1994 LT1 Trans Am idles way too low
#1
1994 LT1 Trans Am idles way too low
Hey, I have a 94 LT1 trans am that is stock except for headers and ls1 ram air air box with slp lid and it idles way too low after it warms up. When I start it in the morning before work it will idle fine above 600 to 750 but when it warms up it will idle around 400ish. Also when it is cold started in the mornings, I go to give it a quick throttle burst it acts like its getting too much gas and bogs itself down until it returns back to normal idle. I have replaced and cleaned and checked everything there is to think of on this car and it still idles low. New PCM, new MAF, new TPS, new O2, new opti, new plugs and wires, traded coils with another LT1 (that runs like a champ and idles correctly) for 30 minutes, cleaned iac, new air filter, even had it scanned by my brother who is a professional mechanic and the numbers all check out ok, open to closed loop. i noticed today that only half of the EGR was taken off, the solenoid and vacuum hoses are still attached. Any idea on what it could be causing this low idle??
Last edited by 94_LT1_TransAm; 12-09-2015 at 09:18 PM.
#2
TECH Addict
Hey, I have a 94 LT1 trans am that is stock except for headers and ls1 ram air air box with slp lid and it idles way too low after it warms up. When I start it in the morning before work it will idle fine above 600 to 750 but when it warms up it will idle around 400ish. Also when it is cold started in the mornings, I go to give it a quick throttle burst it acts like its getting too much gas and bogs itself down until it returns back to normal idle. I have replaced and cleaned and checked everything there is to think of on this car and it still idles low. New PCM, new MAF, new TPS, new O2, new opti, new plugs and wires, traded coils with another LT1 (that runs like a champ and idles correctly) for 30 minutes, cleaned iac, new air filter, even had it scanned by my brother who is a professional mechanic and the numbers all check out ok, open to closed loop. i noticed today that only half of the EGR was taken off, the solenoid and vacuum hoses are still attached. Any idea on what it could be causing this low idle??
#4
Yeah the water pump sensor is new, hrcslam. The iac readings im not sure about but the pcm was bad when I bought the car and it wasn't reading an 8th cylinder so i got a new one and fixed that issue right away, the maf and the tps were both bad so when i bought new ones of those the throttle response greatly improved. As for the opti, I bought a new AC Delco one and the idle smoothed out but was still too low.
#5
Any other ways I can check why my idle is so low, until I can get the iac readings? When the car runs it sounds like it has a hotcam in it every so often, but it is the stock camshaft.
#7
Yeah it will throw you in your seat once the car is rolling. it did stall once a while back but it never did stall after that. I've cleaned the iac once before to where it looked brand new, and the idle never changed.
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#8
TECH Addict
#9
What does something like that cost? I've never done a datalog before anyway, so how do I read all the information the PCM gives me? Sorry lol, i've never done anything to a pcm except to get a new pcm flashed by a dealership.
#10
TECH Addict
Get an ALDL cable (you'll need the OBD1 style) to usb, $60. The programs to Data log are free, Scan9495 and $EE Hack are good ones to use. Add in Tuner Pro RT (also free) and you can tune too.
#11
Ok so its not expensive like I thought it would be. Can the datalog be live streamed like a Genesis or a GM TECH2 is? For example, when you hook the car up to the datalog can you see everything from open to closed loop change and throttle position etc,etc? sorry lol ive never used this kind of stuff....
#12
TECH Addict
Ok so its not expensive like I thought it would be. Can the datalog be live streamed like a Genesis or a GM TECH2 is? For example, when you hook the car up to the datalog can you see everything from open to closed loop change and throttle position etc,etc? sorry lol ive never used this kind of stuff....
#13
Ok so I got my aldl cable in and it shows that my IAC upon warm up is at 0... But the minimum its supposed to be at, according to the PCM on the datalog, is 10 counts. When I checked the car on a cold start, the IAC was ok at around 30-50 counts. I even checked if it was a open or closed loop related problem with the datalog program override features and still no change in the IAC or idle after warm-up, any thoughts? I'm thinking vacuum leak possibly? BTW the minimum idle the PCM wants to be at in park is 550... That's a little low IMO, I can understand that low in drive but not park lol
#14
TECH Addict
Ok so I got my aldl cable in and it shows that my IAC upon warm up is at 0... But the minimum its supposed to be at, according to the PCM on the datalog, is 10 counts. When I checked the car on a cold start, the IAC was ok at around 30-50 counts. I even checked if it was a open or closed loop related problem with the datalog program override features and still no change in the IAC or idle after warm-up, any thoughts? I'm thinking vacuum leak possibly? BTW the minimum idle the PCM wants to be at in park is 550... That's a little low IMO, I can understand that low in drive but not park lol
#15
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I think you misunderstood hrcslams question...The PCM should have a idle target programmed in and that value does not change. It is the actual RPM target that the PCM is shooting to maintain at all times and it'll utilize the IAC valve (opening/closing) to maintain that target. If you are seeing 0 IAC counts and the idle is too low, that is where I'd start to look. The only time that you would expect to see 0 is if there is a problem with the idle being too high and the IAC is closing trying to bring it down. IAC should maintain a positive number to give room to open or close to maintain target. Also, what is target AFR?
#17
im pretty sure, since the pcm was flashed at a dealership, that the target idle is supposed to be what ever stock is. im not sure what the target afr is but i will do a datalog tonight after work and post it tonight if you guys would like? I use $EE hack to log.
#18
TECH Addict
If you are using Scan9495, with the engine running and the program hooked up and running, click on the blue "Actuators" button on the left of the program window. A new window will pop up, on the right side you'll see a bunch of "Idle=" Options. Pick one and see if the idle changes, I'd start with 800 and see what it does. You could've very well gotten a bad load from the dealership. If it's targeting 500RPM, it'll try and idle at 500.
If you are not using Scan9495, download and install Scan9495. This would be free and easy for me to help walk you through things.
Last edited by hrcslam; 03-10-2016 at 03:43 AM.
#19
I have Scan9495 (freescan) and $EEHack, how do I get my pcm tune onto my laptop? I have TunerPro RT also but have no idea how to use it lol, I could only get $EEHack to actually record data unlike Scan9454. I did use the actuator tab in Scan9454 and it seemed like the engine was going to shake out of the car lol. Like I said before, I even switched between open and closed loops with no change in idle.
#20
TECH Addict
I have Scan9495 (freescan) and $EEHack, how do I get my pcm tune onto my laptop? I have TunerPro RT also but have no idea how to use it lol, I could only get $EEHack to actually record data unlike Scan9454. I did use the actuator tab in Scan9454 and it seemed like the engine was going to shake out of the car lol. Like I said before, I even switched between open and closed loops with no change in idle.
I'm not familiar with EE Hack enough to remember if it shows you idle target rpm or not without looking at it and I'm at work right now. Maybe Steveo will chime in.
To load a tune in EE Hack.... That's hard for me to explain step by step without looking at the program. Try PMing Steveo_.