Slight surge @ 1500 rpm

So, I've got this bit of a surge at 15-1600 rpm and around 40mph. It only seems to occur when the overdrive shifts down. There is very little throttle at this rpm and just wonder what some thoughts may be? I've got new coils, plugs (copper) cleaned TB new TPS. Engine runs well otherwise with good gas mileage (20ish highway), though does idle a bit rough overall. I just can't seem to nail this one down.

What you are describing just sounds like the trans downshifting. Can you clarify? ie. The trans down shift and THEN there is a surge?

Yes, it's is after the shift. It is sort of like a throttle "hunt". If I hold the throttle steady right at the above mentioned speed/rpm there is a slight surge in the rpm's up and down. Doesn't seem to do it any other time. Very odd.

Try it with O/D switched off and see if the engine surges at the same speed/rpm. It sounds like you may be describing the trans trying to hunt for the right gear, going a bit too slow for overdrive. In any of the automatic vehicles I've had in the past, I always switched off O/D while city or lower speed driving for this very reason, it's an annoyance. I generally didn't put it in O/D till I hit the 45 mph range.

CactusJacked said:

Try it with O/D switched off and see if the engine surges at the same speed/rpm. It sounds like you may be describing the trans trying to hunt for the right gear, going a bit too slow for overdrive. In any of the automatic vehicles I've had in the past, I always switched off O/D while city or lower speed driving for this very reason, it's an annoyance. I generally didn't put it in O/D till I hit the 45 mph range.

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I do drive with the OD off usually, as it seems like that is the case. Just the hunt seems more apparent with this particular vehicle.

Was the replacement a Mopar TPS?

I was having an issue with my KJ just not accelerating properly
There would be such a bad lag from when I press the pedal to when it would speed up and it would make the RPMs jump up
May have been partially due to sitting higher now and catching more wind
My fix was a TPS from O'Reilly's (NAPA didn't have any in stock)
I got the best one they had and it's a world of difference
Very responsive now, I can actually FEEL the pedal being stiffer and going from any speed I can accelerate very easily
But, since you replaced the TPS (maybe faulty or not good quality?) and the other stuff I wouldn't know what else to try

Hope you find the fix !

Any torque converter shudder?

If not...I'd put $20 down to say that it's coming. Mine does the same thing. TC is shot. Just running mine to the ground...

If you want to try to get this corrected I would suggest dealer trans service first.

dude1116 said:

Any torque converter shudder?

If not...I'd put $20 down to say that it's coming. Mine does the same thing. TC is shot. Just running mine to the ground...

If you want to try to get this corrected I would suggest dealer trans service first.

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Describe your symptoms? Curious, as I had that thought. Seems to shift solidly overall though with no slippage.

On the TPS, aftermarket. Purchased at Autozone. Don't remember the brand, but I think it was their "house" brand.

Just to eliminate tune issues- Clean port & the IAC -Throttle body well.
Use a scan gauge into the OBD2 port and advance the throttle to around the 1500-1600rpm and see if when you hold throttle at that rpm, if the rpms are surging.
Mine was surging bad when held exactly at 1700 rpm in park.
I ended up replacing the IAC and TPS (used Mopar TPS) and all is well.

LibertyTC said:

Just to eliminate tune issues- Clean port & the IAC -Throttle body well.
Use a scan gauge into the OBD2 port and advance the throttle to around the 1500-1600rpm and see if when you hold throttle at that rpm, if the rpms are surging.
Mine was surging bad when held exactly at 1700 rpm in park.
I ended up replacing the IAC and TPS (used Mopar TPS) and all is well.

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I actually had done that. And mine is 1500-1600. That's when I changed the TPS to no significant change, but a little better. When I cleaned the AIC/TB it was just nasty, in fact my TB took almost two cans of cleaner to clean. Not sure if it had ever been done. I was considering getting a new AIC as well, but I wanted to toss out the problem before I blindly keep tossing money at sensors. I cleaned my MAS as well, maybe just change all three to mopar parts (not sure if the ones in are stock) and just be done with it.

I really don't think it is a trans issue. The truck pulls hard off the line and shifting is smooth, but who knows?

Check to make sure the throttle plate is clean around the inner edge.
Open it a bit and get the carbon off the edges of the plate all the way around.
One other thing to note is when mine was surging, it was also misfiring only at that rpm too.
Was a low count, not enough to set a dash engine light.
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New coil packs were necessary.
The snap on scanner can also read transmission codes.
Good to know if there are any pending etc.

Geof3 said:

Describe your symptoms? Curious, as I had that thought. Seems to shift solidly overall though with no slippage.

On the TPS, aftermarket. Purchased at Autozone. Don't remember the brand, but I think it was their "house" brand.

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Driving along, accelerating as normal. About to go into TC lockup and I get a slight surge in RPM's then they drop to normal. Maybe 2-300 RPMs or so. Sometimes I'll get a shudder like going over a rumble strip but it doesn't happen all the time. Probably only 10% of TC lockups.

I'd get a video for you but the Jeep is down for maintenance right now. If you post a video of your tach while driving I'll tell you if it's the same thing as what I see.

dude1116 said:

Driving along, accelerating as normal. About to go into TC lockup and I get a slight surge in RPM's then they drop to normal. Maybe 2-300 RPMs or so. Sometimes I'll get a shudder like going over a rumble strip but it doesn't happen all the time. Probably only 10% of TC lockups.

I'd get a video for you but the Jeep is down for maintenance right now. If you post a video of your tach while driving I'll tell you if it's the same thing as what I see.

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I don't have anything like that happening. It is only at this one spot, doesn't do it at any other point, nor do I experience any shuddering, at least not t this point. Going to try a the MOPAR parts change. That's the hard part about figuring stuff like this out. Usually a process of elimination.