Ford Repair: my mustang drives itself, mustang v6, costly repair

Question
QUESTION: I have a 98 mustang V6 3.8 manual. When I am in 1st, 2nd or 3rd gear it is ok. But when I step on the clutch (in gear or not)to change from 3rd to 4th the RPM's will go from 2000 to 3400 instantly!!! and will not drop till I release the clutch. When this is happening I do not need to give the car any gas at all and it will hold it's speed at 45 and up mph until I bring the car speed to below 40 mph. It is like it has cruise control. BUT MY CAR DOESN'T. Can you please tell me what is wrong. I am a single mom of 2 and use this car for work. (pizza delivery) The last thing I need is to have a costly repair or someone fixing things that are not the real problem. Oh, and most of the time when I shut the engine off for a few minutes, then drive it again. . . magically the problem is gone. . .?? But it comes back - my children say it's haunted.

ANSWER: Is the check engine light on? Either way, run it down to your local parts store, have them read the codes. I will need the codes themselves, not the definitions that the parts guys will give you. Don't buy anything they try to sell you until you tell me what the codes are.

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QUESTION: Sorry it took a while. Maybe you didn't know, but they told me everywhere I went that in the state of California they no longer offer a free diagnose or code reading. Auto Zone said it's rules changed regarding that about 4 months ago because someone tried to sue them for a lot of money. So a code reading at the repair shop will cost me $60-$80. Or I can buy my own reader for $60. So, would it be alright if I get back to you on the codes. Funds are a bit low. The last time I took it to a place to change the oil, he noted my paper work and said some of the codes that came up were P1120 & P1151. Does that help or is that just more problems I need to add to the list???

Answer
You have one of two problems, causing your symptoms. A faulty TPS, which I am leaning towards, or a faulty MAF. The TPS is relatively cheap, and both parts are relatively easy to replace. If you buy the vehicle repair manual, and are half way mechanically inclined, you could tackle this. Just take your time unplugging the wire harness connections.