shudder at specific RPM

[baucke]

First of all, I've lurked here for a while and made quite a few repairs using the search function. Most notably sending the ECM off for repair and replacing the idle air valve. So thanks to everyone for that.

And now for something I can't seem to find a clear answer on:

First - no codes.

I have an 02 QX4 that if you are cruising and lift off the gas slightly (but still giving it some throttle) it shudders like it has a fouled plug. Seems to be RPM related at about 2000-2200. Can replicate the same issue at lower speeds while accelerating slowly as the revs hit the same point. Keeping the RPM steady, the shaking continues until the RPM moves out of the range.

It idles fine, and good power anywhere other than that specific range. Turning off OD does make it go away as well, which makes me think it is definitely RPM, and not speed related.

Could this be an odd problem with a coil?

[EdBwoy]

Does the shudder happen at the same spot if you give it gas while in park? And what RPM is the vehicle idling at when warmed up?

[baucke]

First - quick correction - shudder is at 1500. Not sure why I typed 2000 before.

Yes, it seems to have the same shudder when it's in park. It's tough to hold the RPM steady while giving it some gas, but I do get a similar shudder as the RPM slowly pass through 1500. Idle speed is 800-850 with no load, in park with A/C off. Drops to 675 when put in gear and sitting still.

Sorry it took so long to replay. Battery died, and I thought I had an alternator problem. Just a dead battery, but wanted to drive the truck for a few days to make sure that was all OK before trying to tackle anything else.

[baucke]

I've poked at the plugs and wires, nothing changes the shudder.

Some more fourm digging looks like there are some transmission issues that cause a similar behavior. Possibly replacing the fluid would help? Can any one weigh in on that? Thanks.

[Rockwood]

The torque converter comes out of lockup when you back off the gas, and never goes into lockup when you turn off OD.

New fluid will often fix converter shudder. Valvoline High Mileage ATF has a pretty good reputation, is synthetic, and is pretty affordable. It does have a strong odor, so try not to spill it.

You get a little less than 4 quarts when you remove the transmission drain plug, so a gallon does a good job at refilling. 3 of those drains and fills gets you roughly 70% new fluid. Drive at least 10 to 20 miles between drains and fills.

I think you are on the right track.

[baucke]

Thanks. I get the same behavior at low speed/low throttle. Is it safe to conclude the torque converter is not locked up in that condition as well?

I’ll change the fluid regardless. It’s cheap(ish).

[baucke]

Success!
Got the fluid changed yesterday, and so far so good. Everything is smooth.

Thanks for the help.

[towncarblue]

im having the same issue. when i first start the pathfinder in the morning , it runs perfectly.
after the pathfinder warms up a bit i get the shudder. tried replacing the transmission fluid but i still have the same issue.

[baucke]

wish i could help you. Although I seem to have solved the low speed problem with transmission problem, I now have a new issue. After driving it for a while now, my high speed shudder is back, and is now coupled with a no start when warm.

Anyone want to buy a QX4 with $200K? (kidding, maybe)

[EdBwoy]

I have seen the warm-start issues from a bad crankshaft/camshaft sensor. At minimum I'd check the sensors for,dirt and grit as well as whatever surface they're picking up signal from, and keep advancing,up the troubleshooting ladder [replacement] as your pocket allows.

Then, I also had an almost similar problem after redoing an engine and the vehicle needed the idle air relearn procedure performed.
What was odd about this one was that cold starts were always fine. If I drove the car around and shut it off, the following warm-start would fail. Car just revved once at startup then died. If however, I blipped the throttle a little as it turned over, it would keep running with no issues.
And idle air relearn as well as the 2 other throttle body learning procedures fixed that.

[Rockwood]

If you have a high speed vibration now that seems to reoccur at the same MPH, I would look at u joints. You have enough miles where they may be a problem.

[baucke]

I have seen the warm-start issues from a bad crankshaft/camshaft sensor. At minimum I'd check the sensors for,dirt and grit as well as whatever surface they're picking up signal from, and keep advancing,up the troubleshooting ladder [replacement] as your pocket allows.

Then, I also had an almost similar problem after redoing an engine and the vehicle needed the idle air relearn procedure performed.
What was odd about this one was that cold starts were always fine. If I drove the car around and shut it off, the following warm-start would fail. Car just revved once at startup then died. If however, I blipped the throttle a little as it turned over, it would keep running with no issues.
And idle air relearn as well as the 2 other throttle body learning procedures fixed that.

Thanks. I started another thread to chase down P0011 (in the same general function area as the sensors), so far so good on that. Since I added some seafoam, the code cleared and I have not had a warm start issue. Every time I park, I wait a minute and try to restart the engine.

If you have a high speed vibration now that seems to reoccur at the same MPH, I would look at u joints. You have enough miles where they may be a problem.

Honestly, this was my initial thought, or perhaps something else in that chain of components. However, when it occurs, I can turn off the overdrive and the vibration stops when the RPM increase which points to engine or transmission. Thinking its more than likely transmission since I can't replicate the vibration by slowing down with the overdrive off to match the RPM to where the shudder occurred, and I did not get the shudder. Based on other threads here, I put some lubeguard in, which seems to have helped. Time will tell.

Thanks everyone for all the help. If I can keep this truck running for a couple more years, that's all I need.

[anthonyerco]

Shudderfix from NAPA. Have a GX470 that had horrible shudder @ 200,000 miles. Did a drain and fill, nothing. Did another drain and fill and added shudderfix and within 20 miles it was completely gone. Good reviews on product as well.