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Discussion Starter · #1 ·
The car is a 1995 Mustang with a 3.8L engine, manual transmission, and the car drives like a bat out of hell, but there seems to be a dead spot in the first 1/4 of the throttle where the RPMs will drop big time (as if it just lost power) and then right after that dead spot is where it's highly responsive. I replaced the MAF sensor, the TPS, complete tune-up, cleaned the coil pack because it wasn't reading for a cylinder (reads great now), new plugs and wires, checked the EGR (it's fine), checked for vacuum leaks, and a lot of other things that aren't related to the ignition ... I'm doing all this for free to help a friend with her car, and this is the last piece of the mechanical puzzle (still got plenty I'm doing to the interior and exterior), but I'm officially stumped now. I seriously appreciate any help I can get with this.
 

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Do you know if this car has an aftermarket tune on it by chance? The v6 Mustangs in 1994-95 had full functioning OBDII(not the 5.0 though) so you might want to scan it for any possible codes to help narrow down the basic cause.
The TPS is usually a common cause for dead spots especially at idle or just above but since you replaced that it's scratched off the list of possibilities. Misfires due to intermittent/no spark or dirty fuel injectors can cause what you describe too. Other problems that typically cause acceleration stumble include lean issues like from vacuum leaks(check over the PCV hoses), low fuel pressure(bad FPR, weak fuel pump, or clogged filter), weak/no spark caused by low coil voltage or bad coil(s), and even retarded ignition timing though this last one is probably the least likely.
Since you said that there was a coil issue already I would suspect that.
 

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Discussion Starter · #4 ·
Do you know if this car has an aftermarket tune on it by chance? The v6 Mustangs in 1994-95 had full functioning OBDII(not the 5.0 though) so you might want to scan it for any possible codes to help narrow down the basic cause.
The TPS is usually a common cause for dead spots especially at idle or just above but since you replaced that it's scratched off the list of possibilities. Misfires due to intermittent/no spark or dirty fuel injectors can cause what you describe too. Other problems that typically cause acceleration stumble include lean issues like from vacuum leaks(check over the PCV hoses), low fuel pressure(bad FPR, weak fuel pump, or clogged filter), weak/no spark caused by low coil voltage or bad coil(s), and even retarded ignition timing though this last one is probably the least likely.
Since you said that there was a coil issue already I would suspect that.
The car is bone stock, but I haven't tested the fuel pressure yet, and I just got the ignition timing tool in yesterday so I'll be checking that, too. I read in the Haynes manual that there's not a way to adjust the timing on this car anyway (without a special scan tool), but I'm still going to check that. Also haven't done the fuel filter but that's on the list of things to do. There weren't any vacuum leaks, though the EGR diaphragm was stuck until I got it unstuck and it works now.

Thanks for the help, I'll (hopefully) be checking this all out today. I'll keep y'all updated.

Just in case you want to test the throttle position sensor.

https://easyautodiagnostics.com/ford/3.8L/mustang-tps-tests-1#1
Thanks for this, I'll be testing this on that sensor even though it's new (I've told many people just because a part's new doesn't mean it's good out of the box ... I've had to replace an alternator three times within two days just because the new ones were faulty).
 

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I don't know if you noticed. But there are more tutorials at the end of the last page of the TPS troubleshooting. Its a decent site to bookmark if you might need it later for some older make and model vehicles. Not spectacular, but handy. Just hit the homepage button and save it.
 

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Discussion Starter · #6 ·
I don't know if you noticed. But there are more tutorials at the end of the last page of the TPS troubleshooting. Its a decent site to bookmark if you might need it later for some older make and model vehicles. Not spectacular, but handy. Just hit the homepage button and save it.
It was the TPS, even though it was a new part there was still a dead spot in it that I wouldn't have known about without the help of that tutorial. Thanks to you guys she's running like a bat out of hell, took her for a test drive and "accidentally" got her up to 95 on a highway. Seems like she's forgiven me for being a Chevy guy now. Thanks again for the help!
 
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