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1997 firebird rough idle issues

9.2K views 5 replies 3 participants last post by  GTP231  
#1 ·
i own a 1997 firebird 3.8l v6 automatic with a 100,xxx miles.

i recently cleaned the iat sensor (unplugged) with maf cleaner and then the car started acting bad. the idle is extremely rough. codes were popping up left and right.

sense then we had a purge flow code always and i replaced the following items

the iat sensor, coolant temp sensor (2 years ago), iac sensor, and tps sensor replaced today. also replaced the alternator it was going bad. also cleaned the maf with the correct cleaner and cleaned the egr valve.

the car is only throwing one code now which is p0441 i think. it is the tps low voltage code.

im gonna test out the tps later when i get a chance. but i was wondering if i could get any help if anyone ran into this sort of problem.

i started it up and it idles to 1200 rpm then lowers and then rises up to 3000 rpms and stays there. then sometimes lowers and dies. for now it just starts hard then lowers to around 600 rpm and then it jumps up to 3000+ rpms and stays there.

any help would be greatly appreciated it. it is a daily driver and i had no problems with it til now.
 
#2 ·
Don't know much about 3.8 systems. Best I can do is to scan the pcm symptom chart in manual and e-mail it to you. PM me with e-mail address if you want it. I would suggest downloading the 98 service manual. While 5.7 engine cars made great changes between 97 and 98, 3.8 cars didn't. Look for thread titled 94 & 98 f-body service manuals, easier links". It's in this the 4th gen section near top of regular threads. Open thread, click link, download 98 manual. It should have the same pcm symptom chart I would send you.
 
#3 ·
i did the tps check and did not get any voltage from the first test. the 2nd and 3rd test were fine.

the iac, tps, and iat are new.

im gonna try and clean the iac inside and retest the tps. i cant figure it out.

i unplugged the maf and it still ran the same.

start it up, it runs high idle around 1200rpm and then drops almost sounding cammed and then it jumps all the way back up to 3000 rpms and stays there.

anybody got anything for me?
 
#4 · (Edited)
Yes, download the 98 manual and read the driveability and emissions section. Don't count new parts as being good, test them to make sure. Don't just check the sensors, also check all the wiring that goes with the sensors. Many sensors get a 5 volt reference signal from the pcm. Make sure you have 5 volts on the wires that need 5 volts. Unplugging the maf and throwing the pcm into speed density mode is not going to fix your car. What is going to fix your car is using the service manual, a dmm with high input impedance, a scan tool capable of doing running sensor scans, and your ability to test and understand the test results. But the most important thing to fix your car is the knowledge of how the sensors work, how they are used by the pcm, and how they are tied to each other. I haven't checked the 3.8, but I'm pretty sure GM does things pretty much the same as my lt1 car. You have to look at the pcm wiring chart because sometimes, power, ground or even the 5 volt reference signal is shared by more than one sensor.
To give you a example of how complex systems can be lets look at LT1 map sensor. It shares it's 5 volt reference signal with 2 a/c sensors. It shares it's ground with the same 2 a/c sensors and the IAT. So a fault in one of the other sensors can affect the MAP. These are the kind of things you have to know to successfully fix your car.
 
#6 ·
P0441 is incorrect EVAP purge flow. Check the vacuum lines to and from the Purge Solenoid, the Solenoid and check the MAP also since the pcm is watching it to make sure the EVAP purge is doing what its supposed to