Gomedic

Hello All! Wonderful info here! I am the "new" owner of my son's mustang. V6 auto with 218,000 miles on body and 55k on replacement motor.
Some issues I was dealing with:

Rough idle and loss of power. I cleaned the IAC and MAFS as well as the TB. Car runs better, but still has poor mileage and odd shift points around 35-40 mph. Sometimes at 75 mph if feels like it stutters a little. Car starts fine and idles around 700rpms then goes up to 1100 and back down.
When I get on it, it runs well but feels like it shifts rather hard. One of the threads pointed to possible Throttle Position Sensor.

Mileage is around 15-17 mpg on highway at 73-75 mph. Is that normal?

I'm a very novice mechanic but I have more money than my son. LOL. So it is now my project. I appreciate ALL help!

BabyGT

To ease your mind a bit the 35-40 mph shift point is kinda weird. At 35 steady speed it wants to stay in a gear just below what I would think it should be in. It won't shift up until 40, then you can let back off to around 36-37 and it will stay in the higher gear and run less rpms. I really hate this particular shift point choice cause it makes a world of difference in the loudness of my exhaust from the two gears at 35, not to mention I'm sure I'm using up a bit more fuel.

Fuel mileage doesn't seem to far off depending on driving habits.

Does the rpm pulse up and down or is just that once at start up and is fine after?

RyansQuick6

I assume there's no codes?

I'd go ahead and run some seafoam through it, do a search, there's a lot of how-to articles on it, then do a regular tune up. Go ahead and replace plugs and wires, and it may need a new coil. For plugs, just get regular NGK TR-5's, DO NOT USE PLATINUMS, for wires, I'd recommend MSD, or Motorcraft, and if it needs a coil, then ONLY buy a Motorcraft or you will hate youself.

These cars can last a pretty long time if properly maintained. One member has I believe over 400,000 miles on his with no major repairs.

BabyGT

There was a guy over 600,000 with no major repairs, and he traded it I'm for a couple grand then saw the same car sell at an auction for like a couple hundred lol

Gomedic

Only code is for O2 sensor. RPMs pulse at idle. I replaced the TPS anyways, seeing how it was fairly cheap and easy.

I am reading about the Seafoam treatment now. Sounds like good results.

RyansQuick6

O2 sensor codes are typically caused by another sensor further upstream. It's rare that the O2's fail as opposed to the other sensors that will show that code. What is the actual code you're getting?

petrock

An O2 code will effect your gas milage and can cause drivability problems depending on which O2 sensor is throwing the code and which code it is. 15-17mpg sounds low to me, but I could be wrong since most of my wifey’s driving in her ’98 mustang V6 is all over the mph range. If memory serves from the last fill up, its somewhere in the high 20’s to low 30’s on her ride.

As for the shift points, when was the transmission fluid & filter changed last? If you don’t know then now might be a good time. Burnt up, dirty and/or low tranny fluid can cause strange problems like this.

Gomedic

Ok Autozone just told me the code was for bank 1 O2 sensor and then told me there was a problem with the communication between my car and the scanner. Gave me a number of "a guy" that does electrical analysis for $60 and I should have that done. Not sure is this is his brother in law or something...

Put some Seafoam in the tank yesterday. I will do the whole Seafoam cleaning this week. Have not noticed any difference with the TPS replaced. Still has odd idle issues and kind of stutters at around 35 mph.

Noticed the belt tensioner appears to be broken! So I am replacing that this week too...
My son told me his mechanic friend "noticed it" when he replaced the alternator...sounds like a hack job to me...

I just ordered a CAI from American Muscle today.

RyansQuick6

How did he replace an alternator with a broken tensioner??? lol

BTW, what brand CAI did you order? If it's not AFE, go ahead and order an AFE recharge kit, and clean out the new one and charge it with the AFE oil. Otherwise, you'll be posting again in 2 months about why are your O2's on again. Other brand's thin oil will coat the MAF and cause a CEL for O2 sensors.

Gomedic

It's a SR cai. Thnx for the info on the recharge kit. Will do that tomorrow.

The tensioner has what looks like a hairline fracture goin through it. So I'm going to replace it.