My son's 1994 Cutlass Supreme (3.1L) hesitates and sputters on acceleration and during constant speed (you can see the tach fluctuate on the expressway and feel the transient power loss). Here are some things we tried so far (in order of attempt):

• replaced throttle position sensor
• found missing grommet at vacuum line from intake that tees-off to PVC and toward firewall. Replaced grommet and hesitation disappeared for a day or 2. This also solved some hard starting and a clanking sound that sounded like a shift solenoid when decelerating during revs while in park.
• replaced plugs
• tried injector cleaner additive and a 1/2 tank of premium (Mobil 93 octane)
• checked fuel pressure

I'm thinking my next steps may include ignition coils and possibly a fuel pump. I thought if it was vacuum once it may be vacuum again, but it seems intermittent. Appreciate any input.

 

I would change the plug wires before doing the fuel pump. You may also try the fuel filter, but I don't think that is the issue here.

 

Thanks Iflylow. The wires are reletively new. I had a neighbor who used to be a GM mechanic take a quick look. He suspects a #4 injector. Using his Tech1 he was able to toggle the EGR - so ruled that out. He also check spark and said all looked good. After trying to start the car and drive it back down the street it kept staling - so it went from a intermittent miss/hesitation to a severe hard start/stall problem.

 

Have you tried cranking it a little and then pulling the plugs to see if they are wet? You may have to pull all the plug wires to prevent it from starting.

 

Thanks for the suggestion. What direction are you taking? Should it be wet from fuel or from coolant getting by the intake?

 

I'm thinking that if the #4 injector is not opening, that plug will be dry and the rest wet with fuel.
If coolant was getting by, you would have a sweet smell and maybe white smoke from the exhaust. You should also notice the coolant loss.