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Overheating and rpm going crazy don't know why?

While in park the temperature gauge moves above normal ,it also doesn’t stay at idle speed it drops below. Fans don’t come on by themselves they do if I turn on ac. While driving temperature goes up also more than normal while ac is off. when I accelerate to 3000 rpm it feels like it lags a little then it goes after hard jolt all the time. Today couple of times after doing that it reved back up to 3000 rpm by itself like stuck but car still went at speed I was in originally and my foot is off the gas pedal while thiz happened. So far all the changes to minivan are tune up , mass air flow sensor, coolant sensor on radiator and motor, oxygen sensor1 bank 1, throttle body ,Thermostat, speed sensor. We have done smoke test to check for leaks mechanic said there were none so we really need help we are stumped don’t know what it could be .

Year make and model would help us a lot along with how well this mystery vehicle has been maintained.???
Correction, it’s an uplander but we need the year and other info.

So far all the changes to minivan are tune up , mass air flow sensor, coolant sensor on radiator and motor, oxygen sensor1 bank 1, throttle body ,Thermostat, speed sensor.

What Motor??? the entire engine!!!

Engine temp sensor there may be two. One to control the gauge reading and another to feed the PCM it’s data.
I’d guess it may be the one that feeds data to the PCM.

But I also think you may have something interfering with the throttle cable, or the fly by wire control of the throttle if so equiped.


Because of the hard shifts? I think it could also be that the transmission cooler isn’t cooling enough because the fans aren’t coming on, so the tranny is overheating.

2006 chevy uplander 3.5
It was the coolant sensor from motor or transmission that we changed not the motor itself.
We are worried it might be transmission because today as I was driving same hard jolts but again after I got to 40 mph the rpm hit the 3 it went down and it went back up as if stuck with loud rev noise but the mph was the same the car does not go faster while doing this.

I’m sorry, but that is a nearly impossible sentence to parse. Can you clarify?

Everytime while driving if I make a stop and take off there is a hard jolt while accelerating. I was driving in blvd and reached 40 mph I feel the car is lagging a little and the Rpm gauge is reaching the number 3 at this time then all by itself it seems as if Rpm needle goes down and revs itself but the car itself doesn’t accelerate at those times I wait a couple of seconds I slow down then keep driving.

Could it be transmission solenoid?

That’s one problem you should take care of first. Engine cooling fans should come on be themselves. Could be as simple as a sensor, since the fans seem to work when the a/c comes on

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If you notice the engine is overheating but the engine fans don’t come on when idling or say when waiting in the drive-thru line at the local McDonalds, that needs to be addressed as your first priority. I’ve had to fix that problem on my Corolla a couple of times, so it isn’t an uncommon problem. There’s a temperature sensing gadget used to decide when the fan should come on. That part screws into the engine & the end of it lives in the coolant, and that gadget can corrode and fail. Next, there’s a relay used to turn the fan on, and that part can fail too. And then there’s the fan itself, the motor on that can fail. Your local shop should be able to figure out which of those problems it is, as long as the “fan doesn’t turn on” problem occurs while they have it at the shop.

If the engine is overheating even though the fan is turning on, that’s a different problem, and won’t be as easy to diagnose. I don’t think that’s the problem here, right?

The jerking/jolting sounds like you are getting hard shifts from your transmission. There’s some possibility the engine overheating is contributing, so best to fix the overheating problem first. If the jolting shifts continues, let us know. You may just need to have a routine transmission service done.

Any time the engine is severely overheating, you need to stop the car & turn it off asap. Some engine cooling can be effected by turning on the passenger compartment heater to full hot and the blower to max.

Tomorrow I’m taking to mechanic and see what’s wrong I’ll update when I can.