2002 TB RPMs Surging at highway speeds

[nolongerseemssofar]

I have a 2002 TB LS w/ 133k that I've just bought. At highway speeds (50-70mph) the RPMS are sitting at around 1500 to 1600 on level road. If i start to speed up slowly, the RPMs will surge back and forth between 1500 and 2000 RPMs. If I give it a little more boot to beyond 2000 RPMs it will stop surging and speed up normally. I'm new to this engine so I'm not sure if this is a big problem or not. I can say that I will be replacing the fan clutch soon as it sounds like a jet engine from time to time, but I don't really think there's a link there. Any help will be greatly appreciated!

 

[Mounce]

For the surging, is it shifting gears back and forth or staying in one gear? And for the fan clutch, it will sound like that sometimes like at start-up or time to time during idle or at slow speeds when it's audible over the engine and road noise. Are you getting a code for the fan clutch or anything else? I believe when the fan clutch becomes a problem in the PCM's eyes it'll throw the Reduced Engine Power light along with a Service Engine Soon code about it. Someone with more experience than I will chime in after daybreak.

Welcome to the Nation!! ​

 

[nolongerseemssofar]

It's staying in fourth while surging.

There is no code yet for the fan clutch, just trying to baby this thing take care of anything that comes up asap.

 

[Mounce]

Gotcha, well give the guys a few hours to wake up and they'll make their rounds and talk to you about the issues.

 

[Harpo]

I think it's the normal in and out of lockup you are experiencing.

 

[BlazingTrails]

Mine was just doing that too, I added a cooler, and a bottle of Lucas transmission treatment and it is driving much better. The shifts are firmer as well

 

[nolongerseemssofar]

Thanks! Since I just got it and I'm not sure what the maintenance history is, I'll probably have the transmission flushed and go from there. Thanks for the help!

 

[gmcman]

What's the condition of trans fluid/level? Take it out again and leave it in 3rd gear and if the RPM's fluctuate again then we can go from there. The trans will lockup in 3rd but naturally at a higher RPM.

Lockup occurs with light pedal pressure and will unlock on coast.

 

[Wooluf1952]

Welcome

In case you haven't heard:
http://gmtnation.com/forums/topic/218-welcome-to-gmtnationcom-heres-the-story/

Without a maintenance history, a throttle-body cleaning would also be a good idea. And you are close enough to the very important 50k mile transfer-case fluid change.

 

[KNBlazer]

I say it's your tranny, take it to a shop that does free diagnostics....

 

[nolongerseemssofar]

What's the condition of trans fluid/level? Take it out again and leave it in 3rd gear and if the RPM's fluctuate again then we can go from there. The trans will lockup in 3rd but naturally at a higher RPM.

Lockup occurs with light pedal pressure and will unlock on coast.

Thanks for the info! I'll take it out in the morning in 3rd and see what happens.

 

[Cable810]

I have the same issue but its only when I go up hill. Its not constantly doing it just occasionally does it. It doesn't do it while driving on a level road or wheeling. My RPMS on a level road are in the 1,800 range and that's driving 55-60mph.
I've read that an IAT sensor that's getting bad can cause surging while driving. There is an article that a good read on it but I can't paste it... look up "Bad Iat sensor symptoms aa1car" The article is by aa1car.com

 

[Sparky]

I KNOW I KNOW!!

Well OK, I can't say 100% for sure but it sounds like what I had going on with my old vehicle.

TCC lockup valve may be worn. Mine was, and it wouldn't stay in lockup. Yes, it was in 4th gear the whole time but lockup would slip in-out-in-out causing RPM surges. It got worse, stopped staying locked at all. Then it started slamming gear shifts as the temp was getting high and it thought it was slipping.

4L60E relatively common problem (moreso on the older ones). Not a "hard" fix if you don't mind putzing around in the valve body a bit and swapping a few pieces. If you can follow directions it isn't too bad. Just takes some time. This fixed my issues completely on my old 4L60E, so when I got my Trailblazer I installed the same kit when I serviced the trans just to be safe (and it had some signs of wear inside that could have led to the same issue). 200k miles on my Trailblazer and zero issues still

http://www.ebay.ca/itm/4L60E-4L65E-1996-2006-1870-P1870-CODE-BUSTER-COMBO-KIT-Corvette-Servo-Kit-Book-/270874884435?pt=Motors_Car_Truck_Parts_Accessories&hash=item3f1166b953&vxp=mtr

 

[The_Roadie]

Good morning and welcome! If you just bought it, and it's over 100K, and you don't have a full maintenance history with receipts, then ALL fluids need changing ASAP. Especially the transfer case, whose change interval is a surprisingly short 50K. Plugs are another urgent item. Use only Delco 41-103. There's plenty of threads discussing the required 100K maintenance, and when I say all fluids, it's ALL. Brake fluid flush as well as power steering, tranny, both diffs, transfer case, and coolant.

 

[dmanns67]

I had a very similar issue on my 07 TB while cruising in 4th and the RPMs would surge while traveling at 55-60 mph without applying any pressure to the pedal. Root cause ended up being a dirty/oily MAF sensor.

I know your 02 does not have a MAF, but for those that do have the IAT, is it possible to clean the IAT with MAF sensor cleaner? Might be a good place to start from my personal experience.

 

[nolongerseemssofar]

Thanks everyone for all the info! Looks like this guy is going to have to save up some cash.

 

[nolongerseemssofar]

is this kit the same as the ebay one?

https://www.rockauto.com/catalog/x,carcode,1398719,parttype,8532

 

[Sparky]

No. The ebay one is a combo setup that the seller has put together. Transgo SK4L60E, Sonnax pinless accumulators, Transgo hardened separator plate, etc.

That ATP kit looks like mainly just a set of springs, which the Transgo kit does have, but not the rest of the stuff. The primary thing that you need if your issue is what mine was is the TCC valve, and that ATP kit does not have it, nor does it have new separator plate seals (at minimum, I recommend replacing the separator plate entirely with the new one in the kit).

 

[nolongerseemssofar]

Ok thanks, sparky!