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1998 Pontiac Firebird low idle

Tiny
TYRANTXZERO
  • MEMBER
  • 1998 PONTIAC FIREBIRD
  • V8
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
I start the car, it idles crazy goes up to 2500 rpm then back down to 500 till it finally reach idle at 800 rpms. I let it warm up and put it into drive. I stop the car with brake the cars idle goes down to 500- 600 rpm. The car shakes and sound like it dying. Then if I want to change it to reverse it stalls. Pontiac trans am 98
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Saturday, December 29th, 2007 AT 4:15 PM

11 Replies

Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
I would like you to clean out the throttle body and also check your IAC the pintle should be moving freely. Does the car run rough when running?
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Saturday, December 29th, 2007 AT 6:11 PM
Tiny
TYRANTXZERO
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  • 33 POSTS
Does not run rough, but the oil pressure also goes down. I replaced the iac and I cleaned out my throttle. Alot of carbon build up there.(I thought that was the problem but no dice). I was having a secondary air injector malfunction but fixed that.(The smog pump was broken, water inside). Could it be my egr valve.
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Saturday, December 29th, 2007 AT 7:02 PM
Tiny
BLACKOP555
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Yes, that is what I was going to have you check next.

Also check your PCV valve.
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Saturday, December 29th, 2007 AT 7:38 PM
Tiny
BLACKOP555
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Also how about your plugs and wires? Make sure the plugs are clean and properly gapped. Never hurts to change them. You also may want to change your fuel filter and clean off your MAF sensor.
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Saturday, December 29th, 2007 AT 7:43 PM
Tiny
TYRANTXZERO
  • MEMBER
  • 33 POSTS
I changed the fuel filter, tps sensor, cleaned the maf sensor. But problem remains. I have not checked the pcv valve but will tomorrow. Could it be the speed/distance sensor, or maybe the map sensor. Thanks for help so far, any other suggestion would be great. ((((It's now stalling when I stop but the rpms are not going wacky when I start the car anymore.))))
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Monday, December 31st, 2007 AT 1:17 AM
Tiny
BLACKOP555
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Ok, I want you to look for vaccum leaks now. Take a can of starting fluid or carb cleaner and start the car and slowly spray ever vaccum line and around the manifold, if you find a spot that increases the idle or decreases it somewhere replace, if its around the manifold replace the intake manifold gasket.
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Monday, December 31st, 2007 AT 9:58 AM
Tiny
TYRANTXZERO
  • MEMBER
  • 33 POSTS
I did what you told me with the starter fluid but no increase or decrease in idle. I checked my egr valve but it seems to be working. Could my transmission affect the idle. When I shift it goes glunk then and my car joint back or fore demanding on which gears its in. Then my idle goes to stall then to 600 rpms.
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Monday, December 31st, 2007 AT 6:08 PM
Tiny
BLACKOP555
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Tranny would not affect the idle, and the reason why your vehicle is clunking when you shift it is because it is not running properly. I belive I went over everything that would cause that ill list them again and see if we forgoton any thing.

Bad IAC valve replace, new gasket.
Vaccuum leak, spray vaccuum lines and intake manifold with carb start fluid to find.

Bad EGR clean or replace, Possible DPFE bad.

Out of Ignition timing.

Replace PCV valve and check/replace the rubber elbows and pipe if cracked or cry rotted.

Restricted Exhuast system, hook up vaccuum guage and let car run at about 2500 rpm, if more gas is needed to maintain 2500 rpm over time or vaccuum pressure falls slowly restricted exhaust system.

Bad MAF, clean if not badly damaged or replace

dirty fuel injectors, bad plugs, bad wires *if distributed change rotor and cap*

clean out Throttle body and check for leaks on air intake hoses with carb cleaner or starting fluid sprayed on them. Also check aroudn throttle body for leaks same way.

Go over those all again

New Fuel filter.

Thats about all I can think off.
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Tuesday, January 1st, 2008 AT 10:20 AM
Tiny
TYRANTXZERO
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  • 33 POSTS
Would the oxygen sensor affect it. I havent changed them. I had my catalyic converter removed a while back. One of the sensor is need the welding area.
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Tuesday, January 1st, 2008 AT 12:54 PM
Tiny
BLACKOP555
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I am not sure it would cause that bad of a problem but it would definetely affect the driveability.
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Tuesday, January 1st, 2008 AT 12:57 PM
Tiny
TYRANTXZERO
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  • 33 POSTS
1. I changed the hose to the pcv valve. Now it does not have crazy idle at the start up.
2. Changed throttle position sensor ( if throttle stop is high then my friends TA would that affect it)
3. Idle air control valve- new- am I suppose to do anything other then reset the ecm when installed?
4. Changed speed/distance sensor- someone told me it would help.
5. I clean maf.
6. I check for vaccum leaks with carb( but will do it again tomorrow)
7. I checked egr valve and hose- ( I did a mod a while back with end that is in the manifold( I cut off the bottm half(Had a little hole now a big one) for less air resistence).
8.I changed smog pump( now my car sounds like it has a turbine on it, well that what my friends tell me)

I notice that when I turn air condition or heater the rpm rise high to abut 1200 rpm when in park, but drop down to good idle range. But when I changed back to park it Idle crazy till it goes to regular idle, is that bad?
Thanks for help, and happy new year.
I am going to clean oxygen sensor tomorrow and also look for vaccum leak again.
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Wednesday, January 2nd, 2008 AT 9:52 PM

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