[JCook236]

I have a '93 Mustang LX, 2.3L, 166600 Miles

Can drive around at 35-45 mph all day long with no problems but if I put some pedal in it and go 55-60+ mph the RPM's slowly decline, speed reduces, then RPM's drop to zero and car will stall. I then coast to the side of the road, turn the key off, turn it back on and the car starts fine and will run 35-45 mph again just fine.

The "Check Engine" light has never come on. Had the codes read anyway and they showed nothing.

I've Changed:
Fuel Filter, Fuel Pump, Spark Plugs, PCV Valve, Mass Air Flow Sensor and Air Filter.

I've Checked:
Vaccum lines, Fuel Lines and Fuel Pressure - All Good.

Notes:
Noticed the timing jumps around a little bit now and then.
Fuel mileage doesn't appear to be what it used to be.

Could it be a MAP sensor, Throttle Position Sensor, or one of the other sensors?

Any ideas? Thank you for your time!

JCook

[89GTVert]

Does it seem strictly speed related? or could it be throttle position related?

[Mr coupe]

Restricted exhuast? If you tap on your converter does rattle or anything? If you really want to ~ unbolt your egr valve or o2 sensor ( I know it will be loud and annoying) and take it for a drive to see what happens. If you can cruize past 55 then you might have a clogged up cat converter

Let us know what you find out

[JCook236]

Will try it and report back. Thank you for the input.

JCook236

[JCook236]

Tapping on the converter didn't produce any noise (rattle).
Haven't tried disconnect of o2 sensor yet (few things came up) but did find out the following:

Car revs ok in park and neutral and I was able to redline it.

I then tried rev'ing the engine to different RPMs and holding it for a few seconds before letting off with the following results:
Held RPMs at 3000 = Everything ok
Held RPMs at 3500 = Everything ok
Held RPMs at 4000 = Amost died but recovered
Held RPMs at 4500 = Engine died and took 2 attempts to restart.

When I tried the 4500 RPM test, after a few seconds the RPMs starting dropping slightly and I kept having to push the gas pedal down a little more to keep it at 4500, after a few more seconds the engine died.

Then today I drove the car to autozone to pick up some dielectric grease so I could swap in a spare EDIS unit I have and on the way there here is what I found.

- Found that if I let off the gas (foot off pedal) when I see the RPMs starting to go down, coast a few seconds, then get back in the gas, the RPMs would go back up a little and the car didn't stall. Was able to go 60-65 mph using this method.

- After a few miles of this I noticed the RPMs weren't going down so I floored it and got up to 80 mph. Drove for 4-5 miles at 80 mph with no problem. Pulled off the road and came to a complete stop, then gunned it to get back on the road and got up to 80 mph with no problem. Drove it around a little while longer and no stalling and no RPM drop, although it did seem to lack as much power as it usually has.

Not sure what to do now. Didn't fix anything so I know it's broke.

[sgtb]

I had a similar problem with a '93 2.3 when I went for a test drive after doing some stuff under the hood. It turned out to be a stupid mechanic error, in this case me... I left the air duct off between the air filter and the throtle body. Once I put that on it's was fine.

Maybe there is something wrong with the new mass airflow sensor or something related to it.