2001 Firebird 3.8L Rough Idle?

**FireBird126** · 02-20-2015, 10:12 AM

Ok so here's my issue, hopefully one of you can help me. I had my plugs replaced a little over a year ago(along with fuel filter, PCV valve, and breather) so I know they're good but I recently just replaced my spark plug wires, ignition coil packs, alternator, air filter, and done an oil change. These were all needing replacement and she runs so much better, a LOT more power and better gas mileage. But one issue still remains, it still idles rough. When I'm stopped at a light the engine vibrates more than it should, I mean it shouldn't be able to be felt like that, it should just run smooth. I've noticed that when cold and I put it into drive and coast without hitting the gas it kinda lopes instead of running smoothly. I also noticed a time where after driving it around a lot and being full temp it loped when I started it back up only a 5 minutes later and it was loping badly until I hit the gas. It doesn't do that at stop lights just shortly after starting it sometimes... Anyone have any idea what it could be that I could check?

I checked my MAF sensor and it looks clean, no fuzz/debris in it and the hot wires were intact and not damaged. That doesn't rule it out I suppose...

**99ss405** · 02-20-2015, 02:44 PM

Have you cleaned your throttle body ? id spray it down really good ... check the iac also

**theorangeguy** · 02-20-2015, 03:10 PM

Any check engine codes being thrown?

**FireBird126** · 02-20-2015, 04:07 PM

No check engine codes. I had one not long ago for an evap leak but I got it fixed. What type of cleaner would I spray the throttle body with?

**99ss405** · 02-20-2015, 04:09 PM

I just use red can of CRC throttle body & intake cleaner

**FireBird126** · 02-20-2015, 04:21 PM

I'll look into that. I just sprayed off the MAF sensor with cleaner and it didn't seem to make a difference but all I did was idle it so maybe it needs to be driven a bit for that to take effect if it was dirty. So to get to the throttle body you have to take off the MAF screen and MAF sensor first, right? I don't have it right by me so I can't look to investigate atm.

**99ss405** · 02-20-2015, 04:30 PM

no .. look at the hose clamp on intake hose closest to the engine. take it off. If your not familiar with this part get someone to press gas pedal to the floor with car shut off. A circular blade should open. spray out side and inside of this piece well with engine off let sit for 5 min an start

**FireBird126** · 02-20-2015, 04:34 PM

Thank you very much. I will try that also. The car has 135k miles on it, so it's quite possible this never ever got cleaned(considering when I got it almost no maintenance had been done).

***SMWS6TA*** · 02-20-2015, 05:44 PM

is it acting like a vacuum leak? high idle? the pcv love to clog up and the vacuum lines go to crap.

***SMWS6TA*** · 02-20-2015, 05:45 PM

also make sure you use maf cleaner only on it. anything else and you can kill it. never touch it just spray, let air dry.

**FireBird126** · 02-20-2015, 08:25 PM

Originally Posted by SMWS6TA

is it acting like a vacuum leak? high idle? the pcv love to clog up and the vacuum lines go to crap.

No not really, once it warms up it idles pretty normal. I haven't paid really close attention to that but I want to say 700 rpms is where it idles.

Originally Posted by SMWS6TA

also make sure you use maf cleaner only on it. anything else and you can kill it. never touch it just spray, let air dry.

Yup that's what I used.

**Whamhammer** · 02-20-2015, 08:55 PM

Originally Posted by FireBird126

No not really, once it warms up it idles pretty normal. I haven't paid really close attention to that but I want to say 700 rpms is where it idles.

Yup that's what I used.

Check to make sure the IAC motor isnt going bad or the passage hasn't been gummed up.

Another thing to check is intake manfiold leaks, they were frequent on this motor for FWD applications, never really saw it on the RWD's but its work checking.

**pajeff02** · 02-21-2015, 05:59 AM

I'll second (or third) the recommendation to clean the throttle body. Be gentle, but hose it down good and pay particular attention to the area where the blade seats against the body in the closed position. Use lint free paper towels, like the blue garage towels, or a cotton cloth to wipe things down as you clean it. I also use q-tips to get into any tight areas.

**theorangeguy** · 02-21-2015, 07:03 AM

Could the intake gasket be the issue? Sounds like something is expanding and seating correctly after everything warms up.

**35th-ANV-SS** · 02-21-2015, 07:08 AM

Originally Posted by theorangeguy

Could the intake gasket be the issue? Sounds like something is expanding and seating correctly after everything warms up.

That's my guess. My 3.8L had the same thing happening when I owned it.

**raynor139** · 02-21-2015, 07:17 AM

My old 3.8 had a bad gasket too that would do something similar.

**theorangeguy** · 02-21-2015, 07:22 AM

Originally Posted by 35th-ANV-SS

Originally Posted by theorangeguy

Could the intake gasket be the issue? Sounds like something is expanding and seating correctly after everything warms up.

That's my guess. My 3.8L had the same thing happening when I owned it.

Me too. I've done just about everything you can do with a 3.8 unfortunately...the plus side of that is that I know them pretty well now lol

**35th-ANV-SS** · 02-21-2015, 07:31 AM

They're stout motors. I drove mine through hell and back. Put 200K+ miles on it and finally sold it with 218,XXX on the clock. Still running to my knowledge lol.

**theorangeguy** · 02-21-2015, 07:34 AM

Originally Posted by 35th-ANV-SS

They're stout motors. I drove mine through hell and back. Put 200K+ miles on it and finally sold it with 218,XXX on the clock. Still running to my knowledge lol.

I know for a fact one of mine is still running because it went to somebody I know when I got rid of it. It's well over 240,000 miles now.

**0rion** · 02-24-2015, 06:38 AM

I agree with what others have said.......clean throttle body, MAF, and check for vacuum leaks in the lines going to the intake. 14 year old vacuum lines tend to start cracking and what not. It does sound more like an airflow issue versus a fueling issue. It does it when the car is completely cold? If so that would pretty much rule out O2 sensors as they haven't closed the loop when the car is cold so it would steer me towards the MAF and vacuum lines. Hosing out that throttle body is always a good idea since it's probably due for a cleaning anyhow.