the car is a 96 z with 80,000 miles I recently changed the plugs opti, map sensor and coil. The car still has a hesitation and is dog slow. It doesnt misfire or back fire. It seems to run real good when you first start it in the mourning or the first of the day but then runs real sluggish when it warms up. I believe it runs like crap when it goes into a closed loop. I can also disconnect the maf sensor and it will get fast throttle response but runs sluggish. I also swapped the maf out and it also didnt do anything. Do you it could be the o2s I never changed them or something else?

 

Hey seemondemon, I have the same problem with my 94 Z28. When you start it up it runs great but when it gets to normal running temp it starts to bogg and sputter when you give it gas. My opti is a year old plugs are two years. However like you i have never change my O2's. Also when the car is running like crap it starts to rev up on it owns. Well i am trying to get it scan over the weekend. If I find something out I will let you know. GOOD LUCK!!



94 Z28 Teal w/ T-tops
1LE elbow
BMR strut tower brace
Moroso CAI
Car sound hi flow cat
Magnaflow cat back

 

I have the same problem

I just changed the opti, and that helped some, but there is still a slight stumble under load at operating temp. Its a 94 M6. I'm thinking it could be the 02 sensors, or a fuel filter. Is there anywhere I can take my 94 to get it scanned for free? Autozone only has the paperclip "scanner."

 

I'm having the exact same problems. I changed out the fuel filter, it helped some, but I still feel the stumble a bit. I'm gonna be moving to florida in a couple weeks, so I want to get this fixed before I have to take the car on a cross-country drive.

 

Same thing, this is what I've done so far:

Changed Opti, changed fuel filter, changed coil, plugs, plug wires, changed O2's, only 3 things left for me:

IAC sensor, but my car isn't coding for that.

Clean out the TB & change the 2 gaskets, while I'm at it clean out the IAC sensor.

EGR valve.

I've been hearing about the same stuff coming up over & over again, I really think it's the EGR valve, it only gets going or turns off once the engine is warmed up, that's all I have left, so...

 

You hit it on the head, the EGR works all the time. It also gets very carboned up from the exhaust gasses going through it. It usually ends up sticking open. You can do several things to check it. One is press the diaphagm with your fingers and see if it feels rough or sticks. You can unplug the vac line and plug it and see if it runs better. You can remove it and clean it or replace it and also make sure it didn't loosen up and start leaking air.

You may also want to change your TPS, their cheap and easy. I also recommend having your injectors professionally cleaned on the car. That is also cheap and easy and what a difference.

 

Hey guys this is a major problem. Gm needs to really address this situation. When I took it to Chevrolet they told me it was the manifold leaking oil into my opti. They quote me $1,800. To change plugs wires, opti, fuel filter and the intake leak. This is really crazy and expensive if this does not fix the problem.

 

I live in Atlanta and this same stuff started when the weather turned warm. I have done everything that you guys tried, and no luck. It feels and acts like a vapor lock, I even bought a new gas cap. I am tired of stumbling up hills too, I hope someone figures this out GM has no clue.

94 Z28

 

maybe bad gas???? or change the o2 sensors...cant think of anything else...