Very high idle when in park/driving

My 93 Ford Tempo 4 cyl. has a problem. Now that it’s cold, if I drive for a distance of 20 miles or so it is starting to rev up really high when I put it into park! It also will be revving while I’m driving it, which is a bit unnerving! I can get it to go about 40 without touching the gas at all. I’m sure it has to do with the temperature, as if it’s warm the car doesn’t do this at all.

I don’t want to take it in without any idea what could be wrong…they will just start putting in parts and I don’t want to spend much $$ on this as we plan on buying a new(er) car after Christmas. Can you give me an idea of what may be wrong so DH and I can attempt to fix it on the cheap?

The signal from the engine cts (coolant temperature sensor) could be indicating to the engine computer that tha engine is MUCH colder than it actually is. The engine computer, in response to this “cold” signal, will send a lot of fuel to the engine. A poor, high resistance connection to the cts, could cause the signal to be wrong to the engine computer. Wriggle, or disconnect and reconnect, the wire connection (“plug”) on the cts. You could do voltage and resistance test to the cts; or, just change it. Choice.

you could have a bad ISM idle speed motor it is a small motor that makes the idle go up and down.

The simplest explaination would be a large vacuum leak. Check under the hood for any loose or damaged hoses or any other noticable leak points.

All the suggestions are possibilities. Greasy Jack’s suggestion, of vacuum leak(s), is one that a non-mechanic can check out. The rubber vacuum hoses on the engine are subject to break down and splitting, from engine heat, over the years. Look at the hoses on the engine. If (particularly) the end of a hose attaching to the engine is cracked, or split, that end needs to be cut off, or, replace the hose.
With the engine idling, listen for hiss of air somewhere on the engine. The hiss may lead you to where the vacuum leak is. Show your mechanic that area.
Some parts that the rubber vacuum hoses go to could be leaking vacuum. The power brake booster diaphragm can rupture. YOU can check this by running the engine at idle, in PARK. Press the brake pedal. If the engine speed goes up, that could be a bad power brake booster. The fix is the replacement of the power brake booster.

I’m thinking it may be the CTS as suggested! After reading the response DH thought it might be the CTS because we also have a problem with it during the summer; it shows that the temp is getting high when it isn’t. It just goes up on the gauge for a few seconds, then returns to normal. I hadn’t thought about that problem when I posted the first time (had no idea that it could be related!) Where is the CTS located on this engine so we can wiggle the connection? It’s probably not the brake booster, as this vehicle runs normally during short trips in cold weather (even when I do lots of short trips on one day), or even long trips in warmer weather. It’s only when it is very cold and it runs for more than 15-20 minutes at those cold temps. I’ll listen for hissing, but I’m not sure I can hear it over the death rattle of the ticking engine! LOL

If it’s not a vaucuum leak, as already mentioned, I would suspect the throtle position sensor (TPS).