troy1

I have a 1995 3.1L (3100) when cold the engine hesitates under light throttle if you get into it you can clear is out. As is starts to warm up it goes away usually only happens once during warm up. If you let it sit and cool back down sometimes it does will do it again. Gave it plugs, wires, tps , fuel filter, t-stat. There are no codes present , and uses no antifreeze, but the temp gauge does fluctuate some. Goes up when you slow down and drops when you speed up only has a 7 - 10 degree change when I watched it on the scanner.

Manny_boy

when you changed your thermostat, did you bleed the air from your coolant system? An air bubble stuck in your coolant system, could cause the temp gauge fluctuation you describe.

...for the hesitation, that almost sounds like a vacuum leak due to old intake manifold gaskets. When the car warms up, the gaskets expand and seal better, but when cold, they contract, and if there is a crack, or one area of the gasket is no longer sealing properly, it could cause a vacuum leak. Does your idle speed also fluctuate when the car is cold?

A good test for the intake manifold is this: Take a can of intake or carb cleaner, with the engine running spary it around the intake. If your car stumbles, wherever you sprayed that caused the stumble, you have a vacuum leak caused by a cracked intake gasket.

troy1

Yep I think I got all the air out. Idle does flucuate some but it when you first start up the car and put it in gear it will bounce around 500 rpm or so at idle does not always do it and it does not matter hot or cold.

enginetune

With a scanner. Look at block learn and integrater. 128 is optimum for both. If one or both are way off, it indicates the computer is working harder to compensate for something( vacume leak). If, when cold, you hit the throttle quick, does it seem to backfire a little in the intake? If so it's too lean when cold. In the old days it was a choke problem. Now it's a coolant sensor problem. One thing I just started using to fix this, and other things as well, provided all the basics are up to standard, is a fuel system cleaner. Motorvac to be specific, not a cheap one. Removing deposits from the fuel rail and injectors results in a night and day differance in cold starts and operation.