My 88 Formula 305TPI 5 speed now has an issue with acceleration.
4 days ago I noticed that the car would have a slight stumble when trying to maintain a speed. car would buck a little bit. Happens in all 5 gears at about 10-20% throttle.
2 days ago I changed plugs, wires, cap and rotor. Rotor button was stuck on the shaft so I had to pry it off. Put some silcone lube on the shaft and some got on the pickup.
Put everything together and it idled pretty good, but still had a very slight stumble, almost like a misfire, but it's not too rough.
didn't drive it that night since I was tired.
Took it out the next day and I noticed that it doesn't accelerate as quick as it used to and at about 70% throttle it feels like power kicks in. Pressing and holding the gas at about 50% and the car feels like it slows down. Press the gas more and it feels like vtec kicking in.

Before I start to buy replacement parts I was looking for some things to check first.
Car has 125K miles, was an Auto and is now a T5, have a chip for a T5 in there, took the smog stuff off and capped off the air tubes, I have the Park/Neutral wires tied together, and replaced the TB plate with another one the same night I changed the plugs and wires.
The air tube that goes to the cat has a clamp that is attached to the back of the head with some ground wires and that bolt is a little loose now. I am going to remove that air tube and tighten that bolt now since a friend mentioned that he had issues with his car when some ground wires were loose.

 

bad ground could cause all sorts or weird things, so thats a good start.

we'll assume your ignition is OK, after the tune-up; so try these things.

check the injector resistance, you may have an injector on its way out. even if they measure OK, its possible one or more could be clogged or not closing 100%.

check egr valve/system. if thats not operating correctly, it could be causing some issues if it's stuck open.

if the ignition is good, and the mechanical state of the engine is OK, that leaves air and fuel. you say it kind of wakes up, so a fuel deficiency doesn't sound like the case, which would be a clogged fuel filter or low fuel pressure. it also points away from clogged air filters for that same reason.

other than that, just check everything over. scan and see if the normal operating values look right.

 

You have described my same problem. Are you running rich?

Just so you know, my #7 injector failed and wouldn't let the motor start.

And on a side note, I replaced all of my injectors and I'm still having the same problem so I'm at a loss. I will be cleaning my IAC tomorrow and I'll let you know if that does anything.

Scott

 

same problem on my mom's '86 4-banger buick skylark... it's the busted headgasket.... that she refuses to let me fix b/c it's too "expensive" :lala:

 

Checked all the grounds and vacuum lines and still has the same problem.

It could be a bad injector(s), I'll check those tomrrow. I don't know if switching TB plates could have caused anything, but I will check that and make sure the gasker is in place correctly.

If all else fails, I am going to get a new distributor and coil.

 

IMHO this all sounds like a familiar issue that most fox-body Mustangs have. Check your throttle position sensor, sometimes they can become worn in particular areas due to daily driving and such. This will cause irradic accelleration like the way you are explaining. My second guess would be that your MAF sensor is contaminated. Test/check both of them and see what you find. My .02. -Bob