...while its warm. I had this issue last fall, but during winter it didn't cause any problems so I didn't know what to look for. Since its warmed back up its started happening again. The best way to describe it is that it feels like my truck is sneezing. It has no loss of power. I can't get it to do it in the driveway, whether in park or w/ gas and brake pressed.

To complicate matters (??) I was driving about 70mph, smelled a bit of smoke, and the Service Engine Soon light came on ...and flashed several times before staying on solid. That freaked me out so I took it to the shop. It had thrown the Random Misfire code (P0300??). They replaced the cam & crank shaft position sensors. I've had no more of that issue.

For a week or so, the RPMs didn't jump, or not as often, or not noticeably, ...or something. I also wasn't driving it at the normal warm/hot part of the day so I didn't have a good test. I thought I was out of the water but upon driving it at the normal times it started happening again.

I can't get it to act up regularly w/ the mechanic. I had him in the car once when it was acting up and he told me that it was my overdrive going out. He shifted it into 3rd and told me "Watch, it won't do it now." It proceeded to do it for him. I left it with him and since he was unable to reproduce it he didn't want to just go swapping out parts.

He asked when the last tune up was and I'm ashamed to say that I can't recall. Its been more than 4 years and I'm ashamed to go back any further than that. I realize that complicates troubleshooting it. (I've got a tune-up tentatively scheduled for this afternoon.)

Its got 274k miles, 2 oil leaks (rear main seal, and one from the front of the engine). I get 18-ish mpg (used to get 21-ish). I've changed the oil pretty religiously at 3500-4500 miles.

Any ideas as to what's causing it? I appreciate any tips.

 

Sounds to me like the torque converter is going in and out of lockup, is your CEL on at all, is there any codes? We also need some more info on the vehicle, what year is it, is it 4X4 etc

 

Check engine light's not on (since the crank/cam shaft position sensors were replaced) and its throwing no codes.

Its a '97 LT 4x4.

Re: torque converter, is that going to mean I need a new transmission as well? What can I do to check it, or how can I determine its the torque converter?

Had a tune up over the weekend (fuel filter, plugs & wires, rotor, dist cap) so we'll see what happens.

 

Hopefully a tuneup will help, the transmission should not be bad if the torque converter is going in and out of lockup, it could be the TCC/PWM valve in the valve body of the transmission, if it is that tho and is not setting a code yet it will eventually, most likely the P1870 excessive torque converter slippage, or it can be something as simple as the throttle position sensor (TPS), you can test the TPS with a multi meter, it should be a smooth transition from 0.5 at idle to 4.5 volts at WOT . A local transmission shop should be able to monitor the slippage of the transmission with there scanner.