Driving me NUTS!

[jesserose17]

My 94 GT has been missing/bucking at partial throttle - usually between 1200-1800 rpm. I have replaced ECT and O2 sensors. I've cleaned IAT sensor. New Air Filter, New Spark Plugs (only 3 months old) and 20k miles on spark plug wires. Replaced MAF 20k miles ago. At WOT, it takes off smoothly - no missing at all. So apparently that rules out the fuel issues. What am I missing?? No Codes. It has 111k miles on it now.

 

[DFG 5OH]

clean the maf???

 

[grrrrrrr]

could be EGR...

 

[jesserose17]

clean the maf???

Wouldn't using a carb cleaner ruin the MAF??

 

[jesserose17]

could be EGR...

How would I determine if the EGR is faulty?

 

[DFG 5OH]

Q-tips and ethyl alcohol. And be very careful.

 

[jesserose17]

Q-tips and ethyl alcohol. And be very careful.

thanks for the tip... anything else should I check in case this doesn't solve the problem?

 

[gcomfx.com]

Doe it have the hesitation when sitting while you have your head under the hood? Mine started like that and got really bad and wouldn't idle at all. I deleted my EGR and it cleared up MOST of the issue. I figured out it was my EGR when playing with the throttle. I could see the EGR diaphram wasn't moving... I gave her hell a couple of times and the EGR diaphram moved... then the car idled fine. I lucked out seeing what the problem was.

I still have a hesitation or buck "some" days. I personally am leaning towards plug wires for me. It's about the only thing I can think of that might move around and cause the car to behave eratically.

I still have an idea floating in the back of my head on a reason... I'm not a mechanic, but I have to ask. Do you have underdrive pullies?

My crazy mind makes me keep thinking about:

When my front rotors were warped we rebuilt my rearend and replaced the broken ABS sensors. Which activated my ABS system again. My car honestly ran crappy when we fixed the ABS. I replaced the rotors and my car ran better. Strange huh? Watching the charge guage... before and after the rotor change was interesting. I think my rotors were warped enough my ABS was trying to engage, and dropped my voltage in the car causing it to run bad.

I feel like my car isn't getting the charge it should and is really noticable at idle or just above. When I get past that 2,000 rpm range the charge guage goes up and things seem to be a lot better.

Maybe my senseless ramblings will help trigger a thought by a real mechanic on here. If not... please ignore my craziness.

 

[jesserose17]

Doe it have the hesitation when sitting while you have your head under the hood? I still have an idea floating in the back of my head on a reason... I'm not a mechanic, but I have to ask. Do you have underdrive pullies?

No, it idles great & smooth, doesn't hesitate when I take off. No underdrive pullies - pretty much stock.

 

[jesserose17]

My crazy mind makes me keep thinking about:

When my front rotors were warped we rebuilt my rearend and replaced the broken ABS sensors. Which activated my ABS system again. My car honestly ran crappy when we fixed the ABS. I replaced the rotors and my car ran better. Strange huh? Watching the charge guage... before and after the rotor change was interesting. I think my rotors were warped enough my ABS was trying to engage, and dropped my voltage in the car causing it to run bad.

I feel like my car isn't getting the charge it should and is really noticable at idle or just above. When I get past that 2,000 rpm range the charge guage goes up and things seem to be a lot better.

Maybe my senseless ramblings will help trigger a thought by a real mechanic on here. If not... please ignore my craziness.

That's certainly strange about ABS affecting your engine performance... Are you sure there's no short with ABS wiring?

 

[gcomfx.com]

That's certainly strange about ABS affecting your engine performance... Are you sure there's no short with ABS wiring?

Putting new rotors on didn't fix any shorts in the wiring did it? All kidding aside... they work fine.

 

[mystang94gt]

I'd put my bet on the EGR as well. Your EGR does NOTHING at WOT so its not surprising that it runs great when you floor it. But at part throttle it isnt opening like it should be and that can cause the bucking your talking about.

However on second thought when mine went out I got a code from the code scanner it was bad.... Hmmmm.....

 

[gcomfx.com]

Just thought of a reason my car might be stuttering... it's been a while since it's had it's fix! Crazy junky stang.

 

[jesserose17]

Guys, thanks for your inputs... I'll keep you posted on what I find when I get a chance to work on it.

 

[jesserose17]

I carefully cleaned the MAF with ethyl alcohol & Q-tips - no difference. I checked the EGR - the diagram moves freely with vacuum pump. Very little carbon build-up. Replaced the EGR Valve postion sensor - still no difference.

Should I replace the TPS? I am getting frustrated and getting ready to push it off the cliff!

Additional info - cold, no missing. During warm-up & operating temp, it misses/bucks more between 1200-1800 rpm in 2nd & 3rd gear AODE with light acceleration. Doesn't miss while cruising.

 

[95strokerPSU]

Sounds like what my car started to do today. I don't have a working tach in my car right now but I would guess it's about that same RPM range that it started backfiring like crazy, and anything over 2k seems to be fine. Tomorrow I'll be going back over to the shop and if I find anything out I'll post it. Good luck

 

[jesserose17]

However on second thought when mine went out I got a code from the code scanner it was bad.... Hmmmm.....

My "Check Engine light" isn't on at all... so should I check with code scanner? I am trying to determine if it's worth $$ to buy the code scanner.

 

[gcomfx.com]

Does it surge when slowing down and coming to a stop like at a traffic light? That's what mine still does.... after the EGR delete. Before that it was almost impossible to drive and wouldn't idle for crap (sometimes) which probably meant it was sticking.

I'm trying to determine if this last surging problem is vacuum related or what. Keep us posted, as it seems there a few of us with symptoms in this area.

Strange that it's mainly the AODE guys. What mods do you have?

 

[BlueOvalStangGT]

My car drives fine cold and warm but when its warm and you try to slow down for a traffic light or something the car will stall. Now it stalls at like every light. I took the EGR off my old intake and it still does it and I've cleaned the MAF, IAT and the sensor thing in the TB. Could my problem be tied in with yours? Im gonna delete the EGR next and see if that makes a difference.

 

[gcomfx.com]

On mine I could see the EGR not moving when you revved the car. I put a screw driver in one of the slots and the EGR plunger popped back then the car cleared up on idle.

It was pretty obvious for me.... hopefully you'll have good luck too. I still have a mild surging but not NEAR as bad as it used to be. Before I literally had to drive with my foot on the gas and brake. It was the only way to get it to idle while stopping.