate326

iTrader: (1)

Did Iac reset and it seemed to fix it for the most recent drive, Ill try it again tomorrow.

Spink

iTrader: (1)

Cool. Once I went to the ported throttle body was when I had to start doing this and it always seems to work. Never have a problem until I disconnect the battery for awhile though then my idle does that same exact thing most of the time.

nascarnate326

iTrader: (1)

Well the car is still doing it...very odd.

Seems like after I get off the highway it is fine..more of an in city issue.

Everything left to try is expensive, might have to live with it for a while unless someone has another idea.

Perhaps it really is in the tune, but I figured mad tuner would have his **** together.

Spink

iTrader: (1)

One other thing you could possibly try is checking your coolant level if you haven't. Ive seen that screw with the idle on these cars more than once. Sometimes the simplest things can cause problems you'd never suspect. Worth a shot at this point.

HioSSilver

iTrader: (8)

You can adjust your throttle cracker to control op's issue. I turned mine off.


another issue is the vacuum leak....except the leak is the extra area of throttle blade crack from the larger tb. I fixed mine by sealing it better with a small amount of epoxy around The throttle blade.

nascarnate326

iTrader: (1)

What is the throttle cracker? Got a quick how to?