1994 Pontiac Firebird vibrating

FIREBIRD94

MEMBER
1994 PONTIAC FIREBIRD
6 CYL
2WD
AUTOMATIC
177,000 MILES

My car idles(vibrates) hard when I put it in drive but not in reverse or nuetral. Usually it starts doing this after my check engine light turns on after about 5 minutes of driving but not always. Only does this when I pull up to a stop sign or I come to a complte stop while still in drive. Also 45mph and up my car shakes lightly mostly between 45-60mph and the rpms drop sharply right after I go past 45mph to around 1500rpms. Just got an egr valve put on. It calmed down the shaking at 60mph and up(alot bettr). It still mainly does it between 45 and 60 though. Please help

Thursday, October 8th, 2009 AT 7:08 PM

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

Your possibilities here could be one of the following:

Oxygen sensor
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

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Thursday, October 8th, 2009 AT 7:43 PM